Cold Climate Heat Pumps
Capacity at 5°F, balance points, and when a dual-fuel setup wins.
11 min
Heat pump sizing calculator
A heat pump loses capacity exactly as the house needs more. This finds where the two curves cross — the balance point — and how much electric heat is left to cover below it.
Pre-filled with a 60,000 BTU/h load, a 10 °F design temperature and a 3-ton heat pump.
BTU/h
°F
°F
BTU/h
From the AHRI certificate, not the nominal tonnage.
BTU/h
38°F
Balance point
| Outdoor | Heat pump capacity | House load | Gap |
|---|---|---|---|
| 62 °F | 42,000 | 8,000 | covered |
| 47 °F | 36,000 | 23,000 | covered |
| 35 °F | 31,200 | 35,000 | −3,800 |
| 25 °F | 27,200 | 45,000 | −17,800 |
| 17 °F | 24,000 | 53,000 | −29,000 |
| 10 °F | 21,200 | 60,000 | −38,800 |
The balance point is the whole design
Two lines. The house's heat loss rises as it gets colder outside — straight, from zero at about 62 °F to the full design load at the winter design temperature. The heat pump's capacity falls as it gets colder, because there is less heat outside to move. The temperature where they cross is the balance point. Above it the heat pump covers the house alone; below it something else makes up the difference.
Everything people argue about with heat pumps — running cost, comfort, whether they "work in the cold" — is really an argument about where that crossing sits and what covers the gap underneath.
Use rated capacity, not tonnage
A "3-ton" heat pump is a cooling label. Its heating capacity at 47 °F might be 36,000 BTU/h and at 17 °F only 24,000 — or, on a good cold-climate inverter unit, 34,000. The nominal number tells you nothing about the second figure, and the second figure is the one that decides your winter. Take both from the AHRI certificate for the exact indoor/outdoor combination being quoted.
Match the pair, not the box
Capacity is certified for a specific outdoor unit paired with a specific coil or air handler. Swapping the indoor half changes the rating. If the quote does not name an AHRI reference number, ask for it before you sign.
Reading the supplemental gap
The panel prints the shortfall at design temperature in BTU/h and in kilowatts of electric resistance heat. Divide BTU/h by 3,412 to get kW. A 12,000 BTU/h gap is 3.5 kW — one small strip. A 30,000 BTU/h gap is nearly 9 kW, which is a serious electrical load and often the real reason a heat pump retrofit needs a service upgrade.
If the gap is large and the electric service is tight, a dual-fuel arrangement — heat pump above the balance point, gas furnace below it — avoids the panel work entirely. The heat pump against furnace comparison works through when that pays.
Sizing to heating or to cooling
In a cold climate the heating load is the bigger of the two, and sizing a single-stage heat pump to cover it means an oversized air conditioner in July. Variable-capacity equipment solves that — it can modulate down to a third of its capacity — which is why cold-climate heat pumps are almost all inverter-driven. With single-stage equipment, size to the cooling load and accept a higher balance point.
Federal minimums for split-system heat pumps are 14.3 SEER2 and 7.5 HSPF2; single-package units sit at 13.4 SEER2 and 6.7 HSPF2.
Sources: 10 CFR 430.32(c)(5)(ii) (read 2026-09-04)
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