Question

Given a wall that is 36 feet long and 8 feet high calculate the heat loss per hour when the inside temperature is 70 degrees inside and 10 degrees outside.

The wall assembly consists of:

A = Face brick

B = 1” Polystyrene ins. board

C = 2 X 6 studs

D = Fiberglass batt ins.

E = ½” Sheet rock

F = Paneling

Answer 1

In construction industry, the problems of heat transfer are solved by taking into consideration the R-values of materials used for construction. R-value is basically the measure of thermal insulation in the house.

The R-values of materials in the wall assembly for the above problem are:-

Face brick, R₁ - 0.44 Ft2*F*hr/BTU

1” Polystyrene ins. board, R₂ - 5 Ft2*F*hr/BTU

2 X 6 studs, R₃ - 6.85 Ft2*F*hr/BTU

Fiberglass batt ins., R₄ - 13 Ft2*F*hr/BTU

½” Sheet rock, R₅ - 0.45 Ft2*F*hr/BTU

Paneling, R₆ - 13.7 Ft2*F*hr/BTU

Total R- value = 39.44 Ft2*F*hr/BTU

Area = 36*8 Ft² = 288 Ft2

Heat Loss/hr = (Area * Temperature difference) / Total R-value

                         = [ 288* (70-10) ] / 39.44

                         = 438.13 BTU/hr

The heat loss per hour from the given wall is observed to be 438.13 BTU/hr.