What Size Furnace Do I Need? | How to Size a Furnace | What BTU Furnace Do I Need?

What Size Furnace Do I Need?

A new build home will need a furnace, and they also don’t last forever, so maybe your old furnace needs replacing. In any case, you may be asking what size furnace do I need? Planning out an HVAC system can be complicated, but this is a calculation that anybody can do. You need a few bits of data and the formula.

How to Size a Furnace in Terms of BTU’s

The calculation depends on your climate for pretty obvious reasons. If you live in a cold place, you’re going to need more muscle to get the job done. If you live in the sunbelt, you probably won’t need as much. The United States is a huge country in terms of geographic size, which means many different climates.

what size furnace map of United States based on BTU output needed
  • If you live in the low desert or the southeast, you only need 30-35 BTUs per square foot.
  • Coastal California requires about 35-40 BTUs per square foot.
  • Homes in the coastal Pacific northwest need about 40-45 BTUs per square foot.
  • The high desert requires 45-50 BTUs per square foot.
  • If you live in the middle mid-west (as opposed to the north mid-west) or middle east coast, you will need anywhere from 40-50 BTUs per square foot.
  • The upper mid-west, New England, and Alpine areas require a whopping 50-60 BTU’s per square foot.

Once you’ve determined what climate you are in, all you have to do is take that recommended number and multiply it by the square footage of your home.

Furnace Size Calculation Example

Say you live in the high desert in a 2,000 square foot home; your calculation would look something like this on the low side:

45 BTU’s per square foot x 2,000 square feet = 90,000 BTU’s

On the high side:

50 BTU’s per square foot x 2,000 square feet = 100,000 BTU’s

You’re going to have to make an executive decision about whether or not you want to play it safe or play it cheap and pick somewhere in that range.

Find Furnace Parts at PlumbersStock

Now that you know what size furnace you need in terms of BTU's, it's time to make other considerations before making a purchase. Check out all our helpful resources. We carry a huge inventory of HVAC parts like blowers, furnace ignitors, blower wheels, etc. Did you know that you can find member pricing here on certain items (typically name brand, MAP priced items) if you log in? For industry professionals buying in bulk, please consider contacting us directly for extra special pricing and extra savings.

Related resources:
How Many Watts Does a Furnace Use?
How to Calculate Heat Load
What Is a Furnace?
Gas vs. Electric Furnace
Furnace Replacement Cost
1-Stage vs. 2-Stage Furnaces

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