Screwed by Sandy: Need a new boiler/domestic hot water heater, might as well upgrade?

Hi Forum!
I'm excited to be posting here for a first time but sad it's under such circumstances.

I'm looking for advice from a range of professionals as to what to do. Our boiler (63k BTU New Yorker) was completely submerged as were all the controls. Also our 40 gallon hot water heater was submerged (both with salt water). Both were natural gas fired. We also had to tear up carpet (a good time to remodel to hardwood floors) in two of the rooms. The upstairs previously was on one zone and the basement on a separate zone. While we install new floors I figured it would be good to do radiant heating (I'm sure I can install that part myself). Since the whole thing needs to be replaced, should we go high efficiency? Combo unit? Indirect hot water heating? Other? Sky's the limit I suppose? I had one plumber tell us we should upgrade the size to 96k BTU for better performance but the more I read about these systems I'm not so sure that's a good idea. We have 1000 sq ft on main floor with three sides (~95 linear feet of exterior walls and one party wall with a total of ~100 sq ft of windows. In basement we have about 600 sq ft with 16" thick concrete foundation. He justified the bigger boiler by telling me (and 14 other condo owners) that it should be about 50 BTU/sq foot which would give us a need for around 80k BTU. I feel like this might be high based on what I've read here. Thoughts?

Exhaust venting shouldn't be a problem since it's close to an exterior wall if needed. Also, would love to get units off ground as much as possible in case of another 'incident'. There are two bedrooms that I'm putting the radiant in and the living room still has the baseboard (will upgrade living room to radiant when the floor starts to buckle and needs to be replaced/kitchen remodel) so in total it'd be 4 zones (2 radiant + 2 baseboard) (eventually 3 radiant + 1 baseboard). I was planning on using 1/2" PEX in loops of around 300 ft for the bedrooms. Strips of 3/4" plywood over 1/4" foam insulation with concrete filling in around the PEX.

If somebody could help me design a system I'd be willing to pay for that service if it's from somebody I trust but it needs to happen sooner than later as currently we have no heat and hot water up here in NYC and winters'a'comin.

I appreciate the help!

-Sandy Survivor

Definitely high efficiency. Take a look at buderus,lochnivar,triangle tube and others.

Sorry to hear about the flood. We design hydronic heating systems and specialize in condensing boilers.

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There are lots of threads that can guide you on how to determine how much heat your old boiler was providing. I have no idea why, if your old boiler was heating the place, the guy thinks a bigger one is now necessary! Often, in a condo, you have some common walls, minimal exterior walls, and therefore a low heat load. An indirect should not be considered as part of the heating load, and you should NEVER upgrade the size of the boiler for its use unless you run something like a spa that is constantly using lots of hot water...the IWH is configured as a priority zone so that it gets ALL of the heat from the boiler when it needs it. Unless you live in a drafty barn, you'll never notice it's stopped heating the space while it rewarms the WH. Once the WH has come up to temp, things return to normal space heating. I wouldn't be surprised if you couldn't use a (probably much) smaller boiler. You'd need your last winter's gas bills along with those from the summer to figure out what part of that was water heating verses the old boiler. then, the heating degree day info and you can then figure out how much heat you were using. Try to find a boiler that is that size, which will almost certainly be still a little big - the closer you can get without going under, is what you really want.

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Originally Posted by jadnashua

There are lots of threads that can guide you on how to determine how much heat your old boiler was providing. I have no idea why, if your old boiler was heating the place, the guy thinks a bigger one is now necessary! Often, in a condo, you have some common walls, minimal exterior walls, and therefore a low heat load. An indirect should not be considered as part of the heating load, and you should NEVER upgrade the size of the boiler for its use unless you run something like a spa that is constantly using lots of hot water...the IWH is configured as a priority zone so that it gets ALL of the heat from the boiler when it needs it. Unless you live in a drafty barn, you'll never notice it's stopped heating the space while it rewarms the WH. Once the WH has come up to temp, things return to normal space heating. I wouldn't be surprised if you couldn't use a (probably much) smaller boiler. You'd need your last winter's gas bills along with those from the summer to figure out what part of that was water heating verses the old boiler. then, the heating degree day info and you can then figure out how much heat you were using. Try to find a boiler that is that size, which will almost certainly be still a little big - the closer you can get without going under, is what you really want.

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Thanks for the replies do far. We are in a condo yes but an end unit so more exterior/non-shared walls and a ground floor unit which is bigger than all others because of the basement and questionable insulation in ceiling to second (of 3) floor. All units in condo originally had the same size boilers and since we only closed and moved in in June we don't know what the winter is like yet...

You think combo unit or indirect or other for go water and why?

Every space heating job, be it renovation or new construction start with a Manual 'J' heat load analysis. If you don't know the load that the condo presents, you don't know anything. Once you have a proper heat load you then can make informed decisions about heating space and hot water with one combi appliance. When designing heating systems for condominiums we most often use condensing water heaters with radiant floors, walls and ceilings and occasionally even through in a fan coil if we have to. There are few condos that are big enough to justify the smallest gas-fired boilers made.

My personal experience with a combo was not good, but then that's one of millions that are in use. If you live there long enough, you'll probably live to curse a combo. They require more maintenance, and tend to cost more to run verses the use of an indirect.

Your heat load is probably less than 25KBTU, but that's just a guess. The only way to tell is to analyze what you have...WAG based on square feet will always oversize unless you live in a drafty warehouse. Often, radically oversize.

Condo builders like consistency - buy 50 units the same, get a great price, teach one guy to install them, and not worry about the efficiency as long as it works. As you've noted, not all of the units are the same in configuration, exposure, location or sizing...therefore, it is highly doubtful they each need the same sized unit. If what you have heated the unit for 6-years, there's no way you need a larger one. Larger both costs more to buy, but also to run. The most efficient is the one closest to what you need. Ideally, it would run 100% of the time when in the middle of a cold snap - heat that goes on and off is not anywhere as comfortable as that that is running all the time. Each on/off cycle wastes heat and hits efficiency. A larger unit than needed will cycle more, wear out sooner, and cost more to operate.

It is important to size the thing, and a WAG doesn't cut it!

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Originally Posted by BadgerBoilerMN

Every space heating job, be it renovation or new construction start with a Manual 'J' heat load analysis. If you don't know the load that the condo presents, you don't know anything. Once you have a proper heat load you then can make informed decisions about heating space and hot water with one combi appliance. When designing heating systems for condominiums we most often use condensing water heaters with radiant floors, walls and ceilings and occasionally even through in a fan coil if we have to. There are few condos that are big enough to justify the smallest gas-fired boilers made.

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I called you guys and left a message last night. Hoping to talk to somebody sooner than later about some stuff.

BadgerBoilerMN tells it true when he says, "There are few condos that are big enough to justify the smallest gas-fired boilers made.".

The notion that you should bump it up to a 96KBTU unit is insane. If your heat load really adds up to 50 BTU/ft @ +15F (the 99% outside design temp for much of L.I. & NYC) it means you need to close the doors or put glass back in the windows (you were gonna do that anyway, right? :-) ) Even on older housing it's pretty common to see true heat loads under 15BTU/ft, or even under 10BTU/ft. But no "BTU/ft" rule of thumb has any accuracy- heat loss is about exterior surface area, U-factor/R-value, and air leakage, which varies quite a bit, and is not a ratio of the floor area of the conditioned space.

Micro-zoning an already small heat load will cause modulating condensing boilers to short-cycle into low-efficiency and an early grave. A condensing HW heater based solution is self-buffering and can't short-cycle. It would usually work for radiant zones, but may prove a problem for baseboard zones without upgrading the heat emitters. This is not something suitable for a "design-by-web-forum" approach.

It's also true that in a coastal NY/NJ climate heating one more more zones with an inverter-drive ductless mini-split heat pump can make sense (even with low-cost gas and high-priced electricity), and has the additional benefit of being able to air-condition with the same equipment. It's not as luxuriant-cushy as radiant floors, but more comfortable than heating with fin-tube baseboard or ducted hot air.

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Originally Posted by Sean Jacobs

I called you guys and left a message last night. Hoping to talk to somebody sooner than later about some stuff.

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Better to start with an email. I design and install for a living, this is my hobby...:-).

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Originally Posted by Dana

BadgerBoilerMN tells it true when he says, "There are few condos that are big enough to justify the smallest gas-fired boilers made.".

The notion that you should bump it up to a 96KBTU unit is insane. If your heat load really adds up to 50 BTU/ft @ +15F (the 99% outside design temp for much of L.I. & NYC) it means you need to close the doors or put glass back in the windows (you were gonna do that anyway, right? :-) ) Even on older housing it's pretty common to see true heat loads under 15BTU/ft, or even under 10BTU/ft. But no "BTU/ft" rule of thumb has any accuracy- heat loss is about exterior surface area, U-factor/R-value, and air leakage, which varies quite a bit, and is not a ratio of the floor area of the conditioned space.

Micro-zoning an already small heat load will cause modulating condensing boilers to short-cycle into low-efficiency and an early grave. A condensing HW heater based solution is self-buffering and can't short-cycle. It would usually work for radiant zones, but may prove a problem for baseboard zones without upgrading the heat emitters. This is not something suitable for a "design-by-web-forum" approach.

It's also true that in a coastal NY/NJ climate heating one more more zones with an inverter-drive ductless mini-split heat pump can make sense (even with low-cost gas and high-priced electricity), and has the additional benefit of being able to air-condition with the same equipment. It's not as luxuriant-cushy as radiant floors, but more comfortable than heating with fin-tube baseboard or ducted hot air.

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I finally did my own heat load calculation! Screw the software, too complicated for me... and expensive. Good old pencil and paper with my engineering background put to use! :-) I got a little over 19k BTU/hr on the main floor (about 1100 ft^2) and a little over 18k BTU/hr in the basement (about 600 ft^2 with some conservative assumptions about below grade temperatures and lack of floor insulation. I do plan on insulating more down there which should cut it down to closer to 8k BTU/hr).

It looks like we'll be tearing up the floor in the living room to match the bedrooms in the next 6 months so we plan on a full radiant conversion at that point. Also plan on raising the basement floor with foam insulation so will probably do radiant down there as well! NYC Rapid Repairs program amazingly installed a brand new 40 gallon gas water heater and a 77kBTU cast iron weil-mclain boiler! They are just doing the bare minimum to get us up and running so it's up to me to make the system how I want it. What a project!

The boiler is a bit over sized so once I get all the radiant rooms squared away I may consider a buffer tank(boiler buddy?) if needed, or at least a low loss header? I imagine these could still be useful even though it's not a mod/con, right? Any advice on a good manifold? So many to choose from and they all look nice...

As for the radiant floor installation I have concerns for future flooding. How does this sound... Tear floor down to the plywood subfloor (on steel joists). glue down 1/2" or 1" foam insulation with metallic backing facing down. They lay sleepers 4" x 3/4" cement fiber board (or something plastic) (to resist future mold growth under floor if flooding). Lay PEX on insulation between sleepers then (after pressure testing w/ pressure held) fill screed around PEX and trowel it so it's level with the sleepers. I want to make this so i don't have to worry about anything growing inside the floor. I'm a little hesitant to do concrete on the whole floor because i'm afraid I couldn't keep it level for the engineered floor to put on top of it.
How does this sound, any advice?

Always thanks!

That combined heat load of 37K sounds considerably oversized for a condo that size @ +15F unless you were were using the all time record low temp as the design temp, an interior temp of 78F, or included a huge ventilation rate.

What U-factors were you using for the above-grade walls, roof, above-grade foundation, and below-grade foundation?

Assuming an interior temp of 70F, and a 99% outside design temp of 15F that's a 55F delta-T

With 100 square feet of window, assuming sub-code double-panes or old double-hungs you'll have a U-factor for windows of ~0.5, so the total window losses would b

100 x 55 x 0.5= 2750 BTU/hr

With 600 square feet of 16" exposed poured concrete foundation the U-factor is a bit under 1, but lets call it 1 for the ~100-150' of above grade foundation, but below grade you also have the insulative value of the soil below grade, so for below-grade you shouldn't count on anything more than 0.3, and a soil temp no colder than the wintertime average, which eyeballing the Weatherspark.com cursor for NYC for the months of December through February is ~35F. Assuming you fully condition it to 70F you have a delta-T of only 35F (at most) for the below-grade portion, 55F for the above grade:

Above grade: 150' x 55 x 1= 8250
Below grade: 450 x 35 x 0.3= 4725

Total basement: 12,975 (< and that's a generous margin over reality- it's probably under 10K even with wet heat-conductive soil, less if you don't heat it to 70F.)

Assuming you have 20' of wall from the foundation to the upper floor ceiling, and 2x4 fiber-insulated construction (or brick veneer with 2" of rigid foam, no fiber) the total area is (95 x 20)-100= 1800 square feet of ~U0.1 wall.

1800' x 55F x 0.1= 9900 BTU/hr.

Assuming ~ 500 square feet of upper floor ceiling with R30 blown or batts you have a U-factor of about 0.04 for:

500 x 55 x 0.04= 1100 BTU/hr

Add it all up and all you get is 26,725 BTU/hr.

If you have the draftiest condo in NY you might break 30K, but even with infiltration you're not going to hit 37K. Reality is probably less than 25K, but you'd be able to determine that if you have a mid-winter gas bill and the meter reading dates to run a therms/heating degree-day calc on.

And if you do a modest amount of insulation on the basement walls (eg: an inch of rigid EPS trapped to the foundation by a studwall insulated with unfaced batts, or 2-2.5" of EPS held by furring through screwed to the foundation with TapCons, to make it more flood-resiliant than a batt solution) you'd be under 20KBTU/hr.

With a high mass boiler 3x oversized for the heat load you may well be short-cycling- it really depends on the amount of heat emitter you have going on the smallest (radiation-wise) zone. Turn down thermostats on all but the smallest zone (crank that one way up), time the burns, see how it's doing. If you're not getting 5 minutes/burn out of it you may want to buffer it sooner than later.

BTW: With the above-the-subfloor installations go with 3/4" foam & sleepers and half-inch PEX with sheet metal heat spreaders. Do NOT use foil faced goods for the foam- the foil has no thermal benefit in this application and will just serve as a moisture trap. With XPS (pink/blue/green whaddevah) you'll get almost R4 out of it, with cheaper EPS board (recommended) it's only about R3, but neither is sufficient for zone isolation- you'd stll have to put something between the joists. If the basement joists are open you could use unfaced 2" EPS (R8) glued to the subfloor with hazenut-sized blobs of foam board adhesive on a 12-16" grid, which would be able to dry reasonably quickly after a flood. Plan-B would be fiberglass batts snugged up to the subfloor (facer down is OK since it's facing conditioned space), but you'd have to rip it out and re-do in the event of a flood.

Fiber cement board nailer-subfloor isn't really very water tolerant. I doubt you'd be able to save the nailer-deck in the event of another flood anyway, and unless there's another flood the mold hazard is low, since it's inside conditioned space. Since it's fully supported between the sleepers with foam you can use half-inch plywood or OSB sheathing with a ship-lap edge rather than full thickness subfloor type goods, as long as you promise to nail/staple only over/into the sleepers.