Could anyone help me calculate a breakdown that shows  heat loss in BTU/hour that adds up to 100% and shows % or subtotals for the sub-categories that add up to 100% based on  u values and Area for the sub-categories I guess per square foot of area in question. For a stated day with stated temperature inside of 70 degrees and outside temperature of 40.
The areas in questions are: 
-Ceiling. with an R4 value of insulation
-1st Floor to unconditioned basement 2x8 empty cavity, 3/4 pine groove plus 1/2 hardwood -No insulation
-Windows/Glass casement windows double pan glass
-Exterior Walls with 3/4 pine siding, 3/4 insulation, 1/2 drywall
-Air change
I would be grateful for any advice you guys could provide!

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Answer equals = U * A * T

As you are missing A or area.... for the first one

What the Delta T & A is for the second

What the U value & A are for the third & fourth...

Your question asked is impossible to answer - you fill in the blanks & you have your answers

I was thinking that in order to stay away from a full blown home calculation, I would keep it simple so I could learn the concepts. I suggested a one square foot of the material, temperatures ranges are 40 outside to 70 inside. 

Knowing the area (one square foot) and knowing the temperature range... Can I figure the rest?


Hi Luis,

It gets a lot more complicated than what you are asking for, but learning is something a lot of people should be doing. 

Your one ft² example will give you an idea as to the heat loss per foot in one hour, but only for the given temperature.  If you want the loss per year, you add in the heating degree days.

Sean's equation Q = U x A x ▲T gives you the btu's for the area and the u-value specified.

If you want to estimate the energy lost for a year, use: Q = U x A x HDD x 24.

If you want to play with a very basic heat loss calculator, try Gary's over at build it solar:




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