Need sizing formula

[gregl]

I found a thread on this board with a sizing formula, but of course I can't find it now. I've been to a dozen Web sites and have come back with size answers ranging from 14K BTU to 155K BTU for the same space using the same data input.

So can someone please point me to a formula to calculate what size heater I'll need. THANKS!!

Most of the generic tricks don't work for me because I'm in Central California and only need about a 30 degree rise from outside temps -- not nearly the problem that some of you have. The shop is 24 x 45 and will have insulation to about R6. I'd like to heat the space up those 30 degrees in about an hour and a half first thing in the morning and then hold it there for the day. It's the mornings that are the problem; coldest afternoon outside temps are usually at least in the low 40s so most any heater will hold that. But when it's 38 inside the shop at 10:30 a.m. I just don't want to be there.

So any direction to a formula that will work for these circumstances is appreciated. THANKS again!

 

[Sokoloff]

You need to do a "Manual J" calculation for heat load. SlantFin has a free calculator available for download that works well. I couldn't find a direct link, but I recall it was very easy to find on their site.

Be aware that "doing it right" is far more complex than a simple formula of square footage * some weather information. The detailed calcs take into account wall construction, window sizing and placement, etc.

 

[gregl]

Thanks, Sokoloff, I'll look for that. Sounds like just what I need. I've had all sorts of answers from wild guesses from salesmen to weird results from various Web sites that seem to be more appropriate for someone in Minnesota than here in relatively warm Central. Calif. Thanks again.

 

[D KRAGER]

http://www.heatershop.com/btu_calculator.htm

 

[benjamming]

D_KRAGER,

I don't see where they define what is average, good, & poor insulation so there is quite a big of error likely in using that calculator.