Buyer's guide

How to choose a heat pump

Sizing beats efficiency, capacity at 5°F beats HSPF2, and the contractor matters more than the brand. A practical order of operations.

Start with the thing nobody sells you

The single largest determinant of whether you are happy with your heat pump in five years is not the brand on the box. It is whether the system was sized correctly and commissioned properly. Both of those are contractor decisions, and both are routinely done badly.

An oversized system — which is the overwhelmingly common error — reaches temperature quickly, shuts off, and repeats. Each cycle is inefficient, the house never dehumidifies properly in summer, temperatures swing, and the compressor wears out early. The reason it happens is simple: nobody has ever been sued for installing a system that was too big, and running a proper load calculation takes a few hours that the contractor is not paid for.

So the first question to ask any contractor is: will you perform a Manual J load calculation on my house? Not a rule of thumb, not a "we always put in a 4-ton on a house this size," not matching whatever is there now. If the answer is evasive, that tells you most of what you need to know about how the rest of the job will go.

The estimates on this site — including the design load figure our recommender produces — are planning numbers to help you sanity-check a quote. They are not a substitute for a real load calculation on your actual house.

Then decide the system type, not the model

Most people start by comparing models. That is the last decision, not the first. Work through these in order:

Do you have usable ductwork? If yes, a ducted system is almost always the least disruptive and lowest-cost path. If no, retrofitting ducts into a finished house typically costs $10,000–$20,000 and eats closet and ceiling space — ductless is usually better value, not a compromise.

How cold does it actually get? Not the record low. The 99% winter design temperature — the temperature only about 1% of winter hours fall below. That is the number engineers size to, and it is what determines whether you need cold-climate equipment or are paying for capability you will never use. Our climate zone pages list it for every zone.

What fuel are you on now, and what does it cost you? In much of the country a heat pump is cheaper to run than anything else. In states with expensive electricity and cheap natural gas, it may not be. This depends entirely on your local prices, which is why our recommender computes it from your state's actual energy rates rather than a national average. Run it before you decide.

Do you want to keep a backup heat source? In a cold climate with existing gas, a dual-fuel setup — heat pump for most of the season, gas furnace for the coldest nights — is frequently the lowest total-cost answer. It is also rarely proposed, because it involves two pieces of equipment and a switchover control that the contractor has to understand.

Now the specifications, in order of how much they matter

Capacity retained at 5°F

This is the most important number and the least advertised. Heat pumps lose heating capacity as it gets colder, exactly when you need more of it. A conventional heat pump may retain only 50–60% of its rated capacity at 5°F. The best cold-climate units retain 100%.

The difference is not academic. If your house needs 40,000 BTU/h at design conditions and your heat pump delivers 22,000, the remaining 18,000 comes from electric resistance backup at a third of the efficiency. That is where surprise January electric bills come from.

COP at 5°F

Coefficient of performance at 5°F: units of heat delivered per unit of electricity, at the temperature that matters. A COP of 2.0 means you are still getting twice the heat of resistance heating on a cold night. Below about 1.7, the efficiency advantage over strip heat has largely evaporated.

HSPF2 — useful, but read the fine print

HSPF2 is the headline seasonal heating efficiency number, and it is calculated for DOE Region IV, roughly climate zone 4. If you live somewhere genuinely cold, HSPF2 flatters equipment that performs poorly below freezing, because the rating spends most of its weight at temperatures your winter does not spend much time at.

A unit with an excellent HSPF2 and mediocre 5°F capacity is a mild-climate product wearing a cold-climate marketing badge. Our validation pipeline flags exactly this combination.

SEER2 — matters in proportion to your cooling season

In Phoenix, cooling efficiency dominates your bill and SEER2 is worth paying for — though EER2 at high outdoor temperature is arguably more relevant there, because SEER2 is measured at 82°F and your afternoons are far hotter. In Maine, the difference between SEER2 18 and 21 will show up as a rounding error.

Note also that SEER2 replaced SEER in 2023 and uses a higher external static pressure. SEER2 numbers run roughly 4–5% below the old SEER for identical equipment. Never compare a SEER figure to a SEER2 figure — a "20 SEER" unit from 2021 is not better than a "19 SEER2" unit from 2026.

Variable speed

Variable-speed (inverter) compressors modulate output continuously instead of running flat out or not at all. In practice this is the single biggest comfort upgrade available: steady temperatures instead of swings, quiet operation, and genuine dehumidification because the system runs long and low rather than blasting and stopping.

For most households this is worth more than a couple of points of SEER2. It also requires competent commissioning — a badly set up variable-speed system performs worse than a good single-stage one.

The refrigerant transition

New residential systems now use low-GWP refrigerants — R-454B or R-32 — replacing R-410A. If you are offered discounted R-410A equipment, understand what you are buying: the refrigerant is being phased down, and service costs over the system's life will rise as supply tightens. For a system you expect to keep 15–20 years, the discount is usually not worth it.

What to actually do with a quote

Ask for the AHRI certificate number for the specific indoor/outdoor combination being installed. Efficiency ratings apply to matched pairs, not to the outdoor unit alone, and rebates and code compliance generally require the certificate for the combination. A quote that names only an outdoor unit model is incomplete.

Ask what the backup heat strategy is, and at what outdoor temperature the system switches over. If the contractor cannot answer, they have not thought about your coldest days.

Ask about warranty registration. Several manufacturers require registration within 60–90 days of installation to get the full term. Missing that deadline silently drops you to a much shorter base warranty, and it is the installer's job to do it.

Get three quotes. Installed pricing for the same equipment varies enormously by contractor, and it varies more than the price difference between brands.

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