# Calculations for Sizing a Furnace

### Calculations for Sizing a Furnace

This sizing calculation can be used to give you an approximate furnace size because local climate, house design features, and other factors may have an overriding influence on the heat demand. Also most solid fuel central furnaces can be installed 10 to 20 percent smaller than conventional systems because the heat output in continuous.

Winter Design----------------------------------Insulation Level------------------------
Temperature *F.--------Poor-----------------------Medium----------------------Good

-20-----------------------136----------------------------85----------------------------34
-10-----------------------120----------------------------75----------------------------30
0--------------------------104---------------------------65----------------------------26
10-------------------------88----------------------------55----------------------------22
20-------------------------72----------------------------45----------------------------18
30-------------------------56----------------------------35----------------------------14

The size of the furnace needed is related to the floor area, an average heat loss factor for the home, and the section of the country you live.
Calculate the total floor area of the home. Add in the second floor area if your home is two stories. Now multiply the floor area times the heat loss factor to get the approximate size furnace needed.

For example, a poorly insulated home that has a heat loss factor of 104. If the first floor is 1,000sq.ft. and the second floor is 700sq.ft., the heat loss on the coldest day at 0* will be:

1000sq.ft. + 700sq.ft. X 104 = 176,800 BTU's per hour

I thought this was a neat calculation to play with. Try it out for yourself. DOUG
DOUG

Stove/Furnace Make: CHUBBY, D.S.MACHINE BOILER
Stove/Furnace Model: CLAYTON 1600