Buyer's guide

Cold-climate heat pumps: what actually matters

'Works down to -13°F' and 'still produces useful heat at -13°F' are different claims. Here is how to tell which one you are being sold.

The claim and the reality

Nearly every heat pump sold today advertises a low-temperature rating. The number is usually real. What it means is usually misunderstood.

"Operates to -13°F" means the compressor will still run at -13°F. It says nothing about how much heat it produces there. A unit can technically operate at -13°F while delivering 45% of its rated capacity, which means your backup heat is carrying more than half the load on the coldest night of the year — at roughly a third of the efficiency you were sold.

The specification that answers the real question is capacity retained at low temperature, expressed as a percentage of the 47°F rating. We publish it for every heat pump in our database, and where a source publishes only raw capacity figures we derive it and say so.

Why AHRI ratings are not enough

The AHRI Directory is the legal system of record for HVAC performance in the United States, and for cooling it is authoritative. For cold-weather heating it has a structural gap: the standard test procedure does not include test points below 17°F.

That is the entire reason NEEP's Cold Climate Air-Source Heat Pump list exists. It publishes capacity and COP at 47°F, 17°F and 5°F for every listed product. A manufacturer choosing to list a product there is choosing to be measured at a temperature where weak products look weak. That willingness is itself a signal, which is why presence on the list is a field in our database rather than a footnote.

Reading a capacity table

If you want to check a specific model yourself, ask the contractor for the manufacturer's extended capacity table — sometimes called performance data or engineering data. Not the brochure. The table lists heating capacity at a grid of outdoor temperatures and indoor conditions.

Find the row for your climate zone's winter design temperature. Compare the capacity there against your house's design heat load. If capacity is below load, the difference is backup heat, and you can calculate roughly what that costs before you sign anything.

Two things to watch for in these tables:

Maximum vs rated capacity. Variable-speed units publish both. Maximum capacity at low temperature is achieved by running the compressor hard, which drops efficiency — the COP at maximum output is lower than at rated output. Both numbers are honest; make sure you are comparing like with like across products.

Defrost. Published capacity figures are typically steady-state and do not account for defrost cycles, during which the unit is not heating your house and may be actively cooling it. In humid climates near freezing, defrost is frequent. This is one reason heat pumps often perform better in a dry cold than a damp one at the same temperature.

Sizing in a cold climate is a genuine trade-off

In a cooling-dominated climate you size for the cooling load and heating comes along for the ride. In a heating-dominated climate the two loads diverge, and you have to choose.

Size to the full heating load and the system will be badly oversized for cooling — short cycling, poor dehumidification, and in a humid summer a house that feels clammy.

Size to the cooling load and you will need meaningful backup heat on the coldest days.

Variable-speed equipment narrows this trade-off considerably, because a system can be sized nearer the heating load and still turn down far enough to cool sensibly. This is the strongest practical argument for inverter equipment in a cold climate, and it is more important than the efficiency rating.

The alternative is dual fuel: size the heat pump to the cooling load, let an existing furnace handle the coldest nights, and set the switchover point where the fuels cross on cost. In a cold-climate house with existing natural gas, this is frequently the lowest total-cost answer available and it is rarely what gets proposed.

Backup heat is a design decision, not an afterthought

Every cold-climate heat pump installation needs a backup plan. Your options:

Electric resistance strip heat. Cheap to install, expensive to run, and it works. The risk is a control strategy that brings strips on too eagerly — some thermostats energise resistance heat during ordinary recovery from a setback, which can quietly double your winter bill. Ask specifically how strip heat is staged and locked out.

Existing fossil furnace (dual fuel). The most economical option if you already have the furnace and the fuel. Requires a control that switches at the right outdoor temperature.

Nothing. Viable with a properly sized cold-climate unit in zone 5, marginal in zone 6, and not advisable in zone 7 or colder. A heat pump with no backup in a genuinely cold climate means a cold house if anything fails on the worst night of the year.

A note on ground-source

Ground-source (geothermal) heat pumps sidestep this entire problem, because ground temperature is stable regardless of air temperature. Capacity does not collapse in January.

The reason we do not lead with them: installed cost is typically two to three times an air-source system, and the Section 25D credit that covered 30% of that cost expired at the end of 2025. In climate zone 7 and colder, or on a property where ground loop installation is straightforward, they are still worth quoting. Elsewhere, the arithmetic got considerably harder in 2026.

---

Equipment in this category