Heat pump size calculator
Enter the floor area, climate zone and how well the house is built. You get the cooling load estimate, the heat pump sizes Manual S allows, and, if you have a heat loss figure from a Manual J or energy audit, how much the heat pump covers on the coldest day and how much backup heat it needs.
Inputs
Result
Every size for your house
Nominal sizes against your cooling load, and, with a heat loss, the heating on the coldest day.
How a heat pump is sized
A heat pump is sized to the house’s cooling load, the same way as an air conditioner, and then checked against the heating load. ACCA Manual S, the industry’s equipment selection standard, lets the heat pump’s cooling capacity go up to 115% of the cooling load where cooling dominates, and up to 125% where heating dominates, so a cold-climate house can take a little more heat pump for winter without short-cycling in summer.
A 2,000 sq ft house of average construction in zone 4 has an estimated cooling load of 36,000 BTU/h, so a 3 ton heat pump (36,000 BTU/h, 100% of the load). In zone 5, where heating dominates, the estimate is 32,000 BTU/h and Manual S allows up to 40,000 BTU/h, so 3 ton is the size: 3.5 ton (42,000 BTU/h) would be over the limit.
Heat pump size chart
Tons by floor area and IECC climate zone, average construction, 8 ft ceilings: the smallest nominal size that meets the estimated cooling load. A tight newer house needs about a quarter less; a leaky older one about a fifth more.
| Floor area | Zone 1 | Zone 2 | Zone 3 | Zone 4 | Zone 5 | Zone 6 | Zone 7 |
|---|---|---|---|---|---|---|---|
| 1,000 sq ft | 2.5 | 2 | 2 | 1.5 | 1.5 | 1.5 | 1.5 |
| 1,200 sq ft | 2.5 | 2.5 | 2 | 2 | 2 | 1.5 | 1.5 |
| 1,500 sq ft | 3.5 | 3 | 2.5 | 2.5 | 2 | 2 | 1.5 |
| 1,800 sq ft | 4 | 3.5 | 3 | 3 | 2.5 | 2.5 | 2 |
| 2,000 sq ft | 5 | 4 | 3.5 | 3 | 3 | 2.5 | 2 |
| 2,200 sq ft | 5 | 5 | 4 | 3.5 | 3 | 3 | 2.5 |
| 2,500 sq ft | >5 | 5 | 5 | 4 | 3.5 | 3 | 2.5 |
| 3,000 sq ft | >5 | >5 | 5 | 5 | 4 | 3.5 | 3 |
Heating: backup heat and balance point
A heat pump loses capacity as it gets colder outside, while the house loses heat faster. Where the two lines cross is the balance point: below it, backup heat (electric strips or a furnace) makes up the difference. ENERGY STAR cold-climate heat pumps must keep at least 70% of their 47°F heating capacity at 5°F; standard models keep less, so read your model’s figure from its data sheet.
Say a zone 5 house has a design heat loss of 45,000 BTU/h at 5°F. A 3 ton cold-climate heat pump keeps 25,200 BTU/h at 5°F, leaving 19,800 BTU/h, or 5.8 kW of backup heat, and its balance point is about 25°F. A 5 ton unit would cut the backup to 0.9 kW but is more than Manual S allows for that cooling load.
We don’t estimate the heat loss from floor area here. The square-foot rules for furnaces include a sizing margin and overstate the real heat loss, which would make the backup heat look far larger than it is. A Manual J calculation or an energy audit gives the real figure.
Questions
What size heat pump do I need for a 2000 sq ft house?
About 3 ton in a mixed climate (zone 4), 4 ton in a hot one (zone 2) and 2.5 ton in a cold one (zone 6), for average construction. In cold zones the heating side decides how much backup heat it needs, so check that with your heat loss. A Manual J calculation gives the real loads.
What size heat pump for a 1500 sq ft house?
About 2.5 ton in zone 4, 3 ton in zone 2 and 2 ton in zone 6, for average construction.
What size heat pump for a 2500 sq ft house?
About 4 ton in zone 4, 5 ton in zone 2 and 3 ton in zone 6, for average construction.
How do I calculate what size heat pump I need?
Size it to the cooling load: floor area times the BTU per square foot for your climate zone, adjusted for construction and ceiling height, divided by 12,000 for tons. ACCA Manual S allows up to 115% of that load, or 125% in heating-dominated climates. Then check the heating side with your heat loss.
Should a heat pump be sized for heating or cooling?
For cooling, with the heating checked. Sizing for the winter load usually oversizes it for summer, so it short-cycles and removes less humidity. Manual S lets you go to 125% of the cooling load in cold climates; beyond that, backup heat or a cold-climate model covers the coldest days.
What is a heat pump balance point?
The outdoor temperature at which the heat pump's output equals the house's heat loss. Below it the heat pump can't keep up alone and backup heat runs. A larger or cold-climate heat pump lowers the balance point.
How much backup heat does a heat pump need?
The heat loss at your design temperature minus what the heat pump delivers then, divided by 3,412 for kW. For a 45,000 BTU/h heat loss at 5°F and a 3 ton cold-climate heat pump, about 5.8 kW.
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