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Thread: Advice on converting oil boiler to gas, adding indirect water heater

  1. #16
    In the trades Dana's Avatar
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    It never pays to be "conservative", always be aggressive heat load calculations, because the error creep is substantial, and oversizing creates more efficiency & comfort problems than being even 10% undersized.

    To start with, the 99% design temp for Philly is +15F, not +10F. At a 70F indoor temp, +10F outdoors that's a 60F delta-T. Right off the bat that's an 8% overshoot on sizing.

    For windows to come in with 21,756/555= 39BTU/ft-hr at a delta-T of 60F implies a U-factor of (39/60=) 0.65, which implies the crappiest possible 1970s clear glass double pane replacement windows with aluminum frames. A wood-sash double-hung with clear glass aluminum triple-track storms comes in at about U0.5, as to vinyl double pane replacement windows. Maybe you have the world's crummiest double pane windows, but if not and they're closer to U0.5, that 21,756 BTU/hr is really probably more like 16,750, a 4000BTU/hr overshoot at 60F delta, but if using the +15F outside design temp is about a 5K BTU/hr overshoot.

    To lose 10BTU/ft-hr for wall area at a 60F delta-T implies a U-factor of (10/60=) 0.17, which is a whole-wall R of (1/0.17=) R6, which implies almost no wall insulation whatsoever. A 2x4 wall with crappy fiberglass R11s or 1940s vintage rock-wool comes in at about U0.11 at a 25% framing fraction. Don't know what you've got, but if it's a timber framed wall with ANY cavity fill figure the U-factor is about 0.1, and that 27,050 BTU/hr is actually (.1/.17 x 27,050= ~16,000 BTU/hr, peeling 10K off the heat load.

    A ceiling losing (1920/1200=) 1.6 BTU/hr at a 60F delta-T is a U-factor of (1.6/60=) 0.027, which is (1/0.027=) R37 (a credible number!)

    Infiltration losses of 37,875/hr at 60F imply a leakage rate of [37,875/(60 x 0.018)= 35,069 cubic feet per hour, or 584 cfm, which is an INSANE amount of air leakage for a house that has glass in the windows, and doors that close. The simple models overestimate by about a factor of two unless the leakage points are true big round unimpeded holes. Leakage thorough cracks or fiber insulation has a heat-excanger effect, which lowers the conducted losses at those points. The air doesn't enter the conditioned space at the outdoor temp, nor does he exiting air leave the sheathing at the indoor temp. Assuming you don't have multiple open undampered flues, after air sealing, probably cut that that 38K number to something under 19K using the crudest possible model, and the real number is probably more like 12K, a reduction of 26K.

    A floor losing 6BTU/ft implies a very cold basement or vented crawlspace with no foundation insulation and little to no insulation between the joists, but OK let's just leave it

    Plug loads, and live humans will usually take at least 1000BTU/hr of the load.

    So starting with your 82K number...

    ... reducing by 4K for window adjustments leaves you at 78K...

    ...reducing by 10K for wall-insulation adjustments you're at 68K...

    ... reducing by 26K for infiltration adjustments gives you 42K...

    ... peeling off another 1K because it's an occupied house gives you 41KBTU/hr. Literally half what you estimated.

    Not perfect, but that's the likely order of magnitude. Upsize it by 25% if you like "just to be sure" and you're in the low 50s, which would still be a credible number (but a number that you can cost-effectively work on.)

    Most tight 2x4 homes with insulation and storm windows in my neighborhood come in at about 15 BTU/ft at 0F. (Where 0F is an almost rational design temp, though the 99% design temp here is +5F.) I live in a 2400' +1500' of semi conditioned basement (never drops below 65F in winter) 2x4 framed antique with only ~R20 in the roof and triple-tracks over antique double hungs with known gaps in the wall insulation, and my heat load at the +5F design temp is under 35KBTU/hr, at 0F it's still well under 40K. When I first moved in it was closer to 50K as measured by fuel use against heating degree days, but with air sealing the grossest leaks and adding wall insulation to ~85-90% of the wall areas (some parts need to be ripped open to retrofit properly) it brought the heat load down to about 40-42K, then with further air sealing and putting 3" of reclaimed roofing foam on the foundation & band-joist it's now a bit under 35K. I'm radiation-limited to about 43-44K at the fixed temperature I'm running the system, but this place has handled -5F and slightly lower outdoor temps without losing ground.

    Even at 40K for 2400' of fully-conditioned space is 17 BTU/ft, 35K for 2400' is 15 BTU/ft, but if you counted the 1500' of semi-conditioned basement thats under 10BTU/ft, and that's at +5F. With any reasonable weatherization you'd surely be between 10-15 BTU/ft @ +15F, or ~59K max. Sizing the boiler any larger than that would be a waste, and you'd probably never actually be cold with a 50K condensing boiler.

    If you have a mid to late winter oil bill with a K-factor stamped on it (or gallons between exact fill up dates and a zip code for looking up weather data) it's easy napkin-math to put an upper bound on the likely heat load- it's a good stake to put in the ground that has to be explained away if it differs much from what other heat load calculations come up with. (A 3 week vacation in FL with the thermostat turned down to 50F might be one such explanation, if it comes in well under the other calculations. :-) )

    82K for 3900' is 21 BTU/ft, which is a pretty rare condition at +10F for a home with double panes and at least some insulation.

  2. #17
    In the trades Dana's Avatar
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    Just saw your post indicating that it's "mostly brick". What is the wall stackup on the brick, and what U-factor did you use?

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    DIY Member jefferson17's Avatar
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    Again - I really can't thank you enough for your time, patience and expertise! Truly I'm blown away at your most gracious sharing of your time. WOW! You really know your stuff. Ok - I'll try and fill-in the gaps, so that you may make more specific recommendations.

    Please bear in mind that most of the house is Victorian - essentially a rectangle twin - 1875 brick/masonry construction. We did a great job on the attic above the 4th floor but there is still a lot of original window and wall upstairs.

    Only the rear addition was built with wood construction. We are less concerned with the addition since we did so much spray foam on it - and it is heated/cooled by the Fujitsu dual heat pumps.

    Quote Originally Posted by Dana View Post
    It never pays to be "conservative", always be aggressive heat load calculations, because the error creep is substantial, and oversizing creates more efficiency & comfort problems than being even 10% undersized.

    To start with, the 99% design temp for Philly is +15F, not +10F. At a 70F indoor temp, +10F outdoors that's a 60F delta-T. Right off the bat that's an 8% overshoot on sizing.

    >> For windows to come in with 21,756/555= 39BTU/ft-hr at a delta-T of 60F implies a U-factor of (39/60=) 0.65, which implies the crappiest possible 1970s clear glass double pane replacement windows with aluminum frames. A wood-sash double-hung with clear glass aluminum triple-track storms comes in at about U0.5, as to vinyl double pane replacement windows. Maybe you have the world's crummiest double pane windows, but if not and they're closer to U0.5, that 21,756 BTU/hr is really probably more like 16,750, a 4000BTU/hr overshoot at 60F delta, but if using the +15F outside design temp is about a 5K BTU/hr overshoot.
    Most of the windows are original victorian - 23 windows in total in a 4 floor section. Most of these windows are pretty big - often 3' wide by 5' high. Perhaps 35 are even 5.5' high. Single pane with wood sashes. Nearly all of them have storm windows but they are metal frame single pane and probably leak a fair bit of air around the edges. I'm not even sure if they are better than nothing at all.

    The addition on the back is a mixed bag for the windows. 5 double pane aluminum frame sliders, a few single pane wood windows - one without a storm (storm track was all messed-up). 2 high efficiency Okna windows that we put in. Some large picture windows - with a whole bunch of small sections - but they are older double pane, wood frame. We did a LOT of spray foam insulating this past spring in that section and that is heated/cooled only using the Fujitsu heat pumps (or whatever heat happens to make it's way back there).


    >> To lose 10BTU/ft-hr for wall area at a 60F delta-T implies a U-factor of (10/60=) 0.17, which is a whole-wall R of (1/0.17=) R6, which implies almost no wall insulation whatsoever. A 2x4 wall with crappy fiberglass R11s or 1940s vintage rock-wool comes in at about U0.11 at a 25% framing fraction. Don't know what you've got, but if it's a timber framed wall with ANY cavity fill figure the U-factor is about 0.1, and that 27,050 BTU/hr is actually (.1/.17 x 27,050= ~16,000 BTU/hr, peeling 10K off the heat load.

    House built in 1875 so some walls lack any insulation. The entire original section is all brick and masonry. Some of it is very thick - basement is below ground. 1st floor is mostly below ground and also shares 1 wall with the adjoining twin.

    Upstairs apartments (2 floors, some 1100 square feet) are strictly just brick then lath and plaster. For the 2nd floor (street level - our dining room and new kitchen), we spray foamed the walls before putting up 5/8 sheetrock. It's only a .5-1" layer - which is all that would fit but should provide a good bit of air sealing for that area (500 Sq feet).


    >> A ceiling losing (1920/1200=) 1.6 BTU/hr at a 60F delta-T is a U-factor of (1.6/60=) 0.027, which is (1/0.027=) R37 (a credible number!)

    We air sealed all penetrations to the attic w/ fire-rated foam, then filled the attic as high as possible with blown fiberglass (mansard roof construction - just a low pitched attic area - highest point is perhaps 4'). In the middle the insulation is quite thick and much less so at the edges - but still probably 8-10". We also did have them put in a wind-powered fan up there, and they installed baffles to allow the soffits to breathe (yeah I know they aren't supposed to in this type of roof - but they have so many cracks that they might as well be modern from that viewpoint).

    >> Infiltration losses of 37,875/hr at 60F imply a leakage rate of [37,875/(60 x 0.018)= 35,069 cubic feet per hour, or 584 cfm, which is an INSANE amount of air leakage for a house that has glass in the windows, and doors that close. The simple models overestimate by about a factor of two unless the leakage points are true big round unimpeded holes. Leakage thorough cracks or fiber insulation has a heat-excanger effect, which lowers the conducted losses at those points. The air doesn't enter the conditioned space at the outdoor temp, nor does he exiting air leave the sheathing at the indoor temp. Assuming you don't have multiple open undampered flues, after air sealing, probably cut that that 38K number to something under 19K using the crudest possible model, and the real number is probably more like 12K, a reduction of 26K.

    Hmmm! Maybe we should have a follow-up Blower Test? We had one done about 18 months ago with an energy audit - before we started all that attic insulating and followed-up with spray foam. At that time, our place was very leaky. We are very confident that it is much improved. This summer was MUCH more comfortable.

    Maybe we would benefit from a proper heat loss analysis, now that we have changed so much. The 75K btu figure I came up with made me nervous. It just seemed so LOW, you know? So I changed the design day from 15 to 10 F.


    >> A floor losing 6BTU/ft implies a very cold basement or vented crawlspace with no foundation insulation and little to no insulation between the joists, but OK let's just leave it

    Hmmm well much of the basement is entirely below grade. The original victorian part is about 18x40, with 18-24" thick masonry walls, coated in some kind of plaster. The floor is concrete. The 400 square foot addition basement in the rear is all block construction. There isn't any insulation on the walls or floor anywhere. I'm planning to install pieces of 2" foam board up between the joists around the perimeter - especially in the addition area, where it's more leaky, and it's exposed on 3 sides. The original basement area is only exposed on 1 side and even then not much of that.

    A FEW of the heating pipes down there have aspestous wrapping (and we leave that alone). We could wrap all the other pipes but if we do that we'll have a cold basement right under the 1st floor living area - so our thinking is let it stay at about 68-70 (big heating pipes but no radiators), and it'll help keep the floor above the basement (1st floor) warmer. That's my thinking, anyway.


    Quote Originally Posted by Dana View Post
    Plug loads, and live humans will usually take at least 1000BTU/hr of the load.

    So starting with your 82K number...

    ... reducing by 4K for window adjustments leaves you at 78K...
    ...reducing by 10K for wall-insulation adjustments you're at 68K...
    ... reducing by 26K for infiltration adjustments gives you 42K...
    ... peeling off another 1K because it's an occupied house gives you 41KBTU/hr. Literally half what you estimated.

    Not perfect, but that's the likely order of magnitude. Upsize it by 25% if you like "just to be sure" and you're in the low 50s, which would still be a credible number (but a number that you can cost-effectively work on.)
    Given all the additional info ... would you still stand by these or am I perhaps more like 60, 65,70K?


    Most tight 2x4 homes with insulation and storm windows in my neighborhood come in at about 15 BTU/ft at 0F. (Where 0F is an almost rational design temp, though the 99% design temp here is +5F.) I live in a 2400' +1500' of semi conditioned basement (never drops below 65F in winter) 2x4 framed antique with only ~R20 in the roof and triple-tracks over antique double hungs with known gaps in the wall insulation, and my heat load at the +5F design temp is under 35KBTU/hr, at 0F it's still well under 40K. When I first moved in it was closer to 50K as measured by fuel use against heating degree days, but with air sealing the grossest leaks and adding wall insulation to ~85-90% of the wall areas (some parts need to be ripped open to retrofit properly) it brought the heat load down to about 40-42K, then with further air sealing and putting 3" of reclaimed roofing foam on the foundation & band-joist it's now a bit under 35K. I'm radiation-limited to about 43-44K at the fixed temperature I'm running the system, but this place has handled -5F and slightly lower outdoor temps without losing ground.

    Even at 40K for 2400' of fully-conditioned space is 17 BTU/ft, 35K for 2400' is 15 BTU/ft, but if you counted the 1500' of semi-conditioned basement thats under 10BTU/ft, and that's at +5F. With any reasonable weatherization you'd surely be between 10-15 BTU/ft @ +15F, or ~59K max. Sizing the boiler any larger than that would be a waste, and you'd probably never actually be cold with a 50K condensing boiler.

    If you have a mid to late winter oil bill with a K-factor stamped on it (or gallons between exact fill up dates and a zip code for looking up weather data) it's easy napkin-math to put an upper bound on the likely heat load- it's a good stake to put in the ground that has to be explained away if it differs much from what other heat load calculations come up with. (A 3 week vacation in FL with the thermostat turned down to 50F might be one such explanation, if it comes in well under the other calculations. :-) )

    82K for 3900' is 21 BTU/ft, which is a pretty rare condition at +10F for a home with double panes and at least some insulation.[/QUOTE]


    Will this help? On a really cold month we can blow through 200 gallons of oil in 3.5 to 4 weeks. But we didn't air seal and re-insulate the attic until this past March. And didn't add spray foam on 2nd floor walls and rear addition until this past May.

    When I buy oil I just fill it up, via COD. There is no "K-factor", whatever that is. I just fill the darn thing and hand over a bunch of cash. Usually about $600-700.

    Thanks!

    Jeff
    Last edited by jefferson17; 09-25-2013 at 12:36 PM. Reason: getting instant email notifications

  4. #19
    In the trades Dana's Avatar
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    I'd have to run the real numbers on the real construction to come up with a sort of real heat load number. The type of brick matters when it's 18-24" thick- something difficult assign a U-factor to, or even a range, but it's probably at least R5 (U0.20) from a thermal mass dynamic modeling point of view, and could be much higher. I assume this is a town house, and the other side of the common wall with the "twin" is a heated space (U-factor = 0.)

    But a couple of comments:

    Any single pane windows with leaky or absent storm windows can cost-effectively be upgraded with tight-fitting low-E storm windows. Even though they are more expensive than clear glass windows, the payback is 5 years, not 10 due to the higher performance. The as-is clear glass storms+ single panes have a U-factor in the U0.5-U0.6 range. Tight low-E storms over those antiques would deliver U0.31-U0.34. Harvey makes the tightest storm windows in the biz, and have a low-E glazing option. The Larson low-E storms sold through the box store chains don't suck if you spring for at least the "Silver" version (the low end "Bronze" series leak a lot more air.)

    In the basement it's far better to put the foam on the exterior foundation walls that to cut'n'cobble between joists. This is for several reasons: Putting it on the foundation walls brings the joist edges and boiler completely inside the conditoned space, which means the wood stays warmer (= drier), and the standby losses of the boiler accrue to the conditioned space. Furthermore, it's damned near impossible (even with copioius amounts of spray foam) to really air seal at the basement-ceiling, but fairly straightforward at the foundation wall.

    Unless you're using fire-rated Thermax you'll be required to put in a thermal barrier like half-inch gypsum over any wall -foam. An inch of foil faced iso and a 2x4 studwall with unfaced R13s might be cheaper, and would deliver ~R16 whole-wall (U0.06) after factoring in the thermal bridging of the studs. Keep the bottom edge of any polyiso off the slab, as well as the bottom plate of the studwall by putting it on an inch of EPS as a thermal & capillary break. (Polyiso can wick ground moisture, as does wood. EPS won't.)

    200 gallons on 3.5-4 weeks of "...really cold month..." isn't enough to go by, unless you have the EXACT fill up dates and a complete fill-up volume, so we can look up the heating degree-days for your zip code. But let's play the game anyway. The binned hourly mean temp for January in Bristol is ~32F according to weatherspark.com data, so lets assume a really cold month averages about 30F. That means that your heating degree day averaged (base 65F) 65F-30F= 35 HDD/day. You're burning something like 200gallons/25 days or 4 gallons per day.

    In an 85% burner that 4 gallons is delivering 0.85 x 4 gal x 138,000 BTU/gal= 469,200 BTU per day, or an average of 469,200 BTU/24= 19,550 BTU/hr at 35F below the presumed 65F heating/cooling balance point (it'll be close enough).

    That's 19,550/35F= 559 BTU per hour per heating-degree.

    At an outside design temp of +15F you have 65F-15F= 50 heating degrees, and a heat load of 50F x 559= 27,950 BTU/hr

    At an outside design temp of +10F it's 55 heating-degrees, and an implied heat load of 30,745 BTU/hr.

    In order for the heat load to be 2x that would have requires an average outdoor temp below 0F, which clearly didn't happen, or you were really looking at 2-weeks of oil use, not 3.5-4 weeks. No matter what your heat load for the zones heated by oil is probably under 50K, and is likely under 35K, and may even be under 30K. The smallest of the line ~50-60K mod-cons or or semi-smart 3-plate cast iron boilers are probably your best bet. But see if you can't nail down some exact dates & volumes on the oil fill-ups base on the real hdd for those dates at a weather station near you. In gross terms, if you're using "only" 700-800 gallons/year or even 1000 gallons/year your heat load at +15F simply can't be 75K or anything close to that:

    An average year in Philly sees fewer than 5000 HDD. At 1000 gallons and 5000 HDD that would be 0.2 gallons/HDD which is about 980 BTU/degree-hour. 980 BTU/degree-hour x 50 heating-degrees is 49,000BTU/hr, the +15F heat load. 980 BTU/degree-hour x 55 heating-degrees is 54,000BTU/hr, the +10F heat load.

    Are you still thinking 75K is "low" heat load number?

    If you can, add up the total fuel use in the past year. If it's under 800 gallons, any 50K boiler (condensing or otherwise) will cover your actual loads, assuming you didn't spend January in Belize with the thermostat turned down to 45F.

  5. #20
    In the trades Dana's Avatar
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    OK, now that I've had my PM coffee I'm allowed to do math in my head, unlike when I wrote: "...200 gallons/25 days or 4 gallons per day."

    Uh... make that 8 gallons/day not 4. (DOH! )

    Which makes the +15F heat load number 55,900 BTU/hr...

    ...and the +10F number 61,490 BTU/hr.

    That's still 3-plate Burnham ESC3 (60K DOE output) territory, but I'd want better fuel use data before saying for sure. If you insulate the foundation (and not the basement ceiling) you'll likely have margin with the ESC3.

    Don't bump up to the ESC4 (90K DOE output) "just to be sure" rather, instead BE DEAD-SURE that the ESC3 won't actually cut it after a more careful analysis. If running a heat load calc on the construction's U-factors, run it on the "after" picture. The uninsulated foundation is likely to be on the order of 10K of load, a load that drops to 1K or less after insulating.

    So if fuel use analysis is telling you it was ~60K in a less-insulated condition, it'll be ~50K after just insulating the foundation walls & band joist, which is worth doing on a number of grounds other than mere heat load reduction.

    If you punted and went with the ESC4 and your post-insulation heat load turns out to actually be under 45K (a realistic possibility), you'd be more than 2x oversized, the condition you're trying to get away from. (AFUE testing is done at 1.7x oversizing for the load, which is the maximum you'd ever want to be.)
    Last edited by Dana; 09-25-2013 at 01:57 PM.

  6. #21
    DIY Member jefferson17's Avatar
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    Added: fyi on hot water needs. We have 4 showers. There is 1 bathtub upstairs (4th floor apt) but is used only for showers. Each upstairs apt has 1 shower. We have 2 showers in our unit (floors 1 and 2). It's just Amy and I in our unit. All shower heads (including ours) are Delta h20 kinetic - using 1.85 gpm.

    >> I'd have to run the real numbers on the real construction to come up with a sort of real heat load number. The type of brick matters when it's 18-24" thick- something difficult assign a U-factor to, or even a range, but it's probably at least R5 (U0.20) from a thermal mass dynamic modeling point of view, and could be much higher. I assume this is a town house, and the other side of the common wall with the "twin" is a heated space (U-factor = 0.)

    It's a victorian twin, not townhouse. So one wall is shared with the adjoining structure (except rear addition, which is open on 3 sides). The upper 3 floors are brick and about 8" thick. But that brick is pretty leaky, for sure. The lowest living floor has MUCH more thick masonry - about 18", sometimes closer to 24" We've had to drill through it so we really do know.

    >> Any single pane windows with leaky or absent storm windows can cost-effectively be upgraded with tight-fitting low-E storm windows. Even though they are more expensive than clear glass windows, the payback is 5 years, not 10 due to the higher performance. The as-is clear glass storms+ single panes have a U-factor in the U0.5-U0.6 range. Tight low-E storms over those antiques would deliver U0.31-U0.34. Harvey makes the tightest storm windows in the biz, and have a low-E glazing option. The Larson low-E storms sold through the box store chains don't suck if you spring for at least the "Silver" version (the low end "Bronze" series leak a lot more air.)

    Unfortunately, it's just not a good option for us. Replacement windows get quite expensive for our larger sizes. I've shopped around. Our house is also historical so more PITA. The payback would be at least 10 years - probably more like 15. Even more if we went with wood not vinyl. The money we spent on air sealing and insulation was well worth it though.

    >> In the basement it's far better to put the foam on the exterior foundation walls that to cut'n'cobble between joists. This is for several reasons: Putting it on the foundation walls brings the joist edges and boiler completely inside the conditoned space, which means the wood stays warmer (= drier), and the standby losses of the boiler accrue to the conditioned space. Furthermore, it's damned near impossible (even with copioius amounts of spray foam) to really air seal at the basement-ceiling, but fairly straightforward at the foundation wall.

    >> Unless you're using fire-rated Thermax you'll be required to put in a thermal barrier like half-inch gypsum over any wall -foam. An inch of foil faced iso and a 2x4 studwall with unfaced R13s might be cheaper, and would deliver ~R16 whole-wall (U0.06) after factoring in the thermal bridging of the studs. Keep the bottom edge of any polyiso off the slab, as well as the bottom plate of the studwall by putting it on an inch of EPS as a thermal & capillary break. (Polyiso can wick ground moisture, as does wood. EPS won't.)

    Outside isn't an option but I appreciate the info. Hmmmm ... ok so maybe not worth doing right now. I thought I could just use double-foil 2" foam boards (I've got leftover of this stuff), but I guess it's not an option without installing a bunch of drywall too (PITA right now). We can get around to that when we get more drywall done in our rear addition next year.


    >> 200 gallons on 3.5-4 weeks of "...really cold month..." isn't enough to go by, unless you have the EXACT fill up dates and a complete fill-up volume, so we can look up the heating degree-days for your zip code. But let's play the game anyway. The binned hourly mean temp for January in Bristol is ~32F according to weatherspark.com data, so lets assume a really cold month averages about 30F. That means that your heating degree day averaged (base 65F) 65F-30F= 35 HDD/day. You're burning something like 200gallons/25 days or 4 gallons per day.

    I assure you that we burned about 6.5 gallons per day (averaged) for the 3 coldest months last year. We filled up some 200 gallons for 3 months straight and the interval was always 3.5-4 weeks. We certainly used about 1000 gallons last year, perhaps a bit more. That boiler is just a monster.

    Of course - all of that is BEFORE we sealed the attic penetrations and filled it with as much blown fiberglass as would fit and before spray foam in rear addition (heat pump area), etc.

    >> Are you still thinking 75K is "low" heat load number?

    Ok ok - I'm believing you! LOL. So maybe 75K is high ... but after reading everything from you, it seems like 60-65K is at least pretty close and not "overly high". I'm going to look into getting a professional heat loss calculation done. That would be a worthy use of $100 I think.


    >> If you can, add up the total fuel use in the past year. If it's under 800 gallons, any 50K boiler (condensing or otherwise) will cover your actual loads, assuming you didn't spend January in Belize with the thermostat turned down to 45F.

    We definitely have used 1000-1200 gallons per year. But ... we also didn't add air sealing and insulation in the attic until march 2013 and spray foam in rear addition until may 2013.

    Gosh I WISH we spent Jan in Belize . We have 2 apts upstairs, so even if we WERE away we'd still need to keep the thermostats set to 68-70. They are fully programmable, and I've got them set for wake, away, back and night - with separate settings for sat and sun. We need to keep us (and the tenants) comfortable. All thermostats are in our areas on the 1st and 2nd floors. The tenants can't change anything (but they can open windows if they get too warm in the winter).


    Do you have any opinions on any specific high eff mod/cons? Here's one Buderus example, for discussions sake: http://www.pexsupply.com/Buderus-GB1...-Nat-Gas-or-LP.

    I'm just thinking ... if 90% mod/con is $3300 and a Burnham ESC4 (78K) is $2264 that HOW MUCH GAS in $ would 90% "high efficiency" really save us vs an 84% ESC or similar? My wild guess is maybe $100 per year? So that's 10 years for an ROI. If the mod/con needs ANY professional yearly touch - that would be wiped out and why even consider it? Any thoughts?

    Thanks!

    Jeff
    Last edited by jefferson17; 09-25-2013 at 05:46 PM. Reason: adding info on water use

  7. #22
    In the trades Dana's Avatar
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    I'm not talking about replacement windows, but rather single pane low-E storm windows, with a indium tin-oxide hard-coat low-E coating on the inner surface. The difference between code-min replacment windows and low-I storms on installed-cost is huge, but a tight low-E storm and an antique wood double hung can sometimes outperform a code-min replacement window, whereas clear-glass storms can't.

    You can still use double-foil on the interior side of the basement you can still get there by strapping them to the wall with 1x furring through screwed to the foundation with 3.5" TapCons 24" o.c. and mount half-inch wallboard to the gypsum on the furring. (This is how I insulated the foundation on my 1920s bungalow. In my case I used reclaimed 3" fiber faced 2lb roofing iso at about R18.) With 2" 1.5lb density foil faced you'd be at about R13, which is fine. Just keep the cut edge off the floor to avoid ground moisture wicking. You don't have to paint or fully finish the wallboard if you don't want to- its sole function is to provide a code-approved thermal barrier for the foam. As a DIY using your leftovers or reclaimed foam from de-construction vendors its VERY cost effective, and improves both the thermal & moisture conditoins in the basement by quite a bit. Use a thin shot of spray foam seal & insulate the foundation sill & band joist to the wall-foam, and fatten up the R with batts on the band joist. (You can use the same cut-up foam board on the band joist if you like, just seal it with can-foam at the seams.)

    We'd need to know the average daily temperature for that 6.5 gallons/day usage to turn that into a heat load number. If you plug in 1200 gallons in to the FSA calculator using Philly as the location and 1200 gallons/year usage, even with a highest-efficiency 105KBTU/hr 88% AFUE heat purge boiler it's coming up with about ~57K for a heat load @ +10F.

    If I plug in 1000 gallons/year it comes up with ~47K @ +10F with the highest-efficiency boiler.

    Using the model for the 83.7% AFUE + typical indirect with 150KBTU/hr of output (more similar to your setup, but probably still more efficient) at 1200gallons/year it's coming up with a heat load of 50KBTU/hr @ +10F, and at 1000 gallons/year it's 39,400 BTU/hr @ +10F.

    Your current boiler is nowhere as efficient as the heat-purged boiler less than half the size, and the odds of it being more efficient than the 150K boiler with the indirect are between slim & none which means your real heat load is under the 60KBTU/hr DOE output of the ESC3 , and about half the DOE 90K output the ESC4. The FSA calculator models for the boilers are based on real test data on real boilers, but the heating degree-day data are for the 25 year average season, not last season's data, so if last year was milder than the 25 year average there is a bias toward undersizing. But it would have to have been the warmest winter of the past century for your heat load to actually be 60K, perfectly matching the output of the 3-plater. It' highly unlikely that your heat load was higher as 55K even in the less-sealed less insulated state it was in, and after improvements already under way it is likely to come in quite a bit under 50K.

    With the boiler installed in the basement it is rightly sized in this type of installation by it's DOE output, not the I=B=R output. Only if the boiler is out in garage or otherwise outside the thermal envelope of the house would the I=B=R numbers be relevant. (That's one of the many reasons why you want to insulate the basement walls, not the floor, if the boiler is in the basement.) The ESC3's DOE output is 60,000 BTU/hr, and the ESC4's is 90,000 BTU/hr. With your heat load eventually settling below 50K (it's really already there), the ESC3 is by far the better choice in that product line.

    The efficiency you can get out of mod-con is a function of how much radiator you have, which determines the return water temp. The lower the average water temp, the higher your combustion efficiency. The AFUE testing is done with 120F return water, and I suspect you have sufficient radiation that most of the time you would have lower return water temps than that (if you dial in the outdoor reset curve), which means you would beat the published AFUE. Buderus makes nice boilers, and the minimum-fire of the GB142 (which tests at 95% efficiency in an AFUE test, not 90% BTW) is about half your design condition load, which means with the system and reset curves dialed in you'd be getting BETTER than 95% efficiency, compared to 85% with the 3- plate Burnham ESC. So after further building upgrades if you would be using 1200 therms with the ESC, you'd be using less than (1200 x 85%/95% =) 1074 therms with the mod con, probably more like 1050 therms, a savings of 150 therms/year. At a buck a therm it takes awhile to make up the difference in installed cost, but gas prices are currently at historical lows- they simply can't go lower and still support the production cost of getting the gas out of tight-shale reserves. (It takes an order of magnitued more drilling to get gas out of shale or coal than from traditional basin formation gas.) The price may stay reasonably stable near current pricing, but I'd expect them to rise over the lifecycle of the boiler. Designing & setting up a mod-con is more complicated than with simple cast iron too- not a DIY project by any means (unless you can convince the manufacturer to let you enroll in their installer training.) The difference in installed cost is guaranteed to be more than the sticker price of the boiler itself.

    At your heat loads the Triangle Tube Prestige Solo-60 or the Peerless PF-50 might be more appropriate, since their minimum-modulation is considerably lower, which means it will run in a modulating mode MOST of the time rather than just half the time with the GB142. But installer competence and local distributor support are more important than the which boiler vendor with mod-cons. Mod cons with aluminum heat exchangers are more sensitive to the system's water chemistry than those with stainless or cupro-nickel.

    If you're doing this DIY, go with the 3-plate cast-iron. Even though the ESC series tolerates 110F return water, with your high mass probably-oversized radiation you'd likely be seeing temps below that during periods of low load, so it's worth plumbing in a radiation-bypass loop with a ball-valve to be able to tweak the return water temps so that it's up to at least 110F by the time it's 5 minutes into a cold-start of the system.

    A flow of 4x 1.85gpm at a 65F mid-winter temperature rise is 240,000 BTU/hr, which your beastie boiler can pretty much handle. But with any boiler reasonably sized for your space heating load you'll absolutely need an indirect tank, and a fairly big one. For showering performance you can buy a lot of capacity with a drainwater heat exchanger downstream of the shower drain, feeding both the cold feed to the water heater AND the cold feed to the shower, but with multilple showers it's usually easier to let it feed the cold distribution for the whole house. At eastern PA incoming water temps the output of the DWHX will never exceed room temp by more than a few degrees, so it's not a real issue for other cold-water users during showers. At 2.5gpm a 3" x 60" or 4" x 48" returns more than 50% of the heat from the drain back into the system, roughly doubling the apparent capacity (and apparent efficiency) of the water heater in a shower type draw where the drain & hot water are flowing simultaneously It does nothing for tub-fill efficiencies though. If you really think you'll ever be running 4 showers simultaneously this technology would reduce the size of the indirect required from the 100-120 gallons to something in the 60-70 gallon range. From an energy savings point of view it takes awhile to pay off at a buck a therm, but being able to down-size the indirect it's a net savings up front, as WELL as the energy savings.


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