furnace sizing guide

Furnace Sizing Calculator: What Size Furnace Do I Need?

How many BTU furnace would fit your home perfectly? Most homeowners have difficulties figuring out what size of furnace do they need. Fortunately, calculating furnace size (be it natural gas, propane, or oil) is not rocket science.

To help future furnace owners out, we have developed a simple furnace sizing calculator. You only need to know two things; your home square footage and the climate zone you’re in. 

After the furnace sizing calculation, you’ll find how the size of the furnace is calculated. We also made 3 examples for:

  1. What size furnace do I need for a 1000 sq ft house? (Example 1)
  2. What size furnace do I need for a 2000 square foot home? (Example 2)
  3. What size furnace do I need for a 3000 sq ft home? (Example 3)

For an exact estimation of furnace size, you should ask your local furnace installers. You can 

Furnace BTU Calculator (Input Square Footage And Climate Zone)

0.00 BTU

Furnace Capacity


You can freely use the calculator to roughly estimate the capacity of a furnace you need.

The basic principles the furnace sizing calculator is based on are:

  • Larger homes need more BTU than smaller homes (directly proportional to square footage).
  • Homes in colder climates (Region 5; Example ) need to generate more heat than holmes in warmer climates (Region 1; Example

In order to properly size a furnace, we need to use BTU heating needed per square foot for each climate zone:

Region 1Region 2Region 3Region 4Region 5
35 BTU per sq ft40 BTU per sq ft45 BTU per sq ft50 BTU per sq ft60 BTU per sq ft

Essentially, homes in the far North (Minessota, for example) need almost twice as much heating as homes in the far South (Texas, for example).

Here are the 3 examples that illustrate how the calculator works.

What Size Furnace Do I Need For A 1000 Sq Ft House? (Example 1)

Let’s say we have a nice 1,000 square foot home in Los Angeles, California. We need two data points:

  1. Home square footage: 1,000 sq ft.
  2. Climate zone: Los Angeles, California, is in Region 2.

We input both of these data points in the calculator. Here is what we get:

for 1000 sq ft home we need 40000 btu furnace

In short, we need a 40,000 BTU furnace.

What about if we have a 1,000 sq ft home in the heart of Minnesota? That’s Region 5. Here is what we get with the furnace sizing calculator:

in cold climate 1000 sq ft home needs 60000 btu furnace

We see that for a 1,000 sq ft home we need:

  • 40,000 BTU furnace in California.
  • 60,000 BTU furnace in Minnesota.

Here are the results for 1000 square foot houses in all climate zones:

Region 1Region 2Region 3Region 4Region 5
35,000 BTU40,000 BTU45,000 BTU50,000 BTU60,000 BTU

What Size Furnace Do I Need For A 2000 Square Foot Home? (Example 2)

2000 sq ft houses need double the furnace capacity compared to 1000 sq ft house.

Here are calculated 2000 sq ft home estimates for furnace size:

Region 1Region 2Region 3Region 4Region 5
70,000 BTU80,000 BTU90,000 BTU100,000 BTU120,000 BTU

What Size Furnace Do I Need For A 3000 Square Foot Home? (Example 3)

Furnace size for a 3,000 square foot home range from 105,000 BTU to 180,000 BTU, depending on the climate zone you’re in. Here is a table with calculated 3,000 sq ft furnace sizes for all 5 regions:

Region 1Region 2Region 3Region 4Region 5
105,000 BTU120,000 BTU135,000 BTU150,000 BTU180,000 BTU

We hope everybody will be able to use the furnace capacity calculator and get a good estimate of the size of the furnace they need for the winter heating

You can check our articles about different types of heating furnaces:

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