Closing in on large building boiler design...

[Maine Way]

Hello All,


I’m designing a heating system for a large Victorian, and flexibility is important.


Parameters:


The plan is to move in this fall, and heat first and second floor, about 2800 SF total. The walls are mostly uninsulated (15%) but the attic has fiberglass batts and some blown-in cellulous – maybe R-24. Most windows are vinyl replacement.


We will endure one winter or two before re-siding and blowing insulation from outside.

There are plans to expand to fully finished basement and partial attic, all to be heated eventually with the same system. These add another 1800SF and 6 more windows.

Hot water demand will include 5 showers, although three would likely be the max in use at the same time plus 2 kitchens and 2 laundries.

Radiation for the system will be mixed, with cast iron baseboard, radiant floors (mixed types) and one panel radiator. These would service a number of small zones, as some rooms would be occupied occasionally. We would be looking for various temperatures for the supply, aiming to achieve condensation in the return.

Proposed System:

I was thinking of using two combi NG boilers (considering AB-155C AquaBalance Combination Wall Mount Gas Boiler, 125,000 BTU) with a 30 Gallon Stainless Steel Hydronic Buffer Tank and perhaps with a Two Stage Boiler & Setpoint Controller designed. The distribution is designed with primary and secondary piping.

The qualities I think will work with this system:

1. Two boilers will allow for the swings in demand over the years as insulation gets added and expansion of floor space happens and when house and rent out unit are more occupied or less. They also offer redundancy, which is important for rental unit and for Maine, where severe weather can cause many-days of delay in service (sudden spike in demand).

2. Likewise with the hot water demand, each unit can provide 4gmp, so one boiler would meet the demand most of the time, but the second could fire to deliver more if needed.

3. Buffer tank would allow for micro zones at different temperatures and should be able to achieve condensation and without short cycling while also providing hydraulic separation for secondary piping with it’s own circulators.

4. I am not very knowledgeable about the controller, but I understand it will help make efficient use of two boilers.

Questions:

1.I don't mind spending money on a good system, as long as it is the right one. Do the features of this system make sense for what I am looking for?
2.Is there a good reason to consider a more expensive boiler? The specs of the Weil-McLain seem to meet my needs.
3.Is the controller a good idea? Will this allow me to utilize the turn-down ratio of both boilers to the best advantage? Does it also control the DHW, or that would need some separate master control to fire the second boiler if demand is high?
4.Any comments are welcomed.

 

[John Gayewski]

Have you added up the total cost? This sounds expensive for a rental. I would think there could be a much cheaper design with similar comfort.

I saw you have a decent amount of info, but have you added up the total radiation?

How many units is this rental? How many zones. How will the bills be split?

 

[Sponsor]

 

[Maine Way]

Thank you for the reply John.

Cost:

I am looking at about 10k in equipment ($2015 x 2 boilers, $1142 for the buffer tank and $500 to $1000 for the controller plus about $4000 for circulators, primary piping, and accesories) . I have bought the radiation used. I am doing the work myself, so there is where the savings happen. I was quoted 60k for a new heating system which would have used one boiler 199kBTU combi Navien. They price in running all new pipe in an old house, which can be tricky. I've already got the pex run to upstairs and basement access makes downstairs easy. So, yes, it is expensive, but saving on labor makes affordable.

I have installed one 13 zone system before (start to finish), but just a conventional cast iron gas boiler.

Radiation:

5 rooms at 16' cast iron baseboard = 31,200 BTU (at 160 deg water) or (40,800 BTU at 180 deg)
Radiant floor downstairs = 42,000 BTU
Radiant floor upstairs = 15,750 BTU
Radiant floor Basement = 45,500 BTU
Panel Radiator = 4,500 to 6,000 (160 or 180)
Attic Panel Radiators = 13,500 to 18000 BTU (160 or 180)

So, on days needing 180 Degree water (maybe before insulating walls or very cold days I achieve 170k BTU of radiation. I do think the boilers are oversized for this load, since it won't draw this all at the same time. Ideally, it can use lower temps for longer cycles and run more efficiently. But, I do need to consider 3 showers going on a cold day and dishwashers running too - off the same boilers. Also, having redundancy is important, and one boiler could likely keep up with 85% to 90% of winter days alone. Lastly, there is a small price difference between the 100k and 125k models.

How many zones:

4 zones of cast iron baseboard.
4 zones of radiant floor (2 basement, 1 first floor, 1 second floor)
2 zones of panel radiators

Most of the house will be my home
Basement is a separate rental with separate entrance

In other properties I manage I have found including heat and pricing it in is best for this area.

I manage some higher end inventory that includes hot water and is a furnished rental. That model works well because price point screens out abusers of free hot water (or pays for it).

Shawn

 

[John Gayewski]

OK I'm assuming you've done the heat loss Calc and you can actually heat the areas, you plan to use radiant floors, with radiant floors (this being a limited by the low temp and surface area of the floor).

One thing I'm seeing here, you don't need to size the water heating in with the heat load. Your water has priority and normally isn't designed to do both at the same time. When you need water the boiler will heat the water and then go back to heating the house they don't run in parallel. This saves on size of boiler and keeps run times longer, not to mention if your house cools down through a shower you have a problem.

Just make sure the boiler can do your domestic load.

It seems like you may have a good plan. Just a warning mixing radiation types can be a very large headache. The dynamics of different types of radiation and the way they cycle can make effeciancy hard to manage. A lot of people go to lengths to keep one type of radiation.

Otherwise keeps us posted.

 

[Fitter30]

Controller taco sr506 with sr506 exp 12 zones with dhw priority.
Any condensing boiler with return water over 130* 86% efficient. Boiler gets its 95% efficiency from the condensate.
Any new pumps taco makes a e series that use a ecm motor that is high efficiency.
Radiant floor systems use lower temp 80* than cast iron radiators.

 

[Dana]

Even prior to insulation as long as there is glass in the windows, doors that shut, and no gaping holes the 99% design heat load of a 2800' Victorian with vinyl replacement windows is <100,000 BTU/hr @ 0F, and it could even by < 75K. After improvements it's likely to come in under 50,000 BTU/hr even after adding in 1000' of code-min insulated finished basement and 800' of code-min finished attic. Having the ability to deliver 170KBTU/hr is pointless, and pretty expensive to buy and install, even on the used radiation market. If you have a heating history on the place with the existing boiler it's possible to ball-park the design load fairly accurately using fuel use between meter readings against heating degree-day data. Details on how to run that math live here.

The whole house load-adder of an insulated finished basement would near zero or even less than zero due to the lower stack effect infiltration drive from air-sealing and insulating the basement. Installing 45KBTU/hr of radiation in an insulated basement is INSANE, and would cost more than insulating the basement walls to the current code min (=R15 continuous insulation walls) with oh-so-expensive 2.5-3" of closed cell spray polyurethane foam. (There are cheaper ways to get there without creating mold farms, but the details of your foundation and foundation sill etc. matter.) A 1000 square foot basement insulated to code min walls and R8 EPS under either a new (radiant) slab or a subfloor over the slab will usually come in well under 10,000 BTU/hr, often under 5000 BTU/hr.

Similarly, the load-adder of an air sealed insulated attic space could be negligible or negative due to improved blocking of the top of the stack-effect stack. Insulated to current code minimums 800' of finished attic space would likely come in under 10,000 BTU/hr @ 0F unless you're adding a lot of window or skylight surface area, and could be substantially less.

As a rule of thumb, the emittance of the radiation at condensing temps is roughly 1/3 it's 180F either average water temp (AWT ) or entering water temp (EWT) rated output. Installing enough radiation to cover the loads at the wintertime average temp is reasonable, but anything beyond that is a bit silly, unless the goal is to eventually run the system with air source hydronic heat pumps (that need to run <100F water to maintain excellent efficiency & capacity.)

Getting to the optimal system doesn't happen randomly or by hackery. It's not rocket science but you have to do some math. Start by running room-by-room load numbers of the house in the "before improvements" condition of the house using a Manual-J type load calculator. Even freebie/cheapie online tools such as LoadCalc or CoolCalc can deliver reasonable results as long as you are sufficiently aggressive on the inputs (i.e.: assume the house is pretty air tight, not super leaky, and assume the maximum R-values that could be reasonable for any pre-existing insulation. If you also have a fuel-use whole-house load number, compare the load tool's whole house number to your fuel use number. The fuel use is a measurement, using the existing boiler as the measuring instrument, and using wintertime only fuel use will usually be more accurate than a Manual-J. Follow up with an "after improvements" room by room load calculation.

The radiation needs to be fairly proportional to the room loads to have any hope of running mostly in condensing mode with reasonable room to room temperature differences, even if micro-zoning, otherwise you'd need to set the outdoor reset and buffer tank temp for the room/radiation with the highest temperature needs, which is bad for average efficiency. If the radiation is sized to cover the design load with ~155-160F water in the "before improvements" version of the house, in most cases it would then be able to cover the "after improvements" load with <140F water on design day, and run in condensing mode nearly all of the time, except perhaps during Polar Vortex disturbance cold snaps when it is 10s of degrees cooler than the 99% outside design temp.

If you scale the radiation appropriately you won't necessarily need or want to micro-zone the place, and may not need buffer tanks. Zoning floor by floor is usually more than adequate for both comfort & efficiency as long as the room by room radiation is proportional to the loads. If the attic doesn't require much radiation to heat that zone and even it's design load is less than the minimum firing rate of the boiler it's fine to size the radiation to be able to deliver the min-fire output of the boiler at 140F, and let it short-cycle on that zone a little bit during the shoulder seasons rather than ludicrously oversizing the radiation for the load, which could lead to temperature overshoots under some conditions.

While it's tempting to DIY the whole shebang to save money, it's also important to properly value your time. If you start with a better sculped calculated approach with a more simplified system it won't cost $60K- it could be half that (or even less) if you can lose the micro-zoning and the buffer tanks. Doing the whole thing with just one right-sized (for the whole house heating load) boiler and one or two indirect water heaters (sized to fill the biggest bathtub) may come in cheaper than a pair of oversized combis, and would have a wider modulation range on the low end. (Do you even have a big enough gas meter to handle a pair oversized combis?)

 

[Maine Way]

Thank you fitter30.

That looks like a good product. A few questions about controllers, since I know very little.

1.The hot water will be on demand from the boiler. Will the boiler already set this as a priority when hot water is drawn? On the same topic, if one boiler (I have 2 in the setup) is supplying adequate flow to satisfy hot water demand, will the second boiler remain dedicated to heating? This may be important when it's -20F outsider and a couple people take long showers.
2.Do controllers help to send the correct temperature water to each zone (cast iron at one temp and radiant floor at another), using a mixing valve and the buffer tank? or do I need a different accessory for this?
3.Do controllers mix down return water to achieve condensing temperature? With microtones this may be a problem.

Shawn

 

[Maine Way]

Amazing reply here Dana!

I think I may have over designed this!

The house was a foreclosure and no data is available on fuel use. The house had massive cast iron radiators in every room (before it went through a winter and everything cracked), which were part of a steam set-up at one point then converted hydronic by oil, then the oil burner was replaced by NG Carlton 123K BTU burner. The house has a lot of large windows. First floor has 9' Ceilings and second has 8'5 ceilings. No gaping holes.

Walls are true 2x4, mostly void ballon frame with plaster and lath and board sheathing with clap boards.

The basement has 11' ceilings and half of it is full walk-out with large windows. The basement walls are 12" thick brick above grade and granite blocks below. We would like to maintain the brick finish inside and out for about 50% of the walk-out wall (so about 25% of basement wall area), and insulate selectively either inside or outside for the other 50% of the walk-out wall. The wall which is mostly against grade will be mechanical and spray foamed. Since we are pouring a new slab, we are looking at 4" foam topped with concrete. We thought we would run pex in the concrete for radiant and stain or color the concrete as a floor finish.

The attic space is all glass on the gable end. There are two large skylights. We plan on rigid foam and a vent space in a 6" cavity available between rafters. But, considered furring out for a little more insulation there.

I will look closer at room-by-room calcs and determine what changes need to be made in the radiation. Some rooms requirements will change greatly with improvements and some less, since a couple rooms are half insulated. So, I may base radiation on final design.

Part of the idea for micro zoning is due to a guestroom not being used often. One bedroom is for an elderly person, who prefers the heat on 85. And beyond this, the 10-year plan for the building is to be further divided into 2 apartments. So, controls from each apartment would be needed.

I definitely see you point about the false economy of DIY. The 60K was for a single combi, and the engineer sized it at 200k BTUs. It was a simpler system with no buffer tank, but did have 5 zones. Most of the money was in labor. I do enjoy this type of work and am able to dedicate most of my time to the house project. I've done all the plumbing and electrical and spent about 15k (four bathrooms and a fair number of added electrical). The combined quotes for electric and plumbing came to 40k. Obviously I'm not billing my time, but I bought quite a few new tools with that money.

Perhaps I should go back to the original system design and do the one boiler with no buffer tank and not worry about redundancy or the added efficiency of using a smaller boiler in the shoulder season and ramping up to two boilers in the winter. I am just going down a rabbit hole here?

Again, THANK YOU! This is really helpful and I and I am reassessing my direction now.

Shawn

 

[Fitter30]

Thank you fitter30.

That looks like a good product. A few questions about controllers, since I know very little.

1.The hot water will be on demand from the boiler. Will the boiler already set this as a priority when hot water is drawn? On the same topic, if one boiler (I have 2 in the setup) is supplying adequate flow to satisfy hot water demand, will the second boiler remain dedicated to heating? This may be important when it's -20F outsider and a couple people take long showers.
2.Do controllers help to send the correct temperature water to each zone (cast iron at one temp and radiant floor at another), using a mixing valve and the buffer tank? or do I need a different accessory for this?
3.Do controllers mix down return water to achieve condensing temperature? With microtones this may be a problem.

Shawn

Thank you fitter30.

That looks like a good product. A few questions about controllers, since I know very little.

1.The hot water will be on demand from the boiler. Will the boiler already set this as a priority when hot water is drawn? On the same topic, if one boiler (I have 2 in the setup) is supplying adequate flow to satisfy hot water demand, will the second boiler remain dedicated to heating? This may be important when it's -20F outsider and a couple people take long showers.
2.Do controllers help to send the correct temperature water to each zone (cast iron at one temp and radiant floor at another), using a mixing valve and the buffer tank? or do I need a different accessory for this?
3.Do controllers mix down return water to achieve condensing temperature? With microtones this may be a problem.

Shawn

1 Call for dhw turns heat off dhw on. Boiler /water heater controls water temps except with outdoor reset
2 no it doesn't separate the water temp has to be done with piping valves and pump
3 no return water temp is the product of design. System are normally design for 20* temp difference. 160* from boiler 140* return.

 

[Dana]

Amazing reply here Dana!

I think I may have over designed this!

D'ya think? (It's easy to go hog wild for no good reason...)

... then the oil burner was replaced by NG Carlton 123K BTU burner...

...which at ~80% efficiency delivers at best 100K to the house, not counting distribution losses. If it was able to heat the house reasonably, the design load is clearly <100K.

The house has a lot of large windows. First floor has 9' Ceilings and second has 8'5 ceilings. No gaping holes.

If the replacement windows are low-E (check with a lighter or candle flame- if one of the 4 reflections has a different color it's low E), assuming an outside design temp of 0F, at 0F outside, 70F inside the windows are losing 20-25 BTU/hr per square foot. If they are older clear glass double panes call it 35 BTU/hr per square foot.

Walls are true 2x4, mostly void ballon frame with plaster and lath and board sheathing with clap boards.

With no top plates (common in balloon framing) those stud bays are essentially flues sucking air 24/365. With the bays empty with typical 1x plank sheathing & 7"-10" exposure clapboards you're looking at about 15-18 BTU/hr per square foot of wall area @ 70F indoors, 0F outdoors. Stuff those stud bays full of cellulose and that drops to ~5-7 BTU/hr per square foot under design conditions. Before insulating the walls be sure check and correct any window flashing deficiencies. Empty stud bays dry really quickly, so even if some wind-driven rain gets into the rough window opening it's no disaster. If the stud bay is full of cellulose or fiberglass the wood stays wet, putting the sheathing & framing near the rain-leaky window at risk of rot. (I suspect most insulation contractors in Maine are aware of these issues, but according to Murphy's Law if you don't check you'll end up with the contractor who is clueless.)

The basement has 11' ceilings and half of it is full walk-out with large windows. The basement walls are 12" thick brick above grade and granite blocks below. We would like to maintain the brick finish inside and out for about 50% of the walk-out wall (so about 25% of basement wall area), and insulate selectively either inside or outside for the other 50% of the walk-out wall.

An 8" thick double-wythe brick wall (no cavity) is ultra-lossy and air leaky to boot, good for about R1.5-R2, and the above grade wall would be losing about 35 BTU/hr per square foot at design condition. This is an energy disaster above grade, and still of concern below grade, losing 20 BTU/hr per square foot at the frost depth line, more above that. Even 2" of sheet EPS and a thin-brick veneer (interior or exterior) would cut that to 7-8 BTU/hr per square foot above at a 70F temperature difference, making it somewhat comparable to a cellulose-filled balloon framed 2x4 wall.

The wall which is mostly against grade will be mechanical and spray foamed. Since we are pouring a new slab, we are looking at 4" foam topped with concrete. We thought we would run pex in the concrete for radiant and stain or color the concrete as a floor finish.

It's good to "float" the slab edge with 1.5-2" of EPS between foundation walls and slab edge to pressure relieve the slab's expansion, keeping the foundation walls from moving. If you go straight up the interior side with 2" EPS it would mitigate the extreme lossiness of the brick or granite walls, as outlined above.

The attic space is all glass on the gable end. There are two large skylights. We plan on rigid foam and a vent space in a 6" cavity available between rafters. But, considered furring out for a little more insulation there.

Cut'n'cobbled rigid foam is impossible to make reliably air tight, but as long as there is soffit-to-ridge venting in each stud bay that will work. A more reliable approach (except under skip sheathed slate or cedar shingle roofs) would be to install 2" of HFO blown closed cell foam (not the HFC stuff which is cheaper but lower R and more climate UN-friendly) directly on the underside of the roof deck. With HFO blown foam that would run R14-ish, about $2.50 per square foot. Then filling the remaining 4" with cellulose deliver another R14-R15. That's only R28-R30 still well below code min (=R49), but it's very moisture safe in all of IECC zone 6 (= most of Maine), whereas an air-leaky cut'n'cobbled foam board into an unvented cavity below the roof deck can become a moisture trap putting the roof deck at risk. The performance of the unvented full cavity fill is also higher than a cut'n'cobble job, and more assured over the long term.

Perhaps I should go back to the original system design and do the one boiler with no buffer tank and not worry about redundancy or the added efficiency of using a smaller boiler in the shoulder season and ramping up to two boilers in the winter. I am just going down a rabbit hole here?

Again, THANK YOU! This is really helpful and I and I am reassessing my direction now.

Shawn

Run the load numbers see where it comes in. Only from that vantage point can the safe & economically-sane options become more clear. Even if you love this kind of work, it becomes a pretty serious hobby and time sink when microzoning an entire house.

 

[Maine Way]

I am not sure of the quote format will show up in my reply. I've typed my replies between your responses.


...which at ~80% efficiency delivers at best 100K to the house, not counting distribution losses. If it was able to heat the house reasonably, the design load is clearly <100K.

That's true, but we are adding finishing the basement and part of the attic and have added two bump-outs to the kitchen with 6 massive windows (effectively nearly doubling square footage) and have added considerable hot water demand. So, the new system would need to work for that - on the other had we are upgrading some of the envelope, which will reduce heating requirments.

If the replacement windows are low-E (check with a lighter or candle flame- if one of the 4 reflections has a different color it's low E), assuming an outside design temp of 0F, at 0F outside, 70F inside the windows are losing 20-25 BTU/hr per square foot. If they are older clear glass double panes call it 35 BTU/hr per square foot.

Replacement windows are low-E. Downstairs windows were all replaced except the kitchen. We added 6 low-e windows there. There is one left that is an old wooden sash but has a storm.

Upstairs windows were only replaced in one bedroom (4 windows). We are replacing most of the rest - (7 more of them) with low-E. and have left the stained glass alone (several large windows) and a couple double hungs in the back, which are wooded sashes.

With no top plates (common in balloon framing) those stud bays are essentially flues sucking air 24/365. With the bays empty with typical 1x plank sheathing & 7"-10" exposure clapboards you're looking at about 15-18 BTU/hr per square foot of wall area @ 70F indoors, 0F outdoors. Stuff those stud bays full of cellulose and that drops to ~5-7 BTU/hr per square foot under design conditions. Before insulating the walls be sure check and correct any window flashing deficiencies. Empty stud bays dry really quickly, so even if some wind-driven rain gets into the rough window opening it's no disaster. If the stud bay is full of cellulose or fiberglass the wood stays wet, putting the sheathing & framing near the rain-leaky window at risk of rot. (I suspect most insulation contractors in Maine are aware of these issues, but according to Murphy's Law if you don't check you'll end up with the contractor who is clueless.)

There is a top plate at the attic. There is no plate at the second floor level. There is probably a lot of chimney effect there. We plan to blow them when we refinish the outside. It's been great for running wire in exterior walls.

An 8" thick double-wythe brick wall (no cavity) is ultra-lossy and air leaky to boot, good for about R1.5-R2, and the above grade wall would be losing about 35 BTU/hr per square foot at design condition. This is an energy disaster above grade, and still of concern below grade, losing 20 BTU/hr per square foot at the frost depth line, more above that. Even 2" of sheet EPS and a thin-brick veneer (interior or exterior) would cut that to 7-8 BTU/hr per square foot above at a 70F temperature difference, making it somewhat comparable to a cellulose-filled balloon framed 2x4 wall.

Yeah. This is bad. It's stunning brickwork with arches over the basement windows and in good shape. We are struggling to figure which parts to cover up. The side garden or the pool room and karaoke lounge in the basement (uplighted exposed brickwork as a featured finish). We have decided to cover parts of it from the inside for minor spaces. But the main space is too cool. The outside area under the deck we will insulate outside. So, we are left with some of the wall we may leave untreated inside and out.

It's good to "float" the slab edge with 1.5-2" of EPS between foundation walls and slab edge to pressure relieve the slab's expansion, keeping the foundation walls from moving. If you go straight up the interior side with 2" EPS it would mitigate the extreme lossiness of the brick or granite walls, as outlined above.

That's a good detail. We will float it for the thermal break with the wall as well as manage expansion.

Cut'n'cobbled rigid foam is impossible to make reliably air tight, but as long as there is soffit-to-ridge venting in each stud bay that will work. A more reliable approach (except under skip sheathed slate or cedar shingle roofs) would be to install 2" of HFO blown closed cell foam (not the HFC stuff which is cheaper but lower R and more climate UN-friendly) directly on the underside of the roof deck. With HFO blown foam that would run R14-ish, about $2.50 per square foot. Then filling the remaining 4" with cellulose deliver another R14-R15. That's only R28-R30 still well below code min (=R49), but it's very moisture safe in all of IECC zone 6 (= most of Maine), whereas an air-leaky cut'n'cobbled foam board into an unvented cavity below the roof deck can become a moisture trap putting the roof deck at risk. The performance of the unvented full cavity fill is also higher than a cut'n'cobble job, and more assured over the long term.

I don't feel comfortable without a fully vented roof. Sun baked asphalt fails quickly without venting. And ice dams also become a problem. So, every bay has a through vent space. Below that I am open to how to insulate. Maybe run vents and spray foam under them for a seal below the vent and high r-value per inch. Any maintenance issue become a headache though...

Run the load numbers see where it comes in. Only from that vantage point can the safe & economically-sane options become more clear. Even if you love this kind of work, it becomes a pretty serious hobby and time sink when microzoning an entire house.[/QUOTE]

I am working on running numbers and will get back. Some of the radiation is a bit set at this point. Half the downstairs has radiant installed under cement board and is ready for tile. I would not think of doing a staple-up under the hardwood in the living rooms - not a great conductor and would need another zone and temp anyway since wood and tile take different temps. 30% of the upstairs has radiant run already. And the rest will be cast iron baseboard. I don't think we would consider ripping open ceilings for a staple-up under the hardwood on the second floor. Also, the upstairs is two wings with separate stairs. So, due to separation of spaces, and more than one emitter type, we are already committed to a certain number of zones. I can see combining two of the bedrooms, although one is not used often. Basement and attic will need to be separate as well. We may be stuck with a number of zones.

Thank you again Dana for the considered reply. It is encouraging for me in tackling the heating and hot water system for the building.

Shawn

 

[Maine Way]

I've run heat calcs room-by-room (or by zone in some cases) for upstairs and down. I created a spreadsheet, which was modified from one I found. I calculated heat loss based on outside walls (wall and windows separate) and ceiling and floor areas. I ignored interior partitions, assuming mostly heated space on the other side. I was a little unsure about air infiltration. But, with new replacement windows and sealed walls and ceilings I am thinking it may not be a lot.

Below posted image of an example of a room calc.

The total house calcs came to 55k BTU needed for a 70 degree difference. My area of central Maine has lower design temp than zero, as far as I could tell it's -7 degrees. We do see -20 on the thermometer a few times in January. So, the assumption of zero outside may not be ideal.

I ran the calcs with the upgrades. And it came to 40k BTU. This mostly considered adding insulation to walls that don't have it, and replacing the couple old windows left.

Neither of these calculations include the planned, finished basement or attic (which together newly double the area of the house). Furthermore, hot water is not included (house will have 5 showers, 2 dishwashers, and 3 laundries).

If the calculations are accurate, even with some extra capacity, a 100k BTU boiler might keep up with demand once improvements are made and also to include basement and attic.

 

[John Gayewski]

Do the heat loss for the basement and attic. The numbers might surprise you.

Also if you figure a 70 degree difference, on those days where it's neg. 20 you'll only heat to 50. Use the design day for your area. You'd at least get to 57 on those cold days. I usually figure for heating to 72 on design day. That way when I'm below design day a got a couple extra, which in this case gets you to 59. More than survive able, plus I don't think you can rent a space that isn't sized properly.

Air infiltration does add something even with nice windows. It's not a lot per space but it does add up. The heat loss /load is the main reference point for heating a structure. You need to be precise in my opinion.

 

[Dana]

I've run heat calcs room-by-room (or by zone in some cases) for upstairs and down. I created a spreadsheet, which was modified from one I found. I calculated heat loss based on outside walls (wall and windows separate) and ceiling and floor areas. I ignored interior partitions, assuming mostly heated space on the other side. I was a little unsure about air infiltration. But, with new replacement windows and sealed walls and ceilings I am thinking it may not be a lot.

The in it's current condition with balloon framing and air leaky brick walls in the basement the air leakage heat loads are probably substantial. Assume it's at least something like ASHRAE 62.2 ventilation rate levels, which would be 0.3 cfm per square foot of conditioned space floor area, plus 7.5 cfm x (1+ # of bedrooms). It could be higher than that, but could also be lower.

After air sealing and insulating it'll be closer to the Building Science Corporation's 0.1 cfm per square foot + 7.5 cfm x (1+ # of bedrooms). If you luck out and make the place significantly tighter than that (unlikely) plan on adding mechanical ventilation.

Below posted image of an example of a room calc.

The total house calcs came to 55k BTU needed for a 70 degree difference. My area of central Maine has lower design temp than zero, as far as I could tell it's -7 degrees. We do see -20 on the thermometer a few times in January. So, the assumption of zero outside may not be ideal.

I ran the calcs with the upgrades. And it came to 40k BTU. This mostly considered adding insulation to walls that don't have it, and replacing the couple old windows left.

The R-value of an empty 2x4 wall is roughly R4, and with wood siding and full dimension- your heat load page (was that from a load tool?) showed R3, which is substantially more lossy than reality. Seriously, use LoadCalc or CoolCalc (both of which will overshoot reality even with aggressive input values) for those numbers. Central Maine's 99% outside design temps are still in only single digits below zero. Dropping the outside design temp to -7F only adds ~10% to the load numbers. Don't put a thumb on the scale by using a cooler than 99th percentile temperature bin. If one uses ASHRAE's recommended 1.4x equipment oversize factor for the 99% load and the outside design temp is actually 0F it won't start to lose ground until ~ 30F. Since temps don't stay in the -20s for very long (a few pre-dawn hours on the coldest night of a Polar Vortex disturbance week), with a less leaky and insulated house the thermal mass of the house and it's contents limit the rate at which it loses ground too.

A 190' bedroom would need a minimum of 190' x 0.1cfm + (2x 7.5cfm) = 34 cfm to maintain reasonable to excellent indoor air quality overnight, if not the full ASHRAE 62.2's 190 x 0.3 cfm +(2x 7.5 cfm)= 72cfm. At a 70F indoor to outdoor difference that would be 70F x 0.018 x 34cfm x 60 minutes/hr = 2570 BTU/hr, which is a good argument for heat recovery ventilation. With an HRV the ventilation load drops to about 500 BTU/hr, which is roughly the heat output of a pair of non-copulating (sleeping) adult humans in bed. At ASHRAE 62.2 rates the ventilation load is roughly twice that, but that is arguably too high for health in a Maine winter due to how dry the wintertime outdoor air is. (Ideally you'd hold the line at an indoor RH of 30% @ 70F, not lower.)

Neither of these calculations include the planned, finished basement or attic (which together newly double the area of the house). Furthermore, hot water is not included (house will have 5 showers, 2 dishwashers, and 3 laundries).

If the calculations are accurate, even with some extra capacity, a 100k BTU boiler might keep up with demand once improvements are made and also to include basement and attic.

The additional load of the basement + attic is low, assuming you're air sealing and insulating to some reasonable level. The attic is above fully conditioned space- no floor losses, the basement is between ~45-50F dirt (with insulation under the new slab, no less) and fully conditioned space above, and usually has less window area than fully above grade floors. Run those load numbers using a real load tool.

A 100K combi boiler isn't enough for reasonable hot water service, barely keeping up with just one full flow shower in the dead of winter. But a 100K boiler + indirect is overkill for this house. Assuming a heat load (all-in, basement + attic included) of 50K in the "after upgrades" version of th house, a boiler wiht 1.4x 50K= 70K would be more than enough for both heat and hot water. Properly set up, an 80K condensing boiler would heat a 50 gallon indirect in less than half the time of a standard 50 gallon gas water heater, a short enough time that the house won't lose even 1F in indoor temperature when giving priority to the indirect on the coldest hour of the year.

 

[Maine Way]

Do the heat loss for the basement and attic. The numbers might surprise you.

Also if you figure a 70 degree difference, on those days where it's neg. 20 you'll only heat to 50. Use the design day for your area. You'd at least get to 57 on those cold days. I usually figure for heating to 72 on design day. That way when I'm below design day a got a couple extra, which in this case gets you to 59. More than survive able, plus I don't think you can rent a space that isn't sized properly.

Air infiltration does add something even with nice windows. It's not a lot per space but it does add up. The heat loss /load is the main reference point for heating a structure. You need to be precise in my opinion.

Hello John,

I've looked at adjusting the delta T as suggested. Outside temp -7 and inside at 72 (delta of 79).

I also did cals based on that for attic and basement.

I had the following results.

Upstairs and downstairs combined 60.2 (previously 55K at delta of 70 deg)

Upstairs and downstairs combined (after upgrades) 42.6 (previously 40K at delta of 70 deg)

As expected, upgraded envelope was less affected by change in delta T.

Basement and Attic assume upgraded design and delta T of 79:

Basement 19.6K (11' ceilings and walk-out - above grade -for half of the wall. About 315SF is uninsulated brick to keep exposed brick look inside and out for that portion of wall - which accounts for half heat loss.)

Attic 5.6K

Air infiltration component in my equations still needs refining and I am working on that part..

Thanks for the feedback!

 

[Maine Way]

The in it's current condition with balloon framing and air leaky brick walls in the basement the air leakage heat loads are probably substantial. Assume it's at least something like ASHRAE 62.2 ventilation rate levels, which would be 0.3 cfm per square foot of conditioned space floor area, plus 7.5 cfm x (1+ # of bedrooms). It could be higher than that, but could also be lower.

After air sealing and insulating it'll be closer to the Building Science Corporation's 0.1 cfm per square foot + 7.5 cfm x (1+ # of bedrooms). If you luck out and make the place significantly tighter than that (unlikely) plan on adding mechanical ventilation.

I think I will shoot for a little leaky rather than add ventilation. When we blow the walls we will get a blower test for the building and see what's leaking.

The R-value of an empty 2x4 wall is roughly R4, and with wood siding and full dimension- your heat load page (was that from a load tool?) showed R3, which is substantially more lossy than reality. Seriously, use LoadCalc or CoolCalc (both of which will overshoot reality even with aggressive input values) for those numbers. Central Maine's 99% outside design temps are still in only single digits below zero. Dropping the outside design temp to -7F only adds ~10% to the load numbers. Don't put a thumb on the scale by using a cooler than 99th percentile temperature bin. If one uses ASHRAE's recommended 1.4x equipment oversize factor for the 99% load and the outside design temp is actually 0F it won't start to lose ground until ~ 30F. Since temps don't stay in the -20s for very long (a few pre-dawn hours on the coldest night of a Polar Vortex disturbance week), with a less leaky and insulated house the thermal mass of the house and it's contents limit the rate at which it loses ground too.

A 190' bedroom would need a minimum of 190' x 0.1cfm + (2x 7.5cfm) = 34 cfm to maintain reasonable to excellent indoor air quality overnight, if not the full ASHRAE 62.2's 190 x 0.3 cfm +(2x 7.5 cfm)= 72cfm. At a 70F indoor to outdoor difference that would be 70F x 0.018 x 34cfm x 60 minutes/hr = 2570 BTU/hr, which is a good argument for heat recovery ventilation. With an HRV the ventilation load drops to about 500 BTU/hr, which is roughly the heat output of a pair of non-copulating (sleeping) adult humans in bed. At ASHRAE 62.2 rates the ventilation load is roughly twice that, but that is arguably too high for health in a Maine winter due to how dry the wintertime outdoor air is. (Ideally you'd hold the line at an indoor RH of 30% @ 70F, not lower.)

I figured the wall at an R1 per inch of wood. With 7/8" boards and 3/8" lath and stack clapboards (about 7/8") I get about R2. The paster itself may add something, but not much. The air space may be leaky in many areas, thus not doing much. But, it may be not too leaky in areas. Anyway, I figured R1 for that to be safe. Certainly going from R3 to R4 for that element impacts numbers in a surprising way! I fiddled with my spreadsheet and was surprised!

Understood. I will continue to look at a delta of 70 degrees to size the system. Often a cold snap early January can have multiple consecutive night lows in -20s and -10s by day. We had a week that never climbed above zero two winters ago.

The current plan for the bedroom is for one, non-copulating adult - had to laugh - (my mother-in-law). She is from the tropics and likes the heat on 80. As you point out, the problem in winter is inadequate humidity. Many people run humidifiers inside in the winter, especially if prone to nose bleeds. I don't use them and probably don't achieve 30%RH.

The additional load of the basement + attic is low, assuming you're air sealing and insulating to some reasonable level. The attic is above fully conditioned space- no floor losses, the basement is between ~45-50F dirt (with insulation under the new slab, no less) and fully conditioned space above, and usually has less window area than fully above grade floors. Run those load numbers using a real load tool.

A 100K combi boiler isn't enough for reasonable hot water service, barely keeping up with just one full flow shower in the dead of winter. But a 100K boiler + indirect is overkill for this house. Assuming a heat load (all-in, basement + attic included) of 50K in the "after upgrades" version of th house, a boiler wiht 1.4x 50K= 70K would be more than enough for both heat and hot water. Properly set up, an 80K condensing boiler would heat a 50 gallon indirect in less than half the time of a standard 50 gallon gas water heater, a short enough time that the house won't lose even 1F in indoor temperature when giving priority to the indirect on the coldest hour of the year.

I've done the cals for the basement and attic at delta of 70, but I used my spreadsheet method. I am used to it and appreciate the ability to see all the cals and make changes on the fly to text certain options and double check work. I got the following results:

Basement 17.9K (11' ceilings and walk-out - above grade -for half of the wall. About 315SF is uninsulated brick to keep exposed brick look inside and out for that portion of wall - which accounts for half heat loss.)

Attic 5.0K (once I drew floor plan of the attic I realized it was much less space due to knee walls retracting floor area).

I am pretty sold on the idea of one boiler plus indirect tank now. I have been looking at options. First choice is Viessmann 222-F, but these are out of stock everywhere. I like the design here, because of onboard tank allows peak delivery of hot water in perfect storm of three showers for at least 10 minutes, before reverting to tankless - which is rated at 3.3gpm. I believe this system would be best.

Since I need to look at stock items, I am looking at 89,000 BTU Output Knight High Efficiency Boiler w/ Fire Tube Heat Exchanger (Floor Mount) (NG). I would add a 50 or 80 gal indirect to this system. Does this seem like a good options?

I am still unsure about how to accomplish supply temperature to Cast Iron and to Radiant Floor. With a primary and secondary piping system I would need a buffer tank? Or hydronic separation could occur with closely spaced tees? Then I would need to mix supply water from boiler with return water to have correct supply temperature for each type? And also to achieve condensation (particularly for cast iron)?

I have eliminated the panel radiator from the design and replaced with a used cast iron radiator to simplify system to two types - cast and radiant floor. Although I think radiant basement floors, which are cast in slab, may take different supply temperature than radiant floor upstairs, which is under duroc and tile (about 1 inch of dense cementitious material).

Thanks for all the help here. It has had a huge impact on the way I have conceptualized my heating and hotter systems design!

S

 

[Dana]

BTW: My sleepy stupid-attack from yesterday: As I was waking up with a cup of coffee the ventilation numbers seemed WAY off (and they were!)

The ASHRAE multiplier is 0.03 cfm (not 0.3) per square foot of floor area, and the BSC multiplier is 0.01cfm (not 0.1) per square foot.

So instead of 190' x 0.3 cfm +(2x 7.5 cfm)= 72cfm for a master bedroom you'd be looking at 190' x 0.03 + (2 x 7.5 cfm)= ~21 cfm at ASHRAE levels, for a heat loss at a 70F delta of 70F x 0.018 x 21cfm x 60m/hr= 1588 BTU/hr, and at BSC rates it becomes 190' x 0.01 cfm +(2x 7.5 cfm)= 17 cfm, for a loss of 70F x 0.018 x 17cfm x 60m/hr= 1285 BTU/hr.

Your true infiltration might be somewhat higher than the ASHRAE ventilation prescriptive before air sealing & insulating, but probably lower than the BSC recommended ventilation rate after.

Shooting for "...a little leaky..." is stupid-on-a-stick. There is no guarantee that the leakage air is anywhere near an adequate amount of ventilation air to the places most needed, and the potential contaminants picked up on random unknown paths can be significant. In tightened up houses soil gases are often a large component of the infiltration air (or ventilation air when using exhaust-only ventilation schemes). It has to be a VERY leaky house to reliably hit ASHRAE 62.2 levels in every room, and a house that leaky has very poor control over heat & moisture flows within the house. In those houses the top floors can be warm while the bottom floors are drafty & uncomfortable in winter, and the air in the entire house becomes uncomfortable and unhealthy due to ultra low humidity levels.

Short of balanced HRV ventilation, a single continuously running bath fan rated at the whole-house ASHRAE or BSC rates and installing adjustable intake ports in rooms that need the ventilation most (like bedrooms, baths, kitchens). Installing the intake port (could be as simple as a 1" PVC pipe with a ball valve for adjustment & bug screen) to bring the air in directly under or behind the room radiator limits the sub-zero comfort factor problem. Passive ports (no bath fan) that rely on stack effect or wind pressures rarely work in leaky houses, but can still do OK in VERY tight house. More on ventilation schemes for tight(er) houses lives here (with links to other more detailed blog bits, some of which are behind pay walls, but GBA offers free limited duration trial subscriptions that give access to all content).

Using 72F and -7F as indoor & outdoor design temps is just putting a thumb on the scale. Code requires a minimum of 68F indoors at the 99% outside design temp, those are the most appropriate numbers to use. It's unlikely that your actual 99th percentile temperature bin is as cool as -7F, but give me your ZIP code and I'll see if I can look it up. (The design temp at Millinocket & Loring are both -9F, Lewiston's is -2F.)

Assuming a design temp of 0F, if you're using ASHRAE's 1.4x oversize factor to size the system it can fully heat the place to +77F when it's -17F outside, if that's what you want to do. By putting the thumb on the scale when running the load calculations you're also scaling the thumb too. It doesn't take too many of these types of biased inputs to the calculation to exceed 2x oversizing for the actual load after applying the 1.4x factor. A 2x oversize factor is only appropriate only if you're anticipating -70F or colder temperatures, temps not seen in central Maine since he last ice age. Stick to "the Manual" when running a Manual-J- it'll save you money on radiation & equipment, and usually delivers higher comfort to boot.

To get to the U-factor or R-value of a 2x4 wall you have to consider R-values of the framing fraction, but also add in the air films, not just the claddings. With balloon framing with full-dimension 2x4s you're looking at framing fraction of about 20% in at typical house after adding in the jack studs, window headers, etc. . At 4" the stud itself is R5, to which you add the sheathing & siding R, interior plaster R, and interior & exterior air films, which add up to about R7 for a plank sheathed clapboard house with plaster & lath interior, but stud edges are only 20% of the total surface area. For the rest of it the plaster & lath is about R0.5-0.75, the sheathing + clapboards about R1.5-R2. But there are three interior air films at R0.63 each (R1.89) , and an exterior air film good for R0.17 for about R2's worth in air films alone. Add that to a (conservative) R2 for interior & exterior claddings and you're at R4 for the remaining 80% of the wall area.

The higher R of the framing fraction improves the average R of the wall for an uninsulated wall, but when insulation is added into the cavities the cavity R becomes higher then the framing fraction R, thus the framing fraction lowers the average performance of the wall in an insulated wall. If you're going to just take WAG (rather than formally calculating the U-factors) call the uninsulated wall R4 (U0.25) average performance, and the cellulose insulated wall R10 - R11 (U0.09-ish).

More on calculating U-factors here. More here.

Or just guesstimate based on U-factor tables here and here and here.

 

[Maine Way]

BTW: My sleepy stupid-attack from yesterday: As I was waking up with a cup of coffee the ventilation numbers seemed WAY off (and they were!)

The ASHRAE multiplier is 0.03 cfm (not 0.3) per square foot of floor area, and the BSC multiplier is 0.01cfm (not 0.1) per square foot.

So instead of 190' x 0.3 cfm +(2x 7.5 cfm)= 72cfm for a master bedroom you'd be looking at 190' x 0.03 + (2 x 7.5 cfm)= ~21 cfm at ASHRAE levels, for a heat loss at a 70F delta of 70F x 0.018 x 21cfm x 60m/hr= 1588 BTU/hr, and at BSC rates it becomes 190' x 0.01 cfm +(2x 7.5 cfm)= 17 cfm, for a loss of 70F x 0.018 x 17cfm x 60m/hr= 1285 BTU/hr.

Your true infiltration might be somewhat higher than the ASHRAE ventilation prescriptive before air sealing & insulating, but probably lower than the BSC recommended ventilation rate after.

Shooting for "...a little leaky..." is stupid-on-a-stick. There is no guarantee that the leakage air is anywhere near an adequate amount of ventilation air to the places most needed, and the potential contaminants picked up on random unknown paths can be significant. In tightened up houses soil gases are often a large component of the infiltration air (or ventilation air when using exhaust-only ventilation schemes). It has to be a VERY leaky house to reliably hit ASHRAE 62.2 levels in every room, and a house that leaky has very poor control over heat & moisture flows within the house. In those houses the top floors can be warm while the bottom floors are drafty & uncomfortable in winter, and the air in the entire house becomes uncomfortable and unhealthy due to ultra low humidity levels.

Short of balanced HRV ventilation, a single continuously running bath fan rated at the whole-house ASHRAE or BSC rates and installing adjustable intake ports in rooms that need the ventilation most (like bedrooms, baths, kitchens). Installing the intake port (could be as simple as a 1" PVC pipe with a ball valve for adjustment & bug screen) to bring the air in directly under or behind the room radiator limits the sub-zero comfort factor problem. Passive ports (no bath fan) that rely on stack effect or wind pressures rarely work in leaky houses, but can still do OK in VERY tight house. More on ventilation schemes for tight(er) houses lives here (with links to other more detailed blog bits, some of which are behind pay walls, but GBA offers free limited duration trial subscriptions that give access to all content).

I can see it's important to consider ventilation at the same time as designing the heating system. I had not thought about this much. Houses in this area do not use dedicated ventilation systems. This may be because we have a lot of old and very old housing stock, with very few new builds. We open windows 3 seasons for ventilation. Not much need for A/C in summer. And winter we use a lot of heat. I am thinking the blower door test will tell me how leaky and if I need supplemental ventilation. But, it seems that in sizing the boiler, I should consider the heat loss due to ventilation.

Using 72F and -7F as indoor & outdoor design temps is just putting a thumb on the scale. Code requires a minimum of 68F indoors at the 99% outside design temp, those are the most appropriate numbers to use. It's unlikely that your actual 99th percentile temperature bin is as cool as -7F, but give me your ZIP code and I'll see if I can look it up. (The design temp at Millinocket & Loring are both -9F, Lewiston's is -2F.)

Assuming a design temp of 0F, if you're using ASHRAE's 1.4x oversize factor to size the system it can fully heat the place to +77F when it's -17F outside, if that's what you want to do. By putting the thumb on the scale when running the load calculations you're also scaling the thumb too. It doesn't take too many of these types of biased inputs to the calculation to exceed 2x oversizing for the actual load after applying the 1.4x factor. A 2x oversize factor is only appropriate only if you're anticipating -70F or colder temperatures, temps not seen in central Maine since he last ice age. Stick to "the Manual" when running a Manual-J- it'll save you money on radiation & equipment, and usually delivers higher comfort to boot.

My plan is to follow your advice here and use zero or -2 for the outside temperature. I should be close to Lewiston. I'm 04345. I am looking at this in two stages, such that when Basement and Attic are added (more heat load), at that time the improvements will be done (reduced heat load). So the boiler sizing should work out well at under 100k BTU.

To get to the U-factor or R-value of a 2x4 wall you have to consider R-values of the framing fraction, but also add in the air films, not just the claddings. With balloon framing with full-dimension 2x4s you're looking at framing fraction of about 20% in at typical house after adding in the jack studs, window headers, etc. . At 4" the stud itself is R5, to which you add the sheathing & siding R, interior plaster R, and interior & exterior air films, which add up to about R7 for a plank sheathed clapboard house with plaster & lath interior, but stud edges are only 20% of the total surface area. For the rest of it the plaster & lath is about R0.5-0.75, the sheathing + clapboards about R1.5-R2. But there are three interior air films at R0.63 each (R1.89) , and an exterior air film good for R0.17 for about R2's worth in air films alone. Add that to a (conservative) R2 for interior & exterior claddings and you're at R4 for the remaining 80% of the wall area.

The higher R of the framing fraction improves the average R of the wall for an uninsulated wall, but when insulation is added into the cavities the cavity R becomes higher then the framing fraction R, thus the framing fraction lowers the average performance of the wall in an insulated wall. If you're going to just take WAG (rather than formally calculating the U-factors) call the uninsulated wall R4 (U0.25) average performance, and the cellulose insulated wall R10 - R11 (U0.09-ish).

This is very interesting, and I had not considered the framing portion of rah wall. So, absolutely I should use R-4 then, which boost pre-improvment R value by 33%! Huge! I had not thought of how the framing inhibits insulation as well, once improvements are made. I will have to look at that too. Primarily the sizing is based on the final project, as long as the boiler can reasonably keep up in the meantime.

I feel more confident about relative heat loads among rooms as well as before and after upgrades. I plan to order 89,000 BTU Output Knight High Efficiency Boiler w/ Fire Tube Heat Exchanger (Wall Mount) (NG) and a an indirect hot water heater in the next couple days. This is a very big shift in mindset from the first design with 2 combi boilers! Ironically, the price difference in equipment (2 combi Weil-McLain 125k VS Lochinvar 89k - presumably better boiler - with a 40 gal indirect) is about 1000$ more! I am paying more for equipment with less capacity. And, the equipment takes more space, due to the indirect tank. But, presumably more efficient system and more consistent hot water...

Shawn

More on calculating U-factors here. More here.

Or just guesstimate based on U-factor tables here and here and here.[/QUOTE]

 

[Dana]

I can see it's important to consider ventilation at the same time as designing the heating system. I had not thought about this much. Houses in this area do not use dedicated ventilation systems. This may be because we have a lot of old and very old housing stock, with very few new builds. We open windows 3 seasons for ventilation. Not much need for A/C in summer. And winter we use a lot of heat. I am thinking the blower door test will tell me how leaky and if I need supplemental ventilation. But, it seems that in sizing the boiler, I should consider the heat loss due to ventilation.

I understand completely about the state of housing stock in Maine, as well as the seasonal variations. (my wife's extended family has a place in Old Orchard Beach, and some in-laws is currently rehabbing an old house in Bethel as a multi-season getaway place, (not that their regular house in Goose Rocks is a dump that needs escaping from.) During the summers the nighttime ventilation schemes for cooling often work for sensible heat (even in central Maine) but some weeks (like this week) that approach brings in substantial amounts of humidity. With the changing climate summertime outdoor dew points have been climbing over the past few decades- faster than the change in 1% outside design temperatures.

A ductless mini-split per floor running in "DRY" can do wonders for comfort and mold-control, or even one of the modulatingU-shaped Midea window-shakers (which have a "DRY" mode). The dew point temp in Augusta right now is 70F, which is pretty damned sticky, and the indoor dew points of a non-air conditioned house will be drier still. Comfortable & human-healthy dew points would be holding the line at 55F (= 50% RH @ 75F), an outdoor dew point that isn't going to be seen in your neighborhood for another week or so.

A blower door test only tells you the aggregate size of the hole, not where those holes are, and thus can't be relied upon for putting the ventilation where it is needed the most, let alone predict the health quality of the infiltration paths. Even leaky homes need ventilation to stay healthy from a human health & comfort as well as mold & rot perspective, even if it's intermittently used bath & kitchen fans. Once insulated it needs it more (to protect both house & occupants), since the sheathing and siding will be much cooler on average, spending much more time below the indoor air's dew point, with no empty stud cavities to dry into. Moisture accumulation in the sheathing via vapor diffusion from the interior is slow, but drying toward the interior is also slow.

It's fine to just make the place as tight as you can and see how the place fares, but have a plan for what to do if some rooms get stuffy or moldy. A few $ 10 AcuRite humidity & temperature monitors are good enough. If the indoor RH averages above 35% @ 72F in winter it increases the risk of mold in the structural sheathing. If it stays well below 30% RH @ 68F for weeks on end it's less comfortable and less healthy for the humans, so th optimal humidity band that works best for both humans & house is fairly narrow in January, much wider during the shoulder seasons & summer. Your nose can often tell you if the volatile organics or mold spore content are climbing, but it's not the best test. If you decide some rooms need it more than others, there are single-room ceramic core ductless HRVs out there (and some that work in pairs as well, that don't pressurize/depressurize the house), that work by changing the direction of air flow every minute or so. Doing every room in the house with those solutions is prohibitively expensive, but it's worth considering for bedrooms. Ducted solutions are cheaper but more work, usually require significant cutting into ceilings and walls, and would be worth considering on a full-gut rehab. But ventilation ducts are very small compared to heating/cooling ducts.

With antique clapboards with a century's worth of multiple coats of paint you can anticipate that the paint will fail due to the outward vapor pressure when the sun falls on higher moisture content wood with highly vapor retardent paint. When it's time to repaint, stripping as much of the loose stuff as possible and painting with a latex paint (or even more permeable stain) will do better than using alkyd paints. It'll need repainting or touch-ups every handful of years as more stuff flakes off, but only in rare instances will it be bad enough to warp & split the clapboards themselves. Using cellulose works better than fiberglass or rock wool insulation, since the cellulose shares the moisture burden (without loss of function), lowering the peak moisture content of the plank sheathing.

My plan is to follow your advice here and use zero or -2 for the outside temperature. I should be close to Lewiston. I'm 04345. I am looking at this in two stages, such that when Basement and Attic are added (more heat load), at that time the improvements will be done (reduced heat load). So the boiler sizing should work out well at under 100k BTU.

ZIP 04345 is less than 5 crow-miles from the Augusta airport, where the 99% outside design temp is +1F, and more than 10 miles from Lewiston. If you want to split the difference go ahead and use 0F as a design temp, not -2F.

I feel more confident about relative heat loads among rooms as well as before and after upgrades. I plan to order 89,000 BTU Output Knight High Efficiency Boiler w/ Fire Tube Heat Exchanger (Wall Mount) (NG) and a an indirect hot water heater in the next couple days. This is a very big shift in mindset from the first design with 2 combi boilers! Ironically, the price difference in equipment (2 combi Weil-McLain 125k VS Lochinvar 89k - presumably better boiler - with a 40 gal indirect) is about 1000$ more! I am paying more for equipment with less capacity. And, the equipment takes more space, due to the indirect tank. But, presumably more efficient system and more consistent hot water...

The Lochinvar KHB/WHB-085N has ~79K of DOE output which is perfectly adequate for 19 out of 20 homes in Maine (not the coastal pleasure palaces of the ultra-rich, but real-peoples' homes), and I would expect it to be a good fit for your heat & hot water loads. The fact that it's minimum input is 8500 BTU/hr (min-out = ~8K) means that it can handle some fairly small zones at condensing temps without short cycling, especially zones with a reasonable amount of thermal mass (water volume) in the radiators. With low-mass fin-tube baseboard you'd need at least 35-40' of baseboard to keep short cycling risk well bounded. But if you size the radiators proportional to the room loads and maybe add some TRVs for tweaking individual radiator temps it's pretty easy to zone it a whole floor at at time.

 

[Maine Way]

I understand completely about the state of housing stock in Maine, as well as the seasonal variations. (my wife's extended family has a place in Old Orchard Beach, and some in-laws is currently rehabbing an old house in Bethel as a multi-season getaway place, (not that their regular house in Goose Rocks is a dump that needs escaping from.) During the summers the nighttime ventilation schemes for cooling often work for sensible heat (even in central Maine) but some weeks (like this week) that approach brings in substantial amounts of humidity. With the changing climate summertime outdoor dew points have been climbing over the past few decades- faster than the change in 1% outside design temperatures.

A ductless mini-split per floor running in "DRY" can do wonders for comfort and mold-control, or even one of the modulatingU-shaped Midea window-shakers (which have a "DRY" mode). The dew point temp in Augusta right now is 70F, which is pretty damned sticky, and the indoor dew points of a non-air conditioned house will be drier still. Comfortable & human-healthy dew points would be holding the line at 55F (= 50% RH @ 75F), an outdoor dew point that isn't going to be seen in your neighborhood for another week or so.

If you know Old Orchard and Bethel, then you have a very good idea of Maine. Cooling is used by some in summer, and my bed and breakfast has AC, which are mostly always on site the guests don't pay the electric bill. So, that does help with moisture. I am beginning to warm up to including some means of controlled ventilation. The mini-split seems like a large expense to add to the budget, but it may accomplish multiple HVAC goals. Further down the road, when the building is divided, I would need to have mini splits by unit, so I would be looking at multiple compressor units, or at least to safeguard the design to change that out with homers to electric panels and coolant lines planned for each unit. Minimum at this phase is to have a design in place and know how it would be accomplished if it makes it into the project.

A blower door test only tells you the aggregate size of the hole, not where those holes are, and thus can't be relied upon for putting the ventilation where it is needed the most, let alone predict the health quality of the infiltration paths. Even leaky homes need ventilation to stay healthy from a human health & comfort as well as mold & rot perspective, even if it's intermittently used bath & kitchen fans. Once insulated it needs it more (to protect both house & occupants), since the sheathing and siding will be much cooler on average, spending much more time below the indoor air's dew point, with no empty stud cavities to dry into. Moisture accumulation in the sheathing via vapor diffusion from the interior is slow, but drying toward the interior is also slow.

It's fine to just make the place as tight as you can and see how the place fares, but have a plan for what to do if some rooms get stuffy or moldy. A few $ 10 AcuRite humidity & temperature monitors are good enough. If the indoor RH averages above 35% @ 72F in winter it increases the risk of mold in the structural sheathing. If it stays well below 30% RH @ 68F for weeks on end it's less comfortable and less healthy for the humans, so th optimal humidity band that works best for both humans & house is fairly narrow in January, much wider during the shoulder seasons & summer. Your nose can often tell you if the volatile organics or mold spore content are climbing, but it's not the best test. If you decide some rooms need it more than others, there are single-room ceramic core ductless HRVs out there (and some that work in pairs as well, that don't pressurize/depressurize the house), that work by changing the direction of air flow every minute or so. Doing every room in the house with those solutions is prohibitively expensive, but it's worth considering for bedrooms. Ducted solutions are cheaper but more work, usually require significant cutting into ceilings and walls, and would be worth considering on a full-gut rehab. But ventilation ducts are very small compared to heating/cooling ducts.

I think the wait and see approach is tempting. Although, summers here are humid and everything you have touched on does make sense. We are closed up now, although it was a 50% gut, mostly ceilings, and now we are moving toward finishes. There must be through-wall units for venting that require little destruction, although they would need a power source.

With antique clapboards with a century's worth of multiple coats of paint you can anticipate that the paint will fail due to the outward vapor pressure when the sun falls on higher moisture content wood with highly vapor retardent paint. When it's time to repaint, stripping as much of the loose stuff as possible and painting with a latex paint (or even more permeable stain) will do better than using alkyd paints. It'll need repainting or touch-ups every handful of years as more stuff flakes off, but only in rare instances will it be bad enough to warp & split the clapboards themselves. Using cellulose works better than fiberglass or rock wool insulation, since the cellulose shares the moisture burden (without loss of function), lowering the peak moisture content of the plank sheathing.

The plan os to strip off the asbestos and strip off the old clapboards, and reside using fiber cement. It hold paint well, only requiring new paint every 25 years (although colors do fade). One side of the building, due to the tall basement, is 34' off the ground at the eave. We would like to aim to reduce maintenance and at the same time take advantage of the stripped house to blow all cavities.

ZIP 04345 is less than 5 crow-miles from the Augusta airport, where the 99% outside design temp is +1F, and more than 10 miles from Lewiston. If you want to split the difference go ahead and use 0F as a design temp, not -2F.

Roger that. Sounds like you were spot on for outside design temp.

The Lochinvar KHB/WHB-085N has ~79K of DOE output which is perfectly adequate for 19 out of 20 homes in Maine (not the coastal pleasure palaces of the ultra-rich, but real-peoples' homes), and I would expect it to be a good fit for your heat & hot water loads. The fact that it's minimum input is 8500 BTU/hr (min-out = ~8K) means that it can handle some fairly small zones at condensing temps without short cycling, especially zones with a reasonable amount of thermal mass (water volume) in the radiators. With low-mass fin-tube baseboard you'd need at least 35-40' of baseboard to keep short cycling risk well bounded. But if you size the radiators proportional to the room loads and maybe add some TRVs for tweaking individual radiator temps it's pretty easy to zone it a whole floor at at time.

One of the reasons I was attracted to this model boiler is the versatile turndown ratio. As you say, flexible for smaller zones. I am going with cast iron baseboard and radiant heat as the two emitters on the project. This simplifies the design (I hope) to have only two types. I've avoided fin tube or panel radiators since they don't do as well with thermal mass, have higher supply temperature requirments, and don't have the comfort of the added company of radiated heat energy.

I think zoning a whole floor would be under consideration, if I did not have different emitters on each floor, and if the plan was not eventually to separate living units by east and west, each with its own stair. So, I am really down to smaller zones. But, that will be the interesting challenge in the design...

Shawn