Heat pump sizing — cooling load vs heating load
A heat pump is one machine doing two jobs, and the correct size depends on which load is bigger where you live. In the South, size to the cooling load (like an AC) and heating comes along for free. From the Mid-Atlantic northward, the heating load dominates — this calculator raises the BTU-per-square-foot factor as your climate gets colder, so the recommended tonnage covers most of the winter without leaning constantly on backup heat.
Cold-climate reality check
Standard heat pumps lose capacity as outdoor temperature falls — a nominal 3-ton unit may deliver barely 60% of its rating at 5 °F. Modern cold-climate (hyper-heat) models hold 80–100% of capacity down to -5 °F and keep working to -15 °F or lower. If your area's design temperature is below about 15 °F, pick a cold-climate model and expect the calculator's recommendation to be roughly right; with a standard model you would need to oversize for winter and suffer poor summer dehumidification.
| Home size | Hot South | Mixed | Cold |
|---|---|---|---|
| 1,200 sq ft | 2 tons | 2.5 tons | 3 tons |
| 1,600 sq ft | 2.5–3 tons | 3–3.5 tons | 4 tons |
| 2,000 sq ft | 3.5 tons | 4 tons | 5 tons |
| 2,600 sq ft | 4–4.5 tons | 5 tons | 5 tons + aux |
Frequently asked questions
What size heat pump for a 1,500 sq ft house?
Roughly 2.5 tons in the hot South, 3 to 3.5 tons in mixed climates, and 4 tons (cold-climate model) in genuinely cold regions — assuming average insulation.
Do heat pumps work below freezing?
Yes. Modern cold-climate models deliver full or near-full capacity at 5°F and keep heating to -15°F and below. Standard models lose significant capacity below freezing and rely more on electric backup strips.
Should I size a heat pump for heating or cooling?
Whichever load is larger for your climate — cooling in the South, heating in the North. Oversizing for the smaller load hurts comfort, so cold-climate homes should use variable-speed units that modulate down in summer.
What is HSPF2?
The heating equivalent of SEER: seasonal heating output divided by electricity used, under the newer 2023 test standard. Federal minimum is 7.5; efficient units reach 8.5–10+.