Boiler Size Calculator: What Size Boiler Do I Need?

Correctly answering “what size boiler do I need” means your residential boiler will be large enough to heat your home and, if it is a combi boiler, provide domestic hot water.

The Boiler Size Calculator on this page is a unique tool to determine the right size boiler.

Boiler Size Calculator

House size is just one factor in sizing a residential boiler. Your geographical location, home’s insulation and whether your weather is sunny or not are factors too.

Boiler Sizing Tip: If you live near the edge of a Zone and aren’t sure which Zone is yours, choose the colder zone. It will ensure that you get the right size boiler for your home to meet demand during the coldest weather of the year.

What Size Boiler Do I Need for My Home?

There’s a rule of thumb that says take the cubic feet of space and multiply by 4.

For example, a 2,000 square foot home with 8-foot ceilings has 16,000 cubic feet of space. Multiplying times 4 gives you 64,000 BTU, and that is certainly in the range of boiler size for most areas.

That’s an OK rule for homes in moderate climates, but it doesn’t apply everywhere. The calculator above and this size chart are more reliable as guides to sizing a residential boiler.

What Size Boiler Do I Need For My Home

House SizeBoiler Size
(Hot Climate)
Boiler Size
(Moderate  Climate)
Boiler Size
(Cold  Climate)
1,000 square feet18,000 – 30,000 Btu28,000 – 40,000 Btu50,000 – 60,000 Btu
1,300 square feet23,500 – 39,000 Btu36,500 – 52,000 Btu65,000 – 78,000 Btu
1,500 square feet27,000 – 45,000 Btu42,000 – 60,000 Btu75,000 – 90,000 Btu
1,600 square feet28,500 – 48,000 Btu44,500 – 64,000 Btu80,000 – 96,000 Btu
1,800 square feet32,500 – 54,000 Btu50,500 – 72,000 Btu90,000 – 108,000 Btu
2,000 square feet36,000 – 60,000 Btu56,000 – 80,000 Btu100,000 – 120,000 Btu
2,400 square feet43,000 – 72,000 Btu67,000 – 96,000 Btu120,000 – 144,000 Btu
3,000 square feet54,000 – 90,000 Btu84,000 – 120,000 Btu150,000 – 180,000 Btu
3,400 square feet61,000 – 102,000 Btu95,000 – 136,000 Btu170,000 – 204,000 Btu
3,700 square feet66,500 – 111,000 Btu103,500 – 148,000 Btu185,000 – 222,000 Btu

What size boiler do I need for 2000 square feet?

A boiler with 29,000 to 145,000 BTU capacity. The colder your climate, the larger the boiler needs to be. If your home is older with poor insulation or your climate is cloudy, then choose a boiler higher on the capacity range.

Tips for using the boiler size chart:

1). There is a range of boiler sizes for each size home. The colder your region and/or the larger your family, the larger the boiler should be. If your home has older, drafty windows and doors, choose a unit higher on the range too.

2). Also, most boiler series start at between 40,000 and 80,000 BTU. So, for small homes and/or homes in warm climates, the minimum size boiler for your home might not be available. Again, it is OK to use a boiler rated for more square feet than you need – as long as it isn’t much too large.

3). If choosing a combi boiler for heat and domestic hot water, select a unit on the higher end of the BTU spectrum. And always see the manufacturer’s recommendations for finding the right size model for your specific use. 

Boiler Sizes

Most brands, like Weil-McLain, Bosch, Utica, Navien, Slant Fin, Peerless, Crown and other top residential boiler brands manufacture a range of sizes from around 40,000 BTU to well over 200,000 BTU.

So the key is to purchase one large enough for your hot water demands without being too large and wasting energy.


What happens if my boiler is too big?

If your boiler is too big, you will be using more fuel, whether gas or electricity, than you would use if the boiler were properly sized. But if the system thermostat works properly, you won’t have to worry about your home or water being overheated. The system will regulate temperature as necessary.

The waste of energy is worse with electric boilers. However, the energy waste isn’t large, and it is better to have a boiler that’s a little too large than one that is too small.

Do electric boilers use a lot of electricity?

Yes, electric boilers for use in homes use up to 36kW of electricity. As a result, on average, electric boilers are more expensive to operate than gas boilers. The prices of electricity, natural gas and propane all vary across the country.

When you understand the energy price comparison where you live, you’ll have the information needed to decide which type, electric or gas, is most cost-effective for your purposes. 

Written by

Rene has worked 10 years in the HVAC field and now is the Senior Comfort Specialist for PICKHVAC. He holds an HVAC associate degree and EPA & R-410A Certifications. Protection Status