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Thread: May need to replace boiler – What with?

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    DIY Junior Member Heating in Colorado's Avatar
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    Default May need to replace boiler – What with?

    I am new at this an am looking for some help and advise.

    I have a Colorado 80526 2 story plus basement home which I built in 1985, all original. It is heavily insulated including triple glazing. It currently has 4 zones controlled with zone valves plus the current gas boiler does DHW. It was built to have good passive solar gain and on the current system and only uses 530 therms /year in including a gas dryer and grill. I have calculated it uses 30 therms/ mo. in summer. It requires heat only 5 month, with the maximum used in past five years 125 therms in January and averaging 74 therms per month for entire heating season. There is only my wife and I living in the house and it has 3 bedrooms with a tub and two showers. Our current gas rates are about .08 / therm plus a $10 monthly fee. We hope to be in here for many more years.

    All current radiation is slant fin; I have the separate zone information. One zone is in a shop which is heated only when the area is used, which adds a sudden load of 40 degree water upon initial start up in the return. This shop has been a part of the system for only 15 years.
    The system that it has been running on is a Heatmaker. This has developed a drip from the 12 gallon tank and I assume the boiler will need replaced. For the past 25+ years the basement has been kept at 72, all winter (often turned to 74 when 10 or below outside) and the 1st floor heat comes on only when the outside temperature drops enough, to come on at 70, (occasionally to 72 in evening) the 2nd floor is kept at 62 -66 and then comes on only when it is really cold, possibly below 10 and / or very windy.

    I am a novice on this compared to many very experienced contractors. I am also concerned with spending a small fortune to “save energy” on a house that has cost so little for DH & DHW. I have looked around some at on demand DHW and see a lot of complaints. However, I also have been reading the forums and see many problems from a lot of Mod Coms. I am trying to be informed on what is the best way to go. Is a mod/com too expensive for the small saving I should expect? I expect I will need a side arm heater, unless there is a better idea. What about size, the Heatmaker is 120KBTU input and has always been plenty big.

    My requirements seem simple, but I am looking for any input. Thank you
    It must be rim joist vented. Low cost to operate. Limit up front cost, house currently only cost $160 / yr to heat & $130/ yr for DHW, $60 / yr for dryer & grill. I have more detail that can go here too.

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    In the trades Dana's Avatar
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    Every good heating system design starts with a room-by-room heat load calculation based on realistic indoor temps and the 99% outside design temp for your location. If zip 80526 Fort Collins that design temp is +1F in town, but if you live in the hills subtract 3F per 1000' above 5000'. That information will determine how much burner you actually need.

    In a passive solar house it's not possible to determine the heat load based on fuel use. The information you would need for the rough cut is the "whole-wall" R-value and area of exterior wall in each room, the "whole-assembly" R-value of the roof/attic assembly (where appropriate) and the ceiling area, and the window U-factors & area. If you set up a spreadsheet with the wall/ceiling/window area & U-factor of the windows, with the wall & attic construction & R-values we can cook up reasonable whole-assembly R values to generate a U-factor for the walls & upper floor ceilngs.

    The basic calculation of the heat load is:

    U-factor x temperature difference x square feet= BTU per hour.

    Add up the numbers for wall/window (and door)/ceiling for each room to come up with a raw heat load for the room. Add all of the room loads on each zone to come up with the zone load, and add up the zones for a whole-house load. Since the shop zone is intermittent use only, keep it separate, or only calculate it with a 45F indoor temp (or whatever temp you keep it at when not in use.)

    To fine-tune it you'd have to add a fudge-factor for infiltration/ventilation rates, and subtract out interior heat sources (250BTU/hr per sleeping human, 150BTU/hr per refrigerator, etc.), but in a tight passive solar house using just the raw conducted loss numbers should be close enough.

    Then you will need to measure up the linear feet of SlantFin baseboard in each zone. The ratio of heat load per foot of baseboard will determine the water temp required to deliver enough heat to cover the load.

    With the heat loads and water temp requirements then (and only then) is it possible to come up with appropriate & reasonable heating equipment suggestions for meeting that load (and how to set it up.)

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    Dana,
    Thank you very much for that information. I will put those numbers together.

    I know the wall and upper ceiling R factor information. I am not sure on the glass, it is thermopane dubble hung windows 3" trapped air plus storm. Can I use .2 safely for the U factor of the windows? I will put that information together and come back with it. I already have the linear feet of slantFin in each room as well as in total zones on a speadsheet.

    Your comment on the solar making the fuel consumption numbers ineffective, has allowed me to stop working on that chart at this time. Thanks, that makes sense.

    I started this quest because the first contractor came to the house and without having any of the information you have requested here, spent 20 minutes in the house and with no consideration for anything gave me his bid for a mod con. I knew then, I needed to learn newer more current information. Thanks for giving me and I am sure other a direction to look.

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    In the trades Dana's Avatar
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    1980s vintage clear glass double panes on their own have U-factor of ~0.5-0.6. Adding a clear glass pane 3" away brings that down to U-0.35-0.4 or so. Without any low E coatings on either the double-pane or the storm window glazing, assume it's something like U-0.38.

    To hit U-0.2 requires 3 panes and multiple low-E coatings, and they're pretty pricey. In a passive solar home you wouldn't normally want U-factors that low, since the low-E coatings cut severely into solar gain. At about U0.35 sealed double panes with just a single surface of low-E on one of the surfaces inside the sealed portion will usually have a fairly optimal gain/loss characteristic, gaining considerably more energy during wintertime daylight hurs than they lose overnight. Clear glass U-0.5-0.6 double panes have higher gain than a U0.35 window but they lose a lot more too.

    When calculating U-factors for walls/ceilings you can't use just 1/R of the center-cavity insulation value of a studwall. The thermal bridging of the framing is significant, but the sheathing & siding adds some too. eg: A typical 2x6 16" studwall has a framing fraction of ~25% (1/4 of the area is thermally bridged by ~R6.5 studs, plates headers, etc.). With R20 cavity fill and an R1 allowance for the combined sheathing/siding/gypsum the "whole wall" R comes in between R13 & R14, with a U-factor of ~0.075 rather than (1/R20=) U0.050.

    Attics and cathedral ceilings have lower framing fractions than walls, and sometimes the joists are thermally broken with insulation deeper than the joist depth.

    Bottom line, to come up with realistic U-factors for walls & ceilings we'd need a description of the whole assembly, from the interior paint to the exterior paint. Passive solar homes tend to be built & insulated differently from standard code-min construction, so it takes a more careful analysis to have any accuracy at all. If stick-built, the stud/rafter/joist spacing makes a difference too.

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    Dana
    Thank you on the glazing numbers and information. These are clear glass, no E coating, it sounds like I will be able to use U-0.38 for most of the windows, which are all the same construction as well as the same size. However I do have a few fixed windows which at the standard 80’s triple glazing with maybe ½” between the layers of glass. I have then added a decorative cut class in a fixed framed with 1" of air inside of that and then an additional layer of glass for protection inside of that making a total 5 layers of glass wit 2 - 1" layers of trapped air. How do I figure the U factor on that? I have two Velux skylights which show this value: U factor = .44, then there is a layer of fixed glass mounted in the opening with 6” of trapped air space. How do I figure that total U factor?

    As I recall the foil backed urethane foam boar used on the entire house had printed on it that the R value was 2.38, can that be right?

    Here is the exterior wall construction: Stick built 16” o.c., 2x6, 8’ ceilings. starting with interior paint/ ½” gypsum board/ 3 mill full vapor barrier/ framing w R19, non backed Owens Corning Fiberglass fill/ outside surface is covered with 1/2” urethane foil double faced board. US Steel siding with no additional backer insulation. All seams of foil board are sealed, all windows, doors electrical boxes and plates had urethane foam seal added to slow infiltration.I am not sure how to figure this total wall when the urethane covers the outside of the studs.

    Here is the 2nd floor ceiling construction: No cathedral ceilings in the house area. Trusses made of 2x4 constructions, 24” o.c., starting with interior paint/ ½” gypsum board Blown in Owens Corning small all fiberglass cubes to R 40 when new. Added on top across the direction of the trusses with additional filling at truss bracing was R19 Owens Corning with no backing. The area has adequate ventilation with a power vent for summer use.

    There is a 4’ wide front & back roof on the 1st floor that makes up unheated area above. Here is the construction: Sick built 2x6 constructions, 24” o.c., starting with interior paint/ ½” gypsum board bats fill the area as much as possible to allow ventilation above. That makes it first R19 covering the entire area, then the upper half another layer of R19. So half is R19 and half of the area is R38. This total length is 38’ which will need to be included in the 1st floor planning. I think I can figure this okay.

    The finished basement walls are ; paint ½” gypsum board, 1-1/2’ urethane with 2x2 16”o.c. striping then 8” poured concrete, on the exterior all basement walls, they are covered with 2” of urethane. The rim joist is R19 Owens Corning bats.

    The unfinished basement walls ; do not have the interior insulation, 2x2 nor drywall, so that will be easy to figure, but mostly subsurface with I suppose a constant of about 55 degrees below 2 feet.

    It has been a while since I have figured any of this stuff! Thanks for your help.

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    I have calculated the total wall R values for all of the combinations in the house. I used the charts from www Colorado energy.org which was much easier to use from this site: http://www.allwallsystem.com/design/RValueTable.html

    I assumed that since near 10% of the wall is stud in a 16” o.c. application the built R value of the wall was 90% of the Total Wall R value and that 10% of the wall was the R values where the studs are in the wall. I came up with the average. Now I will calculate the ceilings the same way, unless someone gives me a reason to believe that that this is not correct. This gave the worst U value in the house as .042845 in this solar assisted home. No considerations are made for solar gain.

    I now need a program that allows me to insert all of the information for the walls, windows etc to arrive at the totals of each room and then the house. Any recommendations?

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    In the trades Dana's Avatar
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    Quote Originally Posted by Heating in Colorado View Post
    I have calculated the total wall R values for all of the combinations in the house. I used the charts from www Colorado energy.org which was much easier to use from this site: http://www.allwallsystem.com/design/RValueTable.html

    I assumed that since near 10% of the wall is stud in a 16” o.c. application the built R value of the wall was 90% of the Total Wall R value and that 10% of the wall was the R values where the studs are in the wall. I came up with the average. Now I will calculate the ceilings the same way, unless someone gives me a reason to believe that that this is not correct. This gave the worst U value in the house as .042845 in this solar assisted home. No considerations are made for solar gain.

    I now need a program that allows me to insert all of the information for the walls, windows etc to arrive at the totals of each room and then the house. Any recommendations?
    Were you walls just infinitely long studs, with no jack studs, king studs, bottom plates,doubled-up top plates, window & door headers & framing etc, yes, you'd be at about a 10% framing fraction. In the real world walls have finite height, and they have windows & doors & wall lengths that don't align perfectly with top & bottom plates. This has been surveyed to death by building designers for decades- typical framing fractions for 16" o.c. spacing average around 25%. They can hit 30% or higher where mid-wall fire-blocking or seismic reinforcement is required, maybe as low as 20% for balloon framing with the window & door size & placement are carefully selected to align with the standard stud spacing, and only single thickness plates & headers used. Using a 10% framing fraction your heat loss number will be wildly optimistic. Unless you've added it all up from the original blue prints, assume 25%- it'll be close enough.

    If you use an Excel or Open Software Foundation spreadsheet tool, set up a room by room blocks of cells to do the numbers something like:

    Kitchen

    __________ U-factor _x_ area__x__design delta-T_=_heat loss

    Windows: ____0.38_____10.5'_______68F_________271 BTU/hr

    Doors:_______0.50_____22'_________68F_________748 BTU/hr

    Wall: ______0.057_____127'_________68F________492 BTU/hr

    Ceiling:__ __0.023_____154'_________68F________241 BTU/hr

    Room total:_________________________________1752 BTU/hr

    Dining room (etc.)

    Then add up the subtotals of for all the rooms in each zone, and the ratio of BTU/foot of baseboard for the zone. Add up the heat loads of all the zones to come up with the whole-house total heat load. (Assume the shop zone to have a 45F interior temp to account for the intermittent use aspect.)

    Calculate the "whole-wall" R values carefully (or give me your stackup and I'll hand off something close enough), and use 1/R for the U-factor. Do a similar calc for the attic/ceiling to come up with a U-factor for the upper floor ceilings.

    When you have the whole house load and the ratio of BTU/foot-hour for the baseboard, the range of solutions can be weighed.

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    Dana
    I understand the fact that the wall is not really 10% stud when just simply plates, headers, jack studs, and electrical boxes are added into the wall. Something that may make these walls a little different than normal is the fact that everything is covered on the outside with Foil-faced Polyisocyanurate 1/2" which has an R value of 3.6. Also there are not a large number of windows, but rather larger windows. There is no fire-blocking or seismic reinforcement, plywood corner bracing is done with metal T reinforcement. Maybe using 25% will be good enough. that is what i willl use unless you suggest otherwise.

    Some other things that will be different than normal… 1.) There is a south facing 36’ long wall that has a 4’ x9’ of trapped air with another wall enclosing that area which is casement triple glazing starting 36’ from the floor up to the header, there are 5 posts framed between the windows. There is a brick wall for mass on the house side of that room, as well as a cement floor. This area is not heated except by the sun. The purpose of this room is only to provide solar gain heat. (More importantly a toy room for grandchildren they say!) My guess was to treat the interior wall of that room as though it has over 12” of trapped air then what ever the R factor would be for that mostly glass wall, but that does not account for the ceiling heat loss. I will leave that up to you to decide.

    2.) There is a glass enclosed porch on the east side of the house with a 22’ long wall that is much the same thing as the solar room but without the cement floor and brick mass wall. This area does have a vaulted ceiling

    I will begin to put these numbers together on the spreadsheet. I will come back to you when I have one area together to see if you agree with my information.
    Thanks for all of your help.

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    Here are my calculations for the second floor bedroom/ bathroom areas. I have included the closets and bath in each area, as well as the 10' hall. The 2nd area is two adjacent bedrooms and bath. This area is seldom heated with the baseboard except when below 10 outside, and that means zone below is running too. The heat loss from below provides most heat. There is nothing in this calculation for the stair that comes from below, but the stairs area is included in the square feet of this floor. I hope this table comes through in a legible format.

    MBR w bath & closet
    __________ U-factor _x_ area__x__design delta-T_=_heat loss
    U factor area delta T BTU/ HR
    Windows 0.38 49.5 71 1335.51 BTU/HR
    Doors 0 0
    Walls 0.0464738 397 71 1309.957012 BTU/HR
    Ceiling 0.016764459 379 71 451.1148365 BTU/HR
    skylight 0.38 4 71 107.92 BTU/HR
    ceiling fan 0.540540541 4 71 153.5135135 BTU/HR
    Room total: 3358.015362 [B]BTU/HR[/B
    ]Total Slant Fin= 12'


    Br 2 & 3 w bath & closets
    __________ U-factor _x_ area__x__design delta-T_=_heat loss
    U factor area delta T BTU/ HR
    Windows 0.38 27.8 71 750.044 BTU/HR
    Doors 0 0
    Walls 0.0464738 397 71 1309.957012 BTU/HR
    Ceiling 0.016764459 379 71 451.1148365 BTU/HR
    skylight 0.2331 4 71 66.2004 BTU/HR
    Room total: 2577.316248 BTU/HR
    Total Slant Fin= 10'


    BTU Loss for total upstairs: 5935.33161
    This area is one heat zone

    I have figured how to calculate the heat loss to the sun room and porch area. I know the minimum temperature in these rooms, just like the shop. So the Delta T in the shop is 25, the delta T to the sunroom is 35, and the delta T to the porch is 45. So I just use the regular wall construction U factor and us the different Delta T for these areas. Dah!
    Last edited by Heating in Colorado; 10-03-2013 at 11:12 AM. Reason: Changing last line

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    In the trades Dana's Avatar
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    Foil faced iso on the exterior is a standard construction these days- even enshrined in building codes. (In places where R20 is required for 2x construction R13 2x4 + R5 exterior foam is a code-accepted alternate.)

    When calculating the whole-wall R it's safe to calculate the assembly without the foam layer, then add it's R value at the end. But don't assume R3.6 is the right number to add: Polyiso drops with R value with falling temperature. Half-inch iso on the exterior will be no better than ~R3 at 0F for purposes of heat load analysis.

    With a 12" air gap between the glass and the brick wall, you can't count the air films in that trapped space, since it will have strong convection turbulence breaking them up. You can still count the air film on the conditioned space side, but not the exterior (it doesn't take much of a breeze to break it up on a residential sized wall assembly.)

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    When I built my first house in 1971, in 44720 Ohio, my mentor told me I was stuffing money down a rat hole by making the ceiling R19 instead of R13. He told me I would never recover the cost in the sale. He only built custom homes. We built side by side equal houses and he told me I would not recover one cent more if I did that. I also added additional outlets. He was right! He built and sold two and I had not sold my first one yet! Boy have things changed!

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    In the trades Dana's Avatar
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    DYA think? <LOL>

    Gas isn't 15 cents/therm any more and heating oil is WAY over 25 cents/gallon!

    Code min in MA right now is R38 attic, R13+5 (or R20) walls, R10-foam ( or R13 batt) on the foundation walls, and R10 foam sub-slab.

    When MA finally goes to IRC 2012 the attic-R min bumps up to R49, the walls stay the same as does the sub-slab R, but the foundation goes to R15 foam/R19 batt.

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    Dana

    Well, I am certainly glad to see that someone has figured that out since I began building.
    I have a couple questions on my heat loss calculations. In the basement area, I have not added in any loss to the floor above at this point. I understand that that does affect the heat loss for the room, but for the house. I have also done the same for the 1st floor loss to the second floor. There is nothing in the calculations for the stairs between the basement, 1st & 2nd floor. Is it okay to leave it that way? I understand that the total heat loss for each area below will be greater.

    In the basement only part of it is heated, the other part has the Heatmaker and that puts off enough heat to not see a great difference. Possibly a lower BTU more efficient furnace will require some added radiation area. So the loss between these areas is not considered.
    Some creature comfort comments: Remember that in the past 25 plus years, the basement has been kept warmer, than the 1st floor and the 2nd floor cooler yet. This allows the Zone 3 on the 2nd floor to only come on when it is pretty cold and other zones are normally running too. Just some thoughts as to hoe I have lived with the system. It is a tight house and I tend to be a very warm person, thi=us I prefer to sllep in the cooler 2nd floor area.

    In the shop area which is only heated on occasion for the common wall with the house, I will have a heat gain from the house, how is that figured? Do I take the loss from that wall and add it as a gain for the shop?

    I have not calculated the shop numbers yet.

    There is a stairs going from the basement to the shop in the shop area. The shop is far undersized in radiation, so that 4’ door from basement is opened to raise shop temperature faster when heat is needed, since the radiation in basement is so over sized.

    I currently have the following numbers in total for the area by each zone. All Slant Fin is Ύ” except in basement area where it is ½”. I can give you greater breakdown if you believe there is a problem.

    Basement finished area
    BTU Loss/ Hr = 422
    Slant fin = 14’

    Basement unfinished area
    BTU Loss/ Hr = 674
    Slant fin = 0’


    The above is Zone 1 Basement
    BTU Loss/ Hr = 1096
    Total Slant fin = 22’ (1/2”)


    Next Zone:

    Living Room & Entry
    BTU Loss/ Hr = 2484
    Slant fin = 13’

    DR & Kit
    BTU Loss/ Hr = 2601
    Slant fin = 19’

    Office
    BTU Loss/ Hr = 843
    Slant fin = 9’

    Entry & ½ ba
    BTU Loss/ Hr = 1570
    Slant fin = 5

    The above is Zone 2 1srtFloor
    BTU Loss/ Hr = 7497
    Total Slant fin = 46’


    Next Zone:

    MBR & bath
    BTU Loss/ Hr = 3314
    Slant fin = 12’


    BR2, BR3 & bath
    BTU Loss/ Hr = 2560
    Slant fin = 10’

    The above is Zone 3 2nd floor
    BTU Loss/ Hr = 5874
    Total Slant fin = 22

    Next Zone:

    Shop Zone #4 will go here when completed

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    Dana
    I have calculated the shop heat loss using this method. I used the common wall with the house as a heat gain the same as the loss from the house. I did not calculate any loss for the concrete floor which is on grade. Should that be added in as R of concrete with the delta to the earth?

    I used delta 41 since the heat is kept at 40 when not used. When the area is heated I do not use it if the outside temperature is below 20 and then only heat it to 60 thus making the delta T still 41. So as I see it, the Delta T is always 41 for design. Do you agree with this?


    The Slant fin in the shop is only 20', which is low when trying to raise the temperature 20 degrees for use.

    So if all of this is correct, that shows the total loss for the everything at design temperature of -1 as follows:

    House BTU loss
    Basement 1096
    1st Floor 7497
    2nd floor 5874
    Shop 2900
    TOTAL 17367


    Your thoughts? I can give you how anything is calculated as a cross check, os specifics of the construction.
    M

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    For our first-cut purposed the loss through the slab to the ground is pretty negligible- within the margin of error.

    So your zone totals are"

    Zone 1: 1096 BTU/hr, 14' of baseboard, or 78 BTU/ft-hr

    Zone 2: 7046 BTU/hr, 46' of baseboard, or 153 BTU/ft-hr

    Zone 3: 5874 BTU/hr, 22' of baseboard, or 267 BTU/ft-hr

    Total heat load (except shop): 14,016 BTU/hr <<-seems on the low side for a house with a lot of glass, but not super-low, given the 530 therms/year number.

    Adding a 25% fudge-factor for below-grade losses, ventilation & infiltration air etc and the whole house load is still looking like ~17,500 BTU/hr, which is a tiny load- a modulating condensing boiler would be a waste here: The whole house load is barely above the minimum-fire output of most mod-cons, and the load of even the highest loss zone (zone 2) is about half the output of the smallest in the line of most mod-cons. Worse yet, only Zone 2 has enough radiation to keep a mod-con boiler from short-cycling with 120F output temps (where it needs to be to break into the mid-90s for efficiency.)

    Adding in the 2900 BTU/hr (145 BTU/ft-hr on the fin-tube) of the shop you're still at only ~20 KBTU/hr. (And yes,the 41F as-used delta-T is the right way to run that calc.)

    Taking your worst-case load/ baseboard number (zone 3) and applying the same 25% "all of the rest" factor it's looking like (1.25 x 267=) 334BTU/foot of baseboard. Consulting a SlantFin output spec, that zone will need an average water temp (AWT) of about 140F on design day, the others could get by with 120F. Assuming a 20F delta-T on the zone-3 baseboard you would need 150F water.

    Even the whole-house load is too small to keep from short-cycling a 3-plate forced-draft mid-efficiency cast iron boiler.

    The fossil-burner approach to this that works would be a power drafted combi-hot water heater internal heat exchanger, but you'd be advised to add more radiation to Zone 3 to get it's load/length ratio more in line with zone 2, getting the max water temp down to the domestic hot water temperature range. The thermal mass of the water in the tank keeps the burner from short-cycling, and if you add enough radiation to Zone 3 to where it can heat the zone at 120F AWT you can just set the tank to 130F-140F and forget about it.

    For more money you could get condensing efficiency by going with a Vertex or Polaris hot water heater, but that would require a bit more system design work and the added expense of a bronze-impeller pump & heat exchanger.

    If there isn't sufficient free wall for baseboard on the Zone 3 to just add more baseboard (proportionally, about 1.6-1.7x what's currently there) to get the total length up to something like 35-40', you can still get there with small panel radiators, which have a greater comfort factor than fin tube, but are considerably pricier.

    It may not work out as well depending on the floor plan layout, but your heat load is within the 0F output of a 1.5 ton ductless mini-split/multi-split. A good 1.5 ton mini-split will have an operating cost comparable to heating with a power vented Combi-2 hot water heater, and would have the additional benefit of high-efficiency air conditioning. But since it's a point source (or multi-point source) heating system, the individual heat loads of doored-off bedrooms might need supplemental heat to keep the comfortable at 0F with the doors closed. In my neighborhood a good 1.5 ton single head unit runs ~$4-4.5K installed, but with a mostly DIY approach it's about half that. A 2- head 1.5-2 ton comes in around $5-5.5K. As currently zoned #2 and #3 have sufficient load to warrant an individual head, but if you leave all the doors open you'd be able to heat them with a single head, if the convective paths are reasonable. (You'd still have to figure out what to do for hot water too.)

    If it were my place I'd be inclined toward a Vertex or Polaris condensing hot water using the Taco X-Pump Block pre-engineered potable/heating isolation, and adding panel radiators to the bedroom zones, but that's a significant cost up-tick from a Combi-2 plus additional baseboard. The LAST thing you'd want do to is install an expensive mod-con boiler or low-mass combi heater and short-cycle it into an early grave. A tiny cast-iron Burnham ESC-3 power vented boiler and a bargain-basement electric hot water heater (not wired up) impressed into service as a buffer tank could work, but it takes a bit of design & tweaking to get right, and in the end would only be marginally more efficient than a Bradford White Combi-2.

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