3 Key Things to Know About Heat Pump Sizing

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If you’re on the prowl for a new heat pump for your HVAC system, you might not know where to turn. There are many heat pumps available on the market, making it difficult to know which models are better or worse. Avoid getting stuck in your decision by using this guide about heat pump sizing.

How to Calculate the Tonnage

Heat pumps come in different sizes, so the first thing you should do is determine which size best fits your home. To do this, you’ll need to know your home’s total square footage. Then, you’ll need to find the tonnage of the heat pump you’re considering.

To determine this, look at the heat pump’s model number. It should have a number divisible by 12 at the beginning or end. Divide this number by 12 to get the unit’s total tonnage. In heating terms, 1 ton is equal to 12,000 Btu/h.

Typically, you should have 1 ton for every 600 to 650 square feet. Here are a few guidelines for choosing a heat pump based on tonnage:

  • 1000-square-foot home = 2-ton unit
  • 1,500-square-foot home = 3-ton unit
  • 2,000-square-foot home = 4-ton unit
  • 2,500-square-foot home = 5-ton unit
  • 3,000-square-foot home = 6-ton unit

Use the Manual J or Manual S Method

Obviously, more goes into heating a home than square footage. That’s where the Manual J and Manual S methods of calculating heat pump sizing come in. Manual J allows you to calculate your home’s total heating load based on many factors, including:

  • Window and floor area
  • Wall area
  • Ceiling area
  • Insulation values
  • Building envelope and air duct leakage
  • Roof surface color
  • Building orientation
  • Occupancy

As you can see, this is far more complicated than the tonnage method, but it’s more accurate for calculating your precise heating load. Manual J is tricky to calculate by hand, but there are several good computer programs available to help you with it.

While Manual J is calculated based on your home’s features, Manual S is based on the features of the heat pump you’re looking at and will determine how well that pump will work in your space. You can also use a computer program to calculate it.

Don’t Choose an Oversized or Undersized Unit

Don’t just choose a bigger unit because you don’t feel like measuring, as bigger units cost more money to run. Finding a system that fits your space precisely will be far more energy-efficient over time. With an oversized system, you’ll have temperature fluctuations and poor humidity control, as the system won’t stay on long enough to filter all the air in the home.

Choosing an undersized unit could be just as detrimental, as it will run constantly to try to heat your space. This nonstop workload will create more wear and tear on the unit, potentially leading to earlier deterioration of the compressor.

Choosing a heat pump doesn’t have to be a nightmare. Use these tips to determine which size is right for your home.



Wife, mother, grandma, blogger, all wrapped into one person, although it does not define her these are roles that are important to her. Entering into their 'empty nest' stage in life, Becky, and her husband Roger are learning to live with their youngest away at school more than not. Becky enjoys way too many TV programs but her favorites are normally criminal based or something to make her laugh. Keep an eye out because 2018 is going to be her year!

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Michele Pineda
Michele Pineda

very informative! I am looking to convert to heat pumps instead of my oil furnace since I cannot stand the forced hot air system I have, my allergies act up terribly. Also my upstairs is not even heated, so this might be an option to get some heat up there as well.

Richard Hicks
Richard Hicks

It is so important to get the right size otherwise the heat pump will run too much or not enough.