Heat loss calculation

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Old 10-31-09, 10:26 AM
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Heat loss calculation

Trying to do my own heat loss on my house and its a little confusing. I bought Siggy's book Modern Hydronics and used the calc on the cd that came with the book. I came up with around 27k btu on the 3 floors of my house not counting the basement. In an effort to get more options in the calculations i downloaded his Heat Load Pro software and am at over 30k btu just on the 1st floor.
Not sure if I'm doing it all wrong or what but I wouldnt expect that much of a diff. any suggestions you uys can ive me to make sure my results are accurate when i do this.
Also if the basement isnt going to be heated how much does that factor into the overall heatloss of the house vs. sizing the boiler since it wont have the demand of heating that area directly?
 
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Old 10-31-09, 01:03 PM
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Hi dings, direct or indirect, heat flows out of your basement like an open door. An 8" concrete wall has the same insulating ability as a single thickness of glass. Fortunately, much of the foundation is below grade and only counts a little.

I'm not familiar with with that program, but it does sound like something is off in either your first or second attempt. Trying to do one floor at a time might not be a good approach, as the ceiling above the first floor looses most of it's heat to the benefit of the second floor.

Tell us what you are entering for data, r-values, wall areas, and such and we will see if we can spot a problem. This is an important issue, you bought a program that should handle the calcs, so let's get you comfortable with using it.

I'll stop back,
Bud
 
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Old 10-31-09, 01:47 PM
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Remember that you only enter walls, ceilings, and floors that have unconditioned space on the other side. I made that mistake when I first did mine.
 
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Old 10-31-09, 02:43 PM
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27K BTU on 3 floors not including the basement seems almost impossible to believe in an area like Connecticut. Almost certainly the 1st attempt is wrong unless you have a SUPER air tight and insulated home.

I used the hvac-calc.com "manual-j" calculator and it was pretty easy to use after about 5 minutes of messing around with it. It was a bit pricey ($49 for the residential 3 month version) but was highly recommended by most hvac professionals from the information I found on it. Most said it was within +/- 2% of an actual long form manual-j.

As for helping you, as bud9501 said we would need a LOT more info to see where your mistakes - if any were made - are
 
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Old 10-31-09, 04:05 PM
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Most said it was within +/- 2% of an actual long form manual-j.
Which by the way also produces an estimate that may be in the neighborhood of 20-25% 'over'... So, in any case, don't take the number from either a manual manual-j, OR a software manual-J, and 'pad' it "just in case", because the padding is already built in.

Are you sure the 27K you got on the first run wasn't for just the first floor? in other words, is there something you have to 'click' to see the TOTAL? or did it actually say it was the total for the entire home? I find that hard to believe also.

How many square feet total is the home?
 
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Old 10-31-09, 05:50 PM
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That's why I think heat loss should be left to the professionals. There are many done and many done properly by homeowners. I have also seen many done wrong and oversizing or undersizing the equipment. Try the contractors in the area and see if they will do it. If so use them for the install. When I worked for the oil company we always did heat losses but did not reveal the results unless the homeowner bought the equipment from us. Did not like unpaid consulting.
 
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Old 10-31-09, 05:58 PM
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The first run was using the software that came with the modern hydronics book. I did it room by room. the version that comes with the book can only do 3 rooms at a time so i basically did each room then added them all up. I think the error came when I entered the r value of the walls. I am doing spray foam in 2x4 walls so i entered an r value of 21. I think it really wanted the effective r value. With the Heat load pro i can input all the materials in the wall. with 1/2" sheet rock, 3.5in of foam, the exterior sheathing, and the vinyl siding it gives me an effective r value of 10.6 (f hr sqft/btu). I was using .4 for the number of air changes an hr for the air leak %
The house is 2500 sq ft not counting the basement which is just over 1000sq ft.
I thought doing room by room was the proper way. am i better off to first do it with the total sq ft of the exterior walls and ceilings/roof and then do room by room so i can calculate the proper heat load for each space
 
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Old 10-31-09, 06:08 PM
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Originally Posted by rbeck View Post
That's why I think heat loss should be left to the professionals. There are many done and many done properly by homeowners. I have also seen many done wrong and oversizing or undersizing the equipment. Try the contractors in the area and see if they will do it. If so use them for the install. When I worked for the oil company we always did heat losses but did not reveal the results unless the homeowner bought the equipment from us. Did not like unpaid consulting.
I am completely redoing a 200 year old home. all the work is being done by myself. I had a contractor who is a friend of my fathers take a look at the place and he had his supplier come out and do a heat loss( the supplier only does it for contractors, they wouldnt come out when I called them). I was going to purchase everything from them but the pricing on just the boiler was $2k more than I found it for online. I dont mind payin a markup but that seemed a little crazy to me. since then I found another local supplier that will sell to me direct and his price on the same unit was $1800 less than the first guy. But I wanted to take a crack at doing the heat loss myself. the first guys told me I needed a 105kbtu boiler. I'm sure they did the heat loss properly but again I wanted to give it a shot and learn something in the process.
BTW I did offer to pay for the heat loss after I declined their services because I dont expect anyone to spend their valuable time for nothing
 
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Old 10-31-09, 06:41 PM
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Learning the details of a heat loss calculation goes hand in hand with improving the energy efficiency of your home. It tells you what is important and let's you play with various options.

Now, if a program is asking for the r-value the insulation in a wall, that's what they want. The program can adjust for framing. It should be explained in the instructions. When the guidelines for homes state R-21 for walls and R-49, they are talking about the cavity insulation, not the effective R-value.

Let's back up for a moment. How extensive will this renovation? Right down to the frame, or just inside, new windows or what. For example, spray foam isn't cheap and most people will opt for another approach when they see the price. You wouldn't want to do a heat loss and then change the plans. If you are replacing siding or drywall and new electric, there is the option of adding some layers of rigid inside or outside, which adds insulation, but also reduces the thermal bridging caused by the framing.

Share what you want for your plans and we will go from there.

Bud
 
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Old 10-31-09, 10:09 PM
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this is a total gut right down to the bare studs. Most of the windows were replaced before i bought it. I will be replacing the rest. I am not doing the outside yet so the siding is going to stay on.
I realize spray foam is not cheap. I had researched it some before deciding I wanted to use it.
heres a link to picture of the project
New House pictures by paintbyding - Photobucket
 
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Old 10-31-09, 11:03 PM
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Yeah, I'd call that a total gut rehab! I'm gonna have nightmares now... termites, carpenter ants, and powderpost beetles...
Not nearly as old a building, but, been there! I trust you know about "Timbor" ?

My guesstimate is right around 45-50K... if that.

Gonna be schweet when it's all done!
 
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Old 11-01-09, 02:35 AM
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Just a very rough estimate, very rough. 3.5" walls from foundation to attic, not including the ceiling, $12,000. You can probably have it done for the same as buying the DIY kits, just have to have everything ready for them which is often a problem. The other issue is spraying foam in the winter, it doesn't like the cold and the coverage goes down. Real cold and you can't spray. Plus, you have to have everything done before the foam, because there is not going back. Steps like electrical inspections are difficult to obtain on a room by room basis, plumbing as well and all will want to see the work before the foam. Have you looked at "flash and batt"? Also take a look at "Roxul" insulation. Bud
 
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Old 11-01-09, 06:43 AM
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ya. its fun fun fun.. bought it in may and really started working on it in august. NJ actually i didnt know about Timbor, but thanks. I had an exterminator come out and he said the powder post bettles were not around anymore. he didnt find any active holes. I'm keeping an eye out though.
My brother-in-law does spray foam in NY and will do the place for me at cost. I am still researching DYI options as I may need to do a few rooms at a time. Depends on when my current house sells. Room by room inspections are no problem. already spoke to the building inspector. I have considered flash and batt. does that still make it a "hot roof" doing the ceilings that way. I googled Rolux but didnt find anything on it.
 
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Old 11-01-09, 07:16 AM
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Roxul Inc.

What does your brother-in-law charge for closed cell foam? I'm interested in doing that for my second floor but I think it may be too expensive.
 
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Old 11-01-09, 07:42 AM
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Nice project.

For something of that scale, and the planned tightness of the envelope, IMHO it would be well worth the money to have a heat loss and IAQ assessment done by a pro.

Some non-boiler related thoughts, in no particular order.

) site drainage is going to be hugely important at that site. As you get more in to the site work / landscaping, try to get the surface flow moving away from the building as much as possible. In addition to the french drain in the basement, you might also consider an exterior perimeter system.

) when you foam a house, you are turning it into an igloo cooler. You will need to pay attention to indoor air quality (IAQ), particularly with kids. Smart vents, or heat/energy recovery ventilator, etc. will be needed. You want a pro to go over options and do the design for this.

) radon. If radon is an issue in your area, it is even more of an issue with your natural stone foundation. You will have an igloo cooler with an open bottom accumulating radon. This can be partially addressed by the IAQ system, but you might also need a dedicated radon system. My suggestion would be to pipe for one while you have everything open, then when the house is reasonably complete do a radon test to see if you need to install.

So what kind of heating system is being contemplated? At this point, the world is your oyster (except for the budget, but even then, there's a lot you could do here).
 
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Old 11-01-09, 08:55 AM
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I'll ive the supply company a call to see if they will go out and do it for me.
For drainage I was planning a footing drain eventually. just did the drain inside as this spring was very wet and the basement was more like a mud pit. had to get it dried out so i could pour the footers for the columns.
Never really thought of radon. dont believe its a real issue around here but I will defiantly check it out. I would appreciate it though if you didnt keep adding thins for me to do.
I was plannin a mod/cond propane boiler. Likely a TT solo 110 with an smart 50 Indirect DHW. we are going to use as many of the existing Cast iron radiators as we can. then maybe some radiant in the kitchen area.
 
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Old 11-01-09, 10:29 AM
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Originally Posted by dings View Post
I was plannin a mod/cond propane boiler. Likely a TT solo 110 with an smart 50 Indirect DHW. we are going to use as many of the existing Cast iron radiators as we can. then maybe some radiant in the kitchen area.
Excellent plan.
...................
 
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Old 11-01-09, 07:39 PM
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Finished up the heat loss with Heat Load Pro and came up with 74k btu doing a room by room. Then I did a quick whole house one just using the total outside dimensions for my sq ft area and inputting the windows and doors. the diff of the 2 was less than 1000 btu. so at least if I messed up I was consistent about it Beer 4U2
 
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Old 11-02-09, 04:23 AM
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2500 square feet and 74000 btu/hr is ~30 btu/hr/sf. No way. Not a totally foamed house in CT.

For a proper Manual J calculation, you ought to be around 35,000-45,000. Definitely not more than 55,000.

And the actual heat loss will be about 25-30% less than the Manual J.

What outdoor design temperature are you using? Most of CT is in the 5-10F range.

How are you specifying the wall and ceiling assemblies? Are you heating the basement?
 
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Old 11-02-09, 05:55 AM
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I used an outdoor design temp of 2f. I did specify the wall and ceiling assy. the walls are 2x4. the ceilings/roof are 2x6. 1/2" sheetrock on the walls with 3.5" of foam(r21) 5/8" wood siding(the old siding) and vinyl siding with a total effective r of 10.6 for the walls according to the program. the roof i did sheetrock, 5.5" of foam, plywood and shingles. I used a basement temp of the basement at 50f.
Later when I get home I'll see about puttin up the dimensions.
 
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Old 11-02-09, 06:48 AM
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xiphias is doing a good job, but I want to comment on your wall r-value. If you install r-21, plus the drywall, sheathing and siding, you are starting with over r=22. I don't understand how you get all the way down to r-10.6 for an effective value unless they are including doors and windows. Framing materials should be in the range of a 25% reduction, r=22 down to an effective r=16.5.

Also, check to see if you need a plastic moisture barrier above your ceiling sheetrock before they apply that much foam. Not a lot of experience in this, but I would be concerned about the amount of moisture and it's effect on the sheetrock. Besides, if you share the answer with us then I will know.

Bud
 
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Old 11-02-09, 08:17 AM
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the program I am using is what takes the materials and converts them to effective r value. 10.6 seemed a little low to me as well.
according to the building inspector no need for a moisture barrier with closed cell foam but i'll double check. he says there are no moisture issues when fillin the cavity with foam, thats the reason theres no need to vent the rafters (i know this is hotly debated but i asked him about venting and he said dont do it)
 
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Old 11-02-09, 09:29 AM
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I'm one of the dissenters when it comes to not venting. If the attic space is or will become conditioned space, then foaming the rafters and not venting becomes a topic to discuss.

If my memory is working, I believe you said you were foaming the ceiling joists, not the rafters above. If that is the case, then the attic should be vented, although it will not need as much as a leaky home. Without venting, your summer heat will cook that attic and winter sun will raise the temp enough to create ice conditions. I assume living in Ct you are familiar with those blasted ice problems. I'm farther north so not really sure how bad you get them down there.

But, as stated, my memory may be off.

Bud
 
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Old 11-02-09, 03:19 PM
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maybe were a little over 2500 sqft but this is the footprint of the house. picture it in 2 parts
1: 25x30ft 3 floor cape. the third floor has 2 finished rooms (or they will be again eventually) but like a cape the roof is the ceiling.
2: a 20x20ft section that houses the kitchen/eat in area. an 8x20 section in the kitchen has a sloped ceiling that is also the roof over that area. on the second floor is a 20x12 room that will be the master bedroom. then the roof on that area is over the master.
the basement consists of the 25x30ft area as well as the 20x20ft area.
i was going to foam the rafters, which in part of the kitchen as well as the third floor, they are part of the ceiling as well. the only roof that does not come in contact with an actually living area is the one over the master bedroom. I was going to foam those as well.
Hope this clears up some of the confusion I have created so far
 
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Old 11-02-09, 03:52 PM
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Will digest later. But keep in mind that with a TT 110 and an indirect the heat loss is less for sizing the boiler than figuring out the relative amount of radiation you have in each room. Since you're going to reuse the cast iron radiators, this might become further moot if the original relative sizing was correct in the first place. It will also be somewhat important for doing the radiant calcs for the kitchen, and adding any new radiation (and to do that it would be ideal to keep the same relative oversizing as the cast iron).

The cool thing (pun intended) is that with the new building envelope, the cast iron is going to be way oversized relative to the heat loss, so you can run at highly-efficient, low condensing water temperatures. Possibly all year.
 
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Old 11-02-09, 06:49 PM
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Originally Posted by xiphias View Post
Will digest later. But keep in mind that with a TT 110 and an indirect the heat loss is less for sizing the boiler than figuring out the relative amount of radiation you have in each room. Since you're going to reuse the cast iron radiators, this might become further moot if the original relative sizing was correct in the first place. It will also be somewhat important for doing the radiant calcs for the kitchen, and adding any new radiation (and to do that it would be ideal to keep the same relative oversizing as the cast iron).

The cool thing (pun intended) is that with the new building envelope, the cast iron is going to be way oversized relative to the heat loss, so you can run at highly-efficient, low condensing water temperatures. Possibly all year.
so I shouldn't worry about the TT110 being to big?
 
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Old 11-02-09, 07:25 PM
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You might be able to do a Solo 60. But I would ask the nice people at TT about how it would perform with a Smart 50 indirect. On propane.
 
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Old 11-03-09, 05:41 AM
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I was kinda thinking the 60 would be too small for the indirect. I'll just stick with the 110 and stop worrying about it
I'll be back once its time to figure out the layout of the systemBeer 4U2
 
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Old 11-03-09, 06:19 AM
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It would definitely be worth a call to TT to ask. On priority with a couple of the DHW parameters tweaked it might be just fine. The modulation range of the 60 is definitely better suited to your probable situation.
 
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Old 11-03-09, 03:34 PM
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sent TT an email. Didnt get to call them until after business hours. Looking at the specs the tt110 propane modulates down to 25k btu while the solo60 modulates down to 16k btu.if the 60 would work is that 9kbtu diff on the low end going to amount to much savings? the cost diff between the 2 isnt that big. The 110 shouldnt use 100% of its power if its not called for right?
Not tryin to justify the 110 over the 60, just wondering.
 
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Old 11-03-09, 05:55 PM
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For a good part of the year, chances are that your heat loss will be less than the minimum modulation, particularly for the 110. That will lead to cycling, which if avoidable should be avoided.

16k is 35% lower than 25k. That's a useful amount.

There is also some allowable wander in the modulation specs. I know of at least one 110 that only goes down to about 32k.

The major thing that would swing me for the 110 over the 60 is if TT said that the 60 really can't fire an indirect effectively to meet the demand of a typical family of four. (Although I'm a bit of an energy/water nut and would probably alter water use patterns to allow the use of the 60....)
 
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Old 11-03-09, 06:26 PM
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For all around maximum fuel savings, less maintenance, comfort and overall cost try to match the heat loss to the DOE output. Oversizing will short cycle the boiler and lower efficiency.
 
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Old 11-04-09, 03:28 PM
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Well TT emailed me back about usin the solo 60 with the smart 50. This is what they said
"It will work. The gallons per minute flow will be based on the domestic rise. Example-cold in, hot out has a 70 degree difference. 500 times 70 -35000 boiler output 54000 –you will be able to flow 1.5 gpm.. call in for more help if needed."
I though it was pretty cool they got right back to me and even offered more assistance. guess i'll have to get cracking on getting accurate heat loss numbers.
is 1.5gl min. enough so when the wife decides to run the dishwasher and washing machine while i'm in the shower i'll be good.

On another not regarding the closed cell and vapor barrier, this is what my building inspector emailed back
"Sorry for the delay in getting back to you, I'm in Baltimore, MA participating
in the code hearings. An additional vapor barrier (vb) is not required for
closed cell. Closed cell has the required water permeability rate. Yesterday I
want to two different manufactures representatives and they agree that no
additional vb is required for closed cell.

On another matter, if you wish to use open cell. I asked two different
manufactures representatives about open cell I get a different response. Their
response was, open cell is an insulation and not manufactured as a vb and has no
comment. Not much help for me. My understanding is that open cell doesn't meet
the water permeability rate by it's self. "
 
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Old 11-05-09, 04:26 AM
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Although I've stared and stared and worked and worked to understand indirect sizing and recovery, I still think it's something of a dark art....

Let's see if this sounds right. It may be not at all.

Typical showerhead draws 2.5 gpm. Call it all hot, so it's kind of an overestimate, but not hugely.

Smart 50 holds 50 gallons. Of that, about 80% is 'usable' before the boiler needs to start recovering it. Call it 40 gal.

40 gal / 2.5 gal per min = 16 min

You can take a 16 min shower (about double the average shower) before the boiler needs to get going.

Now the boiler needs to recover the tank. It probably has to do about a 60F rise to get the whole 50 gal back to 120 (or 140, because that's what I'd do, with an anti-scald tempering valve on the output).

50 gal is 407 pounds of water. It will take 24k BTU to heat 407 pounds of water 60 degrees. At 54k output, that's 27 minutes to fully recover the tank.

50 gal * 8.33 lb/gal * 60F = 24k btu

( 24k btu / 54k btu ) * 60 min/hr = 27 minutes

So, if that's even in the ballgame, that should give a decent recovery between major draws. It would take a bit longer but you'd have more effective reserve capacity if the tank runs at 140.

Seems ok to me. 20 minutes or so of not heating the house won't cause much if any change in space temperature. Just need to make sure your 'dump load' isn't too great (e.g., running the dishwasher and laundry while taking a shower can't draw down the tank in less time than it takes to get a reasonable shower). Prolonged draws (>20 minutes) of more than 1.5 gpm will be a problem, I think. Shouldn't be an issue unless you're trying to fill a soaking tub or whatever.
 
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Old 11-05-09, 05:52 AM
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Originally Posted by xiphias View Post
Although I've stared and stared and worked and worked to understand indirect sizing and recovery, I still think it's something of a dark art....

Let's see if this sounds right. It may be not at all.

Typical showerhead draws 2.5 gpm. Call it all hot, so it's kind of an overestimate, but not hugely.

Smart 50 holds 50 gallons. Of that, about 80% is 'usable' before the boiler needs to start recovering it. Call it 40 gal.

40 gal / 2.5 gal per min = 16 min

You can take a 16 min shower (about double the average shower) before the boiler needs to get going.

Now the boiler needs to recover the tank. It probably has to do about a 60F rise to get the whole 50 gal back to 120 (or 140, because that's what I'd do, with an anti-scald tempering valve on the output).

50 gal is 407 pounds of water. It will take 24k BTU to heat 407 pounds of water 60 degrees. At 54k output, that's 27 minutes to fully recover the tank.

50 gal * 8.33 lb/gal * 60F = 24k btu

( 24k btu / 54k btu ) * 60 min/hr = 27 minutes

So, if that's even in the ballgame, that should give a decent recovery between major draws. It would take a bit longer but you'd have more effective reserve capacity if the tank runs at 140.

Seems ok to me. 20 minutes or so of not heating the house won't cause much if any change in space temperature. Just need to make sure your 'dump load' isn't too great (e.g., running the dishwasher and laundry while taking a shower can't draw down the tank in less time than it takes to get a reasonable shower). Prolonged draws (>20 minutes) of more than 1.5 gpm will be a problem, I think. Shouldn't be an issue unless you're trying to fill a soaking tub or whatever.
sounds good to me now can you explain it to my wife
redid the heat loss last night re figuring the effective r values to where they should be and using .2 for the air infiltration and got it down to 54kbtu. Looks like i'll give the solo 60 a shot. Started lookin at the buderus 84k btu boiler but it doesnt modulate down much less than the solo 110 so i wont do that. Changed the design temp in the heat loss to see what it would be at 45 degree outdoor and its just over 16k so i think that solo 60 will work out well
 
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