How to Measure Heat Pump Efficiency

Heat pumps, even those in different categories, do roughly the same things. However, they may be tuned slightly differently in order to work efficiently in different home makeups, sizings, among other things.

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Heat pumps use different efficiency ratings (COP) and power outputs (BTU/h) as indoor and outdoor temperatures change, among other factors. An inverter unit will be most efficient at the lower end of its output temperature range. Learn more about the different ways to measure heat pump efficiency below.

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In a nutshell: Use SEER2 to see how good a unit is at cooling, HSPF2 for heating, and COP for overall. A higher rating is always better.

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Point-in-Time Ratings

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Coefficient of Performance (COP)

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This measures ratio of heat energy output vs. the energy put into it. Typically in the range of 2-4 which indicates that the heat pump puts out 2-4 times more heat energy than electrical energy it consumes. A resistance electric heat strip or gas heater has a COP of 1.

❗️Manufacturers will often advertise a COP, but watch out! Unless they say the temperature it was measured at, assume it was at ideal (fairly warm) conditions.

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EER

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Energy Efficiency Rating

Measures the cooling energy efficiency at the outdoor temperature of 95°F.

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EER2

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Energy Efficiency Rating — version 2

Like EER but newer, which also specifies an interior temperature of 80°F and humidity of 50% when the measurement is taken. This ensures like-for-like comparisons between models.

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Seasonal Ratings

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SEER2

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Seasonal Energy Efficiency Rating v2

You'll see this measurement a lot when comparing heat pumps for Inflation Reduction Act rebates and incentives. The programs are designed with SEER ratings in mind.

A measurement of how efficiently the heat pump cools over the course of a year. 16-22 are good values. SEER is an outdated version of SEER2. Trane has an article on SEER.

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HSPF2

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Heating Seasonal Performance Factor

A measurement of how efficiently the heat pump heats over the course of a year. A good value is above 8.8 for a large unit, or 12 for a small one.

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HSPF 4-6

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Heating Seasonal Performance Factor — Climate Zones four though six.

A measurement heating based on different climate zones. For example, the New England states are in climate zones five or six, and an HSPF6 rating will be biased to focus on the coldest temperatures. Note that HSPF2 (the second version of HSPF) is the same as HSPF4 (HSPF for climate zone four).

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When shopping for cold-climate heat pumps, I recommend using HSPF2 as a comparison basis. This rating is much more broadly available for different units than climate-zone specific information, and generally a unit which has a higher HSPF2 rating will also have a higher climate zone 6 rating.

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What to expect from a Heat Pump in your Home

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Measuring Output Capacity

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The heating or cooling capacity of a heat pump is measured in tons. A 1-ton heat pump has the equivalent cooling power of one ton of ice in an 1800s-era icebox. Or, if you don’t live in the 1800s, that’s equivalent to 12,000 (12k) BTUs of heat. The right amount of heat for you depends on many factors, such as home size, tightness, amount & quality of insulation, and expected outdoor winter temperatures.

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Outdoor Temperature Ranges

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A heat pump which is not rated for cold weather will quickly lose the ability to heat your home as winter sets in. To compensate for this, many manufacturers offer a specialized “cold weather” product line, which operates at full heat output down to 5°F or lower, before dropping below the rated heating amount. Regardless of what marketing material might have you believe, the technology behind these is not magic: the hardware is sized and tuned a little differently, and the software is written to optimize for heating instead of cooling.

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Watch out for units which advertise low temperature ranges without guarenteeing heat output. One example seen in the chart below is that the Gree 30k compares favorably in terms of raw to the Mitsubish 18k, but at a lower (worse) HSPF2. On Mitsubishi’s scale, the would be rated only at 25-26k.

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Rules of Efficiency

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Some factors will bring up the efficiency of a heat pump. Typically, a smaller unit will be more efficient at heating and have a higher HSPF2. For example, an HSPF2 of 10 is pretty good for a 1.5ton unit (18k BTU), or HSPF 12 is good for a 0.75-ton (9k BTU) unit. The savings are usually not enough to warrant splitting your install into smaller units for that reason alone.