Heat loss calculation


  #1  
Old 09-30-19, 07:25 AM
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Heat loss calculation

I did the boiler heat loss calculations using the calculator on the US Boiler Company web site. I have some numbers but I don't know how to determine boiler size based on those calculations.

This is what I came up with -

Heat loss -
Windows and doors - 5,160
Net Walls - 8,740
Ceiling - 1,728
Floor - 3,456
Infiltration - 1.07

Total heat loss 60* temp differential - 19,085
" 70* " - 22,520
" 80* " - 25,574
" 90* " - 28,627
" 100* " - 31,681

How does that translate to boiler size (MBH)?
 

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10-01-19, 07:04 PM
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lawrosa
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2200 sq ft home you would be in the 55k btu for a boiler...If your well insulating probably lower..

You didnt reply to the other thread about the indirect.. I posted about that HTP product..

I would install a simple burnham boiler.. Although peerless are alright too.. But Id have to see what controls are on the current boilers..

I would assume you have two zones?

There is a lot to consider.
What heat emmitters are they using>
Can or should you over radiate to run lower boiler temps>
Should you spend more and go modulating boiler>
Possible put a combi in, that also does hot water> Think tankless..

etc etc..

But you need a proper heat loss to be sure..

The simple math calculation comes close.. All boilers have a fudge factor. ( larger then they actually are)

I would assume a 50k btu boiler would suffice..

Most boilers are oversizd. Installers are scared to size correctly because they dont know or dont care.

https://www.usboiler.net/product/ser...s-water-boiler
 
  #2  
Old 09-30-19, 02:23 PM
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Where are you located? We need to know the design outdoor temperature. From your info, you must have a very small house. You may not readily find a boiler that small. What is the sq ft? How is the house now being heated and what is the boiler size? Photos would help us understand your situation.
 
  #3  
Old 10-01-19, 06:05 AM
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I'm in southern New England. I may have screwed up the heat loss calc. The house is 2 story, 2200 s/f, 2X4 construction currently gutted to the studs. New insulation will be foam R-15 or R-19. Attic will be insulated to code. All glass is double pane. I don't know what "design outside temperature is." I think my current boiler is Peerless. I don't know the MBH rating.

One of the contractors that has submitted a proposal is recommending an 80,000 BTU boiler. He did not do a heat loss calc. Said he only needed to look at the house to determine the boiler size.

I just Googled design temp for my zip code . For heating it is between 8 - 9. No idea what the units are.
 
  #4  
Old 10-01-19, 09:20 AM
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Your heat loss calc is clearly in error. Try again, using one of the programs linked as a sticky on this forum.
 
  #5  
Old 10-01-19, 07:04 PM
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2200 sq ft home you would be in the 55k btu for a boiler...If your well insulating probably lower..

You didnt reply to the other thread about the indirect.. I posted about that HTP product..

I would install a simple burnham boiler.. Although peerless are alright too.. But Id have to see what controls are on the current boilers..

I would assume you have two zones?

There is a lot to consider.
What heat emmitters are they using>
Can or should you over radiate to run lower boiler temps>
Should you spend more and go modulating boiler>
Possible put a combi in, that also does hot water> Think tankless..

etc etc..

But you need a proper heat loss to be sure..

The simple math calculation comes close.. All boilers have a fudge factor. ( larger then they actually are)

I would assume a 50k btu boiler would suffice..

Most boilers are oversizd. Installers are scared to size correctly because they dont know or dont care.

https://www.usboiler.net/product/ser...s-water-boiler
 
Bud9051, Furd voted this post useful.
  #6  
Old 10-01-19, 08:51 PM
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I just Googled design temp for my zip code . For heating it is between 8 - 9. No idea what the units are.
That reads more like agricultural zone than design temperature. If you have lived there for many years then think how cold it has gotten during the coldest winter and that will be your design temperature.

As for the contractor stating a particular size without doing a heat loss calculation...SOMETIMES a contractor with lots of experience AND with a lot of similar homes in the area can make an educated guess as to the size needed. However, in all cases the contractor will suffer the blame if the house is not adequately heated so HE is very careful to not undersize the heating plant. He is not going to be paying the costs of an oversized heating system so it is in his best interest to oversize.

Also, I agree with all Mike wrote.
 
  #7  
Old 10-02-19, 08:06 AM
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Mike - I appreciate the good info. I redid the heat loss calculation using a different site and came up with just under 50,000 MBH. I also got proposals from two of the heating contractors that have looked at the house. One is proposing a Biasi B10/3 boiler rated at 58,000 BTU (or 80,000 BTU depending which web site I visit) with a Riello burner. The other contractor would install a Burnham boiler with a Beckett burner. Both boilers are 3 stage. Both installs are in the 8K - 10K range. That includes a new tank and baseboard radiators.

I looked around the internet and both boilers had mixed reviews. But then again, I had a hard time finding a boiler that didn't have mixed reviews.
 
 

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