FIND YOUR HHI
Determine your average annual gas usage either in therms or BTUs (1 therm = 100,000 BTUs).
Find the lowest use month (usually July or August), multiply by 12 and subtract that from your annual usage. This accounts for your base uses such as water heating. The remaining is primarily space heating.
BTUs/sq.ft./5466
example:
annual gas consumption is 714 therms
lowest consumption is in August, 11 therms
annual heating load would be 714 - (12x11) , 582 therms or 58,200,000 BTUs
house is 2032 sq. ft.
58200000/2032/5466=5.24
0-3
Well- insulated and airtight
high performance windows and heating system
3-6
Better than average, good insulation
moderate air leakage, good heating system
6-10
Average home, average insulation
fairly leaky, adequate heating system
10-15
worse than average, little insulation
quite leaky, inefficient heating system
15+
Older home, poor or no insulation
very leaky, poor heating system