For example if you re trying to heat 1000 square feet in a cold climate 30 000 40 000 btu s will add significant warm air to your home.
60000 btu furnace square feet.
A furnace putting out 60 000 btu s per hour will probably handle the heating load even though your house is most likely uninsulated and in a very cold climate.
With these numbers you can calculate your furnace btu.
But before we buy an 80 000 btu furnace there s furnace efficiency to consider as well.
A mid sized home of 2 000 square feet would need approximately 50 000 to 60 000 btu to heat it properly.
But there are also rule of thumb estimations you can use to pick a furnace size for your home.
For this example using an 80 efficient furnace the 1900 square foot home above would require a 90 000 btu input furnace that produces 72 000 btu s of heating which is close enough to the 76 000 btu s required using the climate heating factor.
And in cold climates multiply the square foot number by 30 40.
Furnaces are rated on their btus of energy consumption not their btus of energy output.
Your heating bills will probably be sky high though.
You might want to plan to invest in upgrading the insulation putting in new windows and weatherstripping around the doors.
A more efficient furnace will output more btus of heat than a less efficient furnace with the same btu rating.
For example if a furnace is rated at 100 000 btus and is 80 efficient then the heat output will be 80 000 btus 100 000 x 8.
A 60 000 btu furnace will adequately heat most mid size family homes in zone 1 and zone 2.
On the other hand the colder zone 5 climates of the northeast upper midwest and pacific northwest demand 50 60 btus per square foot for maximum efficiency.
Another quick and easy way to estimate the number of btu s required is with this helpful chart.
For cooler climates a very broad estimate of furnace sizing is to select one that generates 40 to.