Help needed w/heat loss calculation...

john p_2

Trying to help a friend out and myself to understand heat loss a little better, maybe someone can shed some light on this for me.

Did a calculation on the US Boiler Company website and all results posted below but I don't understand...what/why is a range of temperatures given?

And by the way this calculation was being done for a possible garage unit heater in a 30' X 30' & 8' ceilings w/6" insulation

Total Heat Loss for 60 F Temp. Diff. = 31,209.00
Total Heat Loss for 70 F Temp. Diff. = 36,826.62
Total Heat Loss for 80 F Temp. Diff. = 41,820.06
Total Heat Loss for 90 F Temp. Diff. = 46,813.50
Total Heat Loss for 100 F Temp. Diff. = 51,806.94

BobC

Different areas of the country have differed design temperatures (minimum expected).

The temperature difference is between desired room temperature ( 70 degrees for a house) and the expected minimum temperature for your area (in my area it's 5 degrees).

Bob

john p_2

Thanks so much Bob

BobC

Your welcome. Don't ever be afraid to ask a question - someone on the forum will have an answer.

Bob

Ironman

36,826 btus = almost 41 btus per sq. ft. That sounds awful high.

I would recommend that you down load SlantFin's heat loss app and use that. It will be a lot more accurate.

Online calculators will grossly over-size.

john p_2

I actually have the SlantFin & Taco's but found the US Boiler one and thought it might be a little easier for my friend to use and see for himself what kind of things go into a heat loss calculation.
It is a garage on grade with uninsulated walls and two large garage doors.

Georgi

Formula: Heat Loss Through a Building Component = U-Factor x delta T x Area

U factor is reverse on R factor. R Factor is cumulative of the thermal resistance of every component of the wall - sheeting, insulation, sheetrock or other interior finish. Add the R values for all of them. Then reverse as a fraction. For example if total R value is 18, then U value is 1/18. If R=25, then U=1/25.

Delta T is the difference between the temperature outside and the temperature you want to maintain inside. Usually 65 F is used as a standard for indoor temperature. So if it is 20F out, delta T = 65-20=45. This is why the calculator you used gave you multiple options.

Area - calculate all external walls and possibly ceiling. If the garage is detached (all walls and ceiling are external), then your area is 4 walls 30x8 + ceiling 30x30. If the garage is attached to a house, only 3 walls and a ceiling will be external. If the garage is part of the house, then only one wall is external.

The number you get is your heat loss measured in BTU/hour. This is conductive heat loss through materials. Convective heat loss (through holes and gaps) is separate formula.

Kind of late response, but I just recently found this forum. Maybe it will help somebody in the future.

Rich_49

Maybe there is someone in your area that knows how to do such things .