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# Determine Furnace size by Heat Loss/Gain

## Determine Furnace size by Heat Loss/Gain

#1
10-11-08, 01:06 PM
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Join Date: May 2007
Location: New York
Posts: 270
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Determine Furnace size by Heat Loss/Gain

Could anyone tell me how to determine the size furnace I need according to the following info:

House Size: 2400
House Style:Colonial

Total Heat Gain: 33,047 BTUH
Total Heat Loss: 84,163 BTUH

The existing furnace is 165,000 BTU but it is well oversized. Any help is Greatly appreciated....

#2
10-11-08, 03:23 PM
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Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Furnace size

You need a furnace with an output large enough to cover the heat loss (+/- 85,000 btu/hr). If you use a 90+% efficient furnace you'll likely end up with one with an input of 100,000.

#3
10-11-08, 06:42 PM
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Join Date: May 2007
Location: New York
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So I should probably go a little larger, correct? Like 110,000 or 115,000?

#4
10-11-08, 07:46 PM
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Join Date: Dec 2005
Location: VA
Posts: 5,491
No longer run times = better money savings

#5
10-12-08, 01:03 AM
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Join Date: Mar 2004
Location: NA
Posts: 1,830
84k is a bit high for 2400 sq ft. unless you live in a really cold climate.

Do everything you can to reduce heat loss prior to replacing the furnace. (Draft proofing should come first, followed by adding insulation)

#6
10-12-08, 09:44 AM
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Join Date: May 2007
Location: New York
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I live in New York State -it's cold. My info comes from a Free Heat Loss Estimate from http://www.hydronic.net. To double check it, does anyone know where I can get the Heat Loss Formulas to calculate them myself??? I am a math person as well as a programmer so I'd like to double check the accuracy of their software...

#7
10-12-08, 03:09 PM
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Join Date: Jan 2005
Location: Delaware, The First State
Posts: 12,682
Heat loss/gain calculations

There is a free heat loss program available from Slant Fin.
http://www.slantfin.com/heat-loss-software-get.html

I don't know of any free heat gain programs but one of the best costs \$50 & is available here: http://hvaccomputer.com
It does heating & cooling.