Find the right heat pump size in tons, BTU/h or kW. The calculator works out the home's design heat loss, then sizes the heat pump using how much capacity it really keeps in cold weather, and shows the balance point, any backup heat needed, and mini-split head sizes room by room.
Preliminary sizing. Confirm with a room-by-room load calculation (ACCA Manual J or EN 12831) and the manufacturer's capacity tables before buying equipment.
A heat pump should be sized to the heat loss of the house at the local design temperature, not to the floor area alone. Two homes of the same size can need very different heat pumps: one well insulated in a mild climate, the other older and leaky in a cold one. The second step is just as important: an air-source heat pump loses capacity as it gets colder outside, so a unit rated at 3 tons at 47 °F may deliver only 2 tons on the coldest night.
This calculator handles both steps. It works out the heat loss, then finds the smallest standard size whose cold-weather capacity meets it, or meets it down to the balance point you choose.
Heat loss and suggested size for an average insulated house with 8 ft ceilings, 70 °F indoors and a cold-climate heat pump covering the full load at the design temperature. Use it as a starting point only.
| House size | Mild 32 °F (0 °C) | Cold 14 °F (−10 °C) | Very cold 3 °F (−16 °C) | Severe −10 °F (−23 °C) |
|---|---|---|---|---|
| 1,000 sq ft (93 m²) | 10,000 BTU/h 1 ton | 14,800 BTU/h 1.5 ton | 17,700 BTU/h 2 ton | 21,100 BTU/h 2.5 ton |
| 1,500 sq ft (139 m²) | 15,100 BTU/h 1.5 ton | 22,200 BTU/h 2 ton | 26,500 BTU/h 3 ton | 31,700 BTU/h 4 ton |
| 2,000 sq ft (186 m²) | 20,100 BTU/h 2 ton | 29,600 BTU/h 3 ton | 35,400 BTU/h 4 ton | 42,300 BTU/h 5 ton |
| 2,500 sq ft (232 m²) | 25,100 BTU/h 2.5 ton | 37,000 BTU/h 3.5 ton | 44,200 BTU/h 5 ton | 52,800 BTU/h two units |
| 3,000 sq ft (279 m²) | 30,100 BTU/h 3 ton | 44,400 BTU/h 4 ton | 53,100 BTU/h two units | 63,400 BTU/h two units |
A newer, tighter house needs roughly a third less; an older, leaky one roughly half as much again. A standard heat pump in the colder columns needs either a larger size or backup heat.
| Type | At 17 °F (−8 °C) | At 5 °F (−15 °C) | Typical cut-out |
|---|---|---|---|
| Standard air-source (single-stage) | ~65% | ~50% | −4 °F (−20 °C) |
| Variable-speed air-source | ~80% | ~65% | −13 °F (−25 °C) |
| Cold-climate air-source | ~95% | ~85% | −22 °F (−30 °C) |
| Ground-source (geothermal) | ~100% | ~100% | none |
Percentages of rated capacity at 47 °F (8 °C). These are representative values; individual models vary widely, so use the manufacturer's extended data for the model you are considering.
Above the balance point the heat pump has more capacity than the house needs and cycles or modulates down. Below it, something else has to make up the difference: electric resistance strips, a furnace in a dual-fuel system, or a larger heat pump. Sizing to cover the full load at the design temperature gives a balance point at or below it and needs no backup. Sizing to a balance point of around 25–30 °F (−4 to −1 °C) keeps the heat pump smaller and closer to the cooling load, with backup heat for the few coldest hours of the year.
In cold climates the heating load is usually much bigger than the cooling load. A heat pump sized for heating can then be oversized for cooling, which in humid regions means short cycles and poor dehumidification. A variable-speed or cold-climate unit that can turn down handles this well; with a single-stage unit it is often better to size closer to the cooling load and add backup heat. Enter your cooling load to get this check, or estimate it with the BTU AC Sizing Calculator.
With ductless mini-splits each indoor head serves one room, so each needs its own size. Tick "Size mini-split heads room by room", list the rooms and their floor areas, and the tool splits the heat loss across them and picks a standard head size for each (6,000 to 36,000 BTU/h, or 2.0 to 10 kW). Avoid oversizing small bedrooms: the smallest heads already cover most of them.
The default case: a 2,000 sq ft house with 8 ft ceilings and average insulation, 70 °F indoors, in a very cold climate with a 3 °F design temperature.
For a detailed room heat balance use the Room Heat Load Calculator, for running cost the AC Running Cost Calculator, and for unit conversions the TR to kW converter. Wall, roof and window U-values come from the construction details or the energy code.
It depends on insulation and climate more than area. An average insulated 2,000 sq ft house loses about 20,000 BTU/h at 32 °F and about 35,000 BTU/h at 3 °F. With a cold-climate heat pump that is roughly a 2 ton unit in a mild climate and 3.5 to 4 tons in a very cold one.
For heating, a typical insulated house needs about 10 to 25 BTU/h per square foot at the design temperature, more for older houses and cold climates, less for new tight ones. Older rules of thumb of 40 to 60 BTU per square foot usually oversize the equipment.
The outdoor temperature at which the heat pump's capacity exactly equals the house heat loss. Below it the heat pump cannot keep up on its own and backup heat makes up the difference.
In hot climates size for cooling. In cold climates the heating load is larger: either size for heating with a variable-speed or cold-climate unit that can turn down for cooling, or size closer to the cooling load and add backup heat below the balance point.
Yes. An oversized heat pump short-cycles, wears faster, removes less humidity in summer and costs more to buy. Size it to the calculated load at the design temperature rather than adding large safety margins.
Found a number that looks wrong, or a case the tool does not cover? Say so here — corrections are welcome and get answered.
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