What Size Heat Pump Do I Need? Heat Pump Size Calculator

Sizing a heat pump seems like a daunting task. How do I calculate what size heat pump do I need? How many BTU heat pump do I need? This is usually an estimate that you need an HVAC expert for.

We are going to simplify how to calculate what size heat pump do you need. That will enable everybody to roughly estimate the size of the heat pump (be it a mini-split heat pump or ground-source heat pump). We will do that in 3 key steps:

  1. First, we’ll look at how HVAC experts size heat pumps (using 8 factors from Manual J; the method was established by Air Conditioning Contractors of America).
  2. Then we’ll simplify these 8 factors with a useful rule of thumb (boiling down 8 complex rules into 1 simple general rule of thumb so that everybody can roughly estimate how big a heat pump should they get). Based on that, we designed the Heat Pump Size Calculator (check further below; you just input square footage and ceiling height, and it will give you roughly BTU you need). We also included a table of how big your mini-split heat pump should be given certain square footage.
  3. To demonstrate how Heat Pump Size Calculator works, we’ll solve 2 examples; ie. calculating what size heat pumps do you need for a 2,500 square foot house.

In the end, you should be able to roughly estimate (and calculate) how big a mini-split heat pump or how big a ground-source heat pump you need for your house.

Note: Do keep in mind that these are only rough estimations that can help you get a feeling of what size heat pump you require. An HVAC expert is required on-site to map out your home, determine heating/cooling needs, and so on for a specific situation you have.

Let’s look at how HVAC experts size a heat pump:

How HVAC Experts Calculate Heat Pump Size (Using Manual J)

Every HVAC expert calculates what size heat pump you need using the same set of principles. When you need heat pump sizing, they all know to look at the Manual J (the alpha and omega book of HVAC sizing) and follow the 8 rules.

These 8 rules include all the main and secondary factors when it comes to sizing any heat pump. They work both for sizing air-source heat pumps (these are mini-split heat pumps) and for sizing ground-source heat pumps.

Here are the 8 rules or factors from Manual J that HVAC experts should follow when sizing a heat pump:

  1. Determine the local climate (+ how many days a year you need heating/cooling). Obviously, if you live in Chicago, you will need a bigger heat pump than if you live in Miami, Florida. In general, colder climates require higher heating output (measured in BTUs or kW).
  2. Total square footage; one of the most important determining factors for sizing a heat pump. Consider the room distribution and general home’s layout as well.
  3. Windows; how many they are, where are they located?
  4. Occurrences of air infiltration; where it is and air infiltration quantification.
  5. Insulation quality; how well insulated is the house, does it meet the region’s efficiency rating?
  6. People; how many people live in the house?
  7. Temperature preferences; what is the ideal temperature of the home for homeowners?
  8. Heat generating appliances; which appliances generate additional heat (oven, fridge, washing machine, etc.)? Sum all of them up and quantify the overall effect on the indoor temperature.

Now, it’s rather complex to determine the effect of all of these factors. These 8 rules were meticulously put together by Air Conditioning Contractors of America and it’s a standard part of Manual J.

Don’t be taken aback by the complexity of everything you need to check to size a heat pump; even HVAC experts who have been in the field for 10+ years use certain simplifications.

Let’s boil these 8 factors down into 1 simple rule of thumb:

How To Approach Heat Pump Sizing On Your Own? (1 Rule Of Thumb)

Some of the factors in Manual J cancel each other out. Example: You can have a badly insulated home but don’t have many windows, and have several 1,000W+ home appliances (oven, washing machine, etc.).

The key determinant of how big a heat pump you need is how big your house is. The bigger the house, the bigger the heat pump you need, right?

Considering all the factors, we can roughly boil them down into a single rule of thumb. This rule of thumb comes very useful when you want to adequately determine the size of the heat pump you need.

Here’s the 1 rule of thumb:

30 BTU of heating output per 1 sq ft of living space.

This heat pump sizing rule is fairly simple to use. It roughly incorporates the averages from the rules found in Manual J. This rule is akin to the EPA’s rule of thumb for sizing air conditioners and it also relates to the heating BTU calculator.

For every sq ft of living space, you need about 30 BTU of heating output. That means, for example, that for a 1,000 sq ft home, you would require a 30,000 BTU heat pump (that’s a 2.5-ton heat pump).

We can use this simple rule to create the Heat Pump Size Calculator:

Heat Pump Size Calculator (Just Input Square Footage)

Another key parameter is the ceiling height. 30 BTU per sq ft rule of thumb is for standard 8 ft high ceiling. If you have higher ceilings, you will need a more powerful heat pump, and vice versa. Here is the calculator:

0.00 BTU

Heat Pump Size (Estimate)

 

Using this calculator, everybody can roughly estimate what size heat pump they need. This is primarily a mini-split heat pump size calculator but can be used to roughly estimate the size of ground-source or even water-source heat pumps.

The heat pump size calculator outputs the resulting size of a heat pump in BTUs (British Thermal Units). You can simply convert that into:

  • Tons (in the US, the capacity of heat pumps is usually measured in tons). Use 12,000 BTU = 1 ton conversion, or make use of the BTU to tons converter here.
  • kilowatts or kW (in Europe, Asia, and rest of the world, the capacity of heat pumps is usually expressed in kW). Use 3412 BTU = 1 kW conversion, or make use of the BTU to kW converter here.

Note – how to make the estimate even more precise: If you live in the cold north (Canada, Illinois, Minnesota), it makes sense to add up to 40% to the total output heat pump capacity calculated by the Heat Pump Size Calculator. If you live in the hot south (Florida, Texas, South California), you can reduce the total output heat pump capacity BTUs by as much as 30%.

Using the calculator, we can create a table that specifies how big a heat pump you need depending on how big your house is (ie. square footage):

Heat Pump Sizing Chart By Square Footage

Home Size: Heat Pump Size (In BTUs): Heat Pump Size (In Tons):
300 sq ft 9,000 BTU 0.75 tons
500 sq ft 15,000 BTU 1.25 tons
750 sq ft 22,500 BTU 1.88 tons
1,000 sq ft 30,000 BTU 2.5 tons
1,500 sq ft 45,000 BTU 3.75 tons
2,000 sq ft 60,000 BTU 5.0 tons
2,500 sq ft 75,000 BTU 6.25 tons
3,000 sq ft 90,000 BTU 7.5 tons

You can see for the heat pump size table that, for example, a 2,000 sq ft house requires around 60,000 BTU or a 5-ton heat pump.

Let’s solve two examples to illustrate how you can calculate what size heat pump you need manually and via the calculator:

What Size Heat Pump Do I Need For A 2,500 Square Foot House? (Example 1)

Let’s say you have a bigger 2,500 sq ft home and you want to buy a heat pump for it. How do you adequately pinpoint how big a heat pump you need?

Well, you should call an HVAC expert, and he or she will use the 8 factors in Manual J to calculate the required size of the heat pump. For you to get a feeling of how many BTU heat pump you should be considering, you can use the simple 30 BTU per 1 sq ft rule to estimate the size of the heat pump for a 2,500 sq ft home.

Let’s do some manual calculating:

For 1 sq ft, you would need 30 BTU of heating/cooling output.

How many ton heat pump (or BTUs) you need for 2,500 sq ft?

Heat Pump Size (2,500 sq ft) = 2,500 sq ft * 30 BTU per sq ft = 75,000 BTU

You would need about 75,000 BTUs. If you convert that into tons, that’s a 6.25-ton heat pump. If you convert that into kW, that’s a 22 kW heat pump.

In short, for a 2,500 sq ft home, you would require a 6.25-ton heat pump.

Let’s see if the Heat Pump Size Calculator also gives us the 75,000 BTU result for a 2,500 sq ft home:

What Size Heat Pump Do I Need For A 2500 Square Foot House

The calculator confirms that our manual calculation was correct.

What Size Heat Pump Do I Need For A 1,500 Square Foot House? (Example 2)

In this example, we have a 1,500 sq ft home and would like to buy a mini-split heat pump for it. Obviously, the first question is what size mini-split heat pump do you need? Once you determine that, you can check out our article about the best mini-split heat pumps currently on the market here.

An HVAC expert on-site will determine the size of the mini-split heat pump exactly but we can estimate what the result will be by applying the 30 BTU per sq ft rule of thumb and manually calculating what size heat pump you need for a 1,500 sq ft home.

Here’s the calculation:

Mini-Split Heat Pump Size (1,500 sq ft) = 1,500 sq ft * 30 BTU per sq ft = 45,000 BTU

For a 1,500 sq ft home, you would need about 45,000 BTU heat pump. Let’s convert that to tons and kWs; that’s 3.75 tons (about 4 tons) and about 13 kW.

In short, you would need about a 4-ton mini-split heat pump for a 1,500 sq ft home.

We can confirm this manual calculation using the mini-split heat pump sizing calculator:

What Size Heat Pump Do I Need For A 1500 Square Foot House

As you can see, the heat pump BTU calculator produces the same result: 45,000 BTU.

Final Words

Always remember that for adequate sizing, you would need an HVAC expert that does the on-site sizing. The heat sizing here can serve as a rough reference.

If you are in the market for a heat pump, you can contact vetted HVAC experts in your area using this form here. You will get up to 4 free quotes on heat pumps and they will help you out with proper heat pump sizing as well.

Hope all of this helps a bit.

8 thoughts on “What Size Heat Pump Do I Need? Heat Pump Size Calculator”

  1. I have a Daikin contractor sizing my home of 1400+ sq. ft. requiring a 12,000 BTU mini ducted heat pump. I am concerned with the suggested size. The contractor after a second house visit has suggested a larger size heat pump at 15,000 BTU. My home is a standard ranch style home with three bedrooms, 1.5 bathrooms din/kit. and liv. . The layout is fairly standard my climate is the same as any of your New England states (Nova Scotia Canada). My contractor is a certified Daikin installer with an exceptional reputation. Who is right and who is wrong ?

    Reply
    • Hello Harold, a mini-split heat pump is usually used as an auxiliary heating source and primary air conditioning source. Do you have a primary heating source? Something like a furnace or an existing ducted HVAC system? Based on the heating output of that heating source and the size of your home, the Daikin installer will try to choose the most optimum heat pump size. The Daikin installer’s first suggestion was 12,000 BTU and then he/she reevaluated the sizing and came up with 15,000 BTU? The size upgrade for such a home makes more sense. It would be best to trust a hands-on installer who can evaluate the heating/cooling needs on-site.

      Reply
  2. I live in a 2,400 square foot two-story home with an existing gas furnace (7 years old) and air conditioning unit (21 years old). I’m interested in exploring whether it’s worth it to replace the A/C with a 75,000 BTU heat pump (according to your calculator) which would provide air conditioning as well as heat up to a certain point at which the gas furnace would take over in more extreme temperatures. I live in the Toronto, Canada area which would be similar to Chicago. I’ve already installed an electric heat pump water heater and I’m very happy with the savings so far. I’m also arranging for a Home Depot HVAC representative to estimate the cost. Also, which brand would you recommend for the best efficiency? Thanks

    Reply
    • Hello Phil, you have the right outlook. The 21-year-old AC is probably not efficient by today’s standards. Quite possibly, it has a SEER rating (cooling) below 14 and an HSPF rating (heating) below 8. The new AC will probably have a SEER rating of 20 or more and an HSPF rating of about 10. That will likely save you about 40% of AC and heating costs. As far as the brand is concerned, it might be best to ask a Home Depot representative. Mitsubishi and Gree make great heat pumps, for example, with a 20+ SEER rating (very energy efficient). The best DIY heat pumps are made by MrCool, for example. They have a 10 HSPF rating and 20+ SEER rating; you can read more about MrCool DIY heat pumps here. Hope this helps a bit.

      Reply
  3. Hi, I am wondering if air source heat pumps are a possibility in a commercial office setting? The office I work in is approximately 1514m2 (16,297ft2). Is a large heat pump an option in this sized building? Or would multiple units be required? Any info would be great! Thanks

    Reply
    • Hello Fergus, that’s quite a lot of office space. Depending on how well the whole office is insulated, you would require about 500,000 BTU of heating output. Of course, you can use a bunch of air source heat pumps to generate that heat. You can check our article about some of the best air source heat pumps for cold weather here. As you can see, most of these units are 2-ton units; they generate 24,000 BTU of heating output. For a 1,514m2 (16,297ft2) office space, you would about 20 of these. It’s possible; the real question is if the central heating system wouldn’t be a better solution. Hope this insight helps.

      Reply
  4. I am planning to use concrete filled ICF forms that have R22 rated and have 2400 sq ft main floor and 1200 sq ft daylight basement (one side only), with 9.5 ft ceilings, in zone 4. Will this reduce my needed BTU calculations?

    Reply
    • Hello Roger, the single most important factor that decreases the required BTU load is good insulation. The better insulation, the lower the BTU requirements. We have talked about the R-value of insulating materials here. If you check the concrete R-value, it’s quite low, however. It is rather difficult to theoretically determine what an effect the concrete-filled ICF forms will have, to be honest.

      Reply

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