EGEE 102
Energy Conservation and Environmental Protection

Calculating Daily Heat Loss


Now that you know how to calculate hourly heat loss, how would you calculate daily heat loss?

Since there are 24 hours in a day, you would simply multiply the hourly heat loss by 24.

HeatLoss( BTUs h )= Area(f t 2 )×TemperatureDifference ( o F) Rvalue( f t 2 o Fh BTUs ) ×24hr/day


What is the hourly and daily heat loss of a 15-ft by 15-ft room with an 8-ft ceiling, with all surfaces insulated to R13, with inside temperature 65°F and outside temperature 25°F?

Cube, Height = 8 ft, Width = 15 ft, Depth = 15 ft, each side = 120 sq ft.
HourlyHeatLossrate= Q(BTUs) t(hour) = (480f t 2 ×( 65 o F 25 o F ) 13 f t 2 o Fh BTU =1,477 BTUs h

Once we know the heat loss rate per hour, we can determine the heat loss per day by multiplying by 24 (hours in a day).

In a 24-hour period or one day, the heat loss would be:

DailyHeatLossperday= 1477BTUs h x 24h day =35,448 BTUs day
HeatLoss( BTUs h )= Area(f t 2 )×TemperatureDifference ( o F) Rvalue( f t 2 o Fh BTU )

Area (ft2) is the sum of the area of all four walls. Each wall is 8' x 15', or 120 sq. feet, so take 4 x 120 sq ft to get 480 ft2 in the equation.