For example in zone 3 to 4 which typically requires 40 45 btu per square feet you can determine that a 2 500 square foot home would need a 100 000 to 112 000 btu furnace.
Gas furnace btu for square footage.
For example a furnace with an input btu can have an efficiency of 80.
1 watt is approximately 3 412 btu per hour.
It is approximately the energy needed to heat one pound of water by 1 degree fahrenheit.
Take your home s square footage and multiply it against the btus your climate requires.
This btu calculator will determine what hearth product size is required with only a few steps and information such as square footage sq ft.
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.
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.
That means the furnace will produce 80 000 btu of heat.
At 40 to 45 btus per square foot you d need a 100 000 to 112 500 btu.
Calculate how many btus you need to heat a room or even a house with a wood burning pellet or gas fireplace insert or stove.
If that same furnace has an efficiency of 95 the furnace will produce 95 000 btu of heat.
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.
2 000 square feet x 40 btus 80 000 btu output required.
For cooler climates a very broad estimate of furnace sizing is to select one that generates 40 to 45 btus per square foot.
Average square and cubic footage.
Thanks to the equation we know we need 80 000 btus of heat.
What is a btu.
The british thermal unit or btu is an energy unit.
We included an example for you below.
Furnaces have come a long way in efficiency over the past few decades.
A more efficient furnace will output more btus of heat than a less efficient furnace with the same btu rating.
But before we buy an 80 000 btu furnace there s furnace efficiency to consider as well.
Another variable in determining your energy needs is space both in terms of square footage and cubic footage.
Furnaces are rated on their btus of energy consumption not their btus of energy output.