Heat pump size chart
Recommended ducted heat pump size and electric backup heat for an all-electric home with 8 ft ceilings and average insulation. Cold and very cold zones assume a cold-climate heat pump.
| Home size | Hot IECC 1–2 | Warm IECC 3 | Mixed IECC 4 | Cold IECC 5 | Very cold IECC 6–7 |
|---|---|---|---|---|---|
| 1,000 sq ft | 2 t · 0 kW | 2.5 t · 5 kW | 2 t · 5 kW | 2.5 t · 5 kW | 2.5 t · 8 kW |
| 1,500 sq ft | 3.5 t · 0 kW | 3.5 t · 5 kW | 3 t · 8 kW | 3.5 t · 5 kW | 3.5 t · 10 kW |
| 2,000 sq ft | 4.5 t · 0 kW | 4.5 t · 5 kW | 4 t · 8 kW | 4 t · 10 kW | 4 t · 15 kW |
| 2,500 sq ft | 2 systems | 2 systems | 5 t · 10 kW | 5 t · 15 kW | 5 t · 20 kW |
t = tons of nominal capacity (1 ton = 12,000 BTU/h). kW = electric backup heat strips installed in the air handler.
Why heat pumps are sized differently
An air conditioner only has to handle the hottest afternoon. A heat pump has to handle that and the coldest night. Its heating output is rated at 47 °F outdoors, and it falls as the temperature drops, because there is less heat in the outside air to move indoors.
Contractors size heat pumps for the design temperature: the outdoor temperature that is colder than 99% of the hours in a year at your location. The calculator uses these typical values:
| Climate zone | Design temp | Heat loss BTU/sq ft | Standard HP output | Cold-climate HP output |
|---|---|---|---|---|
| Hot · IECC 1–2 | 35 °F | 18 | 85% | 95% |
| Warm · IECC 3 | 25 °F | 22 | 70% | 90% |
| Mixed · IECC 4 | 15 °F | 26 | 60% | 85% |
| Cold · IECC 5 | 5 °F | 32 | 50% | 75% |
| Very cold · IECC 6–7 | −10 °F | 38 | 35% | 65% |
Output is shown as a share of the unit's rated capacity at 47 °F. Heat loss here is the actual heat a home loses at the design temperature, which is lower than the rule-of-thumb figures used to size furnaces, because those include a safety margin.
Standard vs cold-climate heat pumps
Cold-climate heat pumps use variable-speed compressors and vapor injection to keep most of their output well below freezing. Many keep 70% or more of their rated capacity at 5 °F. The Northeast Energy Efficiency Partnerships (NEEP) keeps a public list of models that meet its cold-climate specification.
- Hot and warm climates: a standard heat pump is usually enough. Size it for cooling and let a small strip heater cover rare cold snaps.
- Mixed climates: either type works. A cold-climate model needs less backup heat and runs more efficiently in winter.
- Cold and very cold climates: choose a cold-climate model, or pair a standard heat pump with a gas furnace.
How much backup heat you need
Electric resistance strips in the air handler fill the gap between what the heat pump delivers and what the house loses on the coldest night. They are sold in 5, 8, 10, 15 and 20 kW sizes. Each kW adds 3,412 BTU/h of heat but uses about three times more electricity per BTU than the heat pump, so the goal is to keep them as small as practical.
Larger strip heaters also need a larger electrical circuit. A 15 kW strip draws about 63 amps at 240 volts, which can trigger a panel upgrade in older homes.
Dual fuel: heat pump with a gas furnace
In a dual-fuel system the heat pump heats the house until the outdoor temperature drops below a set point, usually between 25 and 40 °F, then the gas furnace takes over. The heat pump is sized for cooling, and the furnace is sized for the full heating load. This setup is common in cold climates where gas is cheap and electricity is expensive.
Frequently asked questions
What size heat pump do I need for a 2,000 sq ft house?
Usually 4 to 4.5 tons for an all-electric home with average insulation, plus 5 to 15 kW of backup heat depending on climate. With a gas furnace as backup, the heat pump can be sized for cooling alone, typically 3 to 4.5 tons.
What size heat pump do I need for a 1,500 sq ft house?
About 3 to 3.5 tons in most climates, with 5 to 10 kW of backup heat.
Should a heat pump be the same size as my old AC?
Only in hot and warm climates. In mixed and colder climates the heating load is larger than the cooling load, so the heat pump is often half a ton to a ton bigger than the AC it replaces.
Can a heat pump heat a house below freezing?
Yes. Standard heat pumps keep heating below freezing with reduced output. Cold-climate models can keep most of their capacity at 5 °F and keep running below −10 °F.
Is it bad to oversize a heat pump?
Oversizing for heating can make the system short-cycle and remove too little humidity in summer. Variable-speed heat pumps tolerate some oversizing because they slow down at mild temperatures.
How many kW of backup heat do I need?
Divide the heating shortfall at your design temperature in BTU/h by 3,412. Most homes use 5 to 15 kW; very cold climates with standard heat pumps can need 20 kW or more.
These results are planning estimates. A Manual J heat-loss calculation and the manufacturer's extended performance data at your design temperature should confirm the final size.