heat loss calcs and thermostat setback energy savings

George Durisek

Performed a heat loss calculation for a residence.
Inside design Temp. 70 F
Outside Design Temp. 0 F
Heat loss 104,580 BTUH

Annual Fuel Useage 133.66 MMBtu/year

Customer would like to know if he sets the thermostat back to 68 F, or 65F what would the annual savings be. I'm interested to finding out how to correlate the data at design conditions to the set back values stated above. If I re-calculate the heat loss at an inside design temperature of 68 F. The value of the heat loss calculation is lower as expected, but plugging the new heat loss figure and inside design temp. into the annual useage formula gives the same annual useage value when I calculted with the original design conditions. I see that the values are proportional to each other. I'm Looking for someone to point me in the right direction to perform this analysis.

Thanks George