# Formula for Calculating Heat Output

### Formula for Calculating Heat Output

How do I figure out how much heat I'm getting from my furnace? Lets say my cold air return is 67 degrees and my warm air duct is 107 degrees. Lets also say my blowers are pushing 1000 cubic feet per minute. What is the net output in BTUs per hour?
Lightning

Hand Fed Coal Furnace: Overmodified/Bored out Clayton 1537
Coal Size/Type: Anthracite/Awesome Size

### Re: Formula for Calculating Heat Output

I know I'm just getting older & goofier as time goes on, but would not the calculations of, my house being consistantly warm (73*) & I spend about 1/3 the money on coal as I would on heating oil/kero be a pretty good BTU factor Just curious I guess.
freetown fred

Hand Fed Coal Stove: HITZER 50-93
Coal Size/Type: BLASCHAK Nut

### Re: Formula for Calculating Heat Output

Take the lbs of coal you burn per day multiply by the average BTU per lb (12500 ?) and divide by 24.

ex 50lbs x 12500 = 625000/24 = 26041

26041 x .70 = 18,228btu per hour

Eric

works for me
Coalfire

Hand Fed Coal Stove: DS Machine 96K btu Circulator
Coal Size/Type: Nut

### Re: Formula for Calculating Heat Output

freetown fred wrote:I know I'm just getting older & goofier as time goes on, but would not the calculations of, my house being consistantly warm (73*) & I spend about 1/3 the money on coal as I would on heating oil/kero be a pretty good BTU factor Just curious I guess.

I get what yer saying partner just curious if my cantankerous tinkering and techniques are yielding positive results based on the numbers. I'm kinda a science guy lol, I do appreciate your post!
Lightning

Hand Fed Coal Furnace: Overmodified/Bored out Clayton 1537
Coal Size/Type: Anthracite/Awesome Size

### Re: Formula for Calculating Heat Output

Eric,
Thanks for your input! Actually, my next step is to determine efficiency based on coal usage verses heat output
Lightning

Hand Fed Coal Furnace: Overmodified/Bored out Clayton 1537
Coal Size/Type: Anthracite/Awesome Size

### Re: Formula for Calculating Heat Output

I have a feeling that possibly farming keeps one pretty busy 24/7 & has been running on the "if it ain't broke theory for a real long time. BUT, I do understand your curiosity, that does not mean I'm not going to goof on ya. I have a brother in law that is a minute' partical physicist--he also is the curious type.
Lightning wrote:
freetown fred wrote:I know I'm just getting older & goofier as time goes on, but would not the calculations of, my house being consistantly warm (73*) & I spend about 1/3 the money on coal as I would on heating oil/kero be a pretty good BTU factor Just curious I guess.

I get what yer saying partner just curious if my cantankerous tinkering and techniques are yielding positive results based on the numbers. I'm kinda a science guy lol, I do appreciate your post!
freetown fred

Hand Fed Coal Stove: HITZER 50-93
Coal Size/Type: BLASCHAK Nut

### Re: Formula for Calculating Heat Output

Lightning wrote:How do I figure out how much heat I'm getting from my furnace? Lets say my cold air return is 67 degrees and my warm air duct is 107 degrees. Lets also say my blowers are pushing 1000 cubic feet per minute. What is the net output in BTUs per hour?

The simplified formula for air is - BTUH = CFM x 1.08 x delta T (deg F)

So

1000 cfm x 1.08 x 107-67 = 43,200 btuh.

Word of caution. You need to know the actual air flow not just the "rated" air flow. Fans ride on a curve against static pressure resistance just like a pump rides against system friction loss. You need test instruments and some knowledge/training to read actual air flows.
steamup

Stoker Coal Boiler: Axeman-Anderson AA-130, Keystoker K-6
Hand Fed Coal Boiler: HS Tarm 502 Wood/Coal/Oil
Coal Size/Type: pea, buck, rice

### Re: Formula for Calculating Heat Output

I see... Yeah that number for BTU per hour exceeds the coal I'm putting in it. I just figured that if I have dual 550 CFM blowers then I ought to get a 1000 CFM. But guess not lol. Thanks for the formula though!!
Lightning

Hand Fed Coal Furnace: Overmodified/Bored out Clayton 1537
Coal Size/Type: Anthracite/Awesome Size