Most homes need a heat pump between 1.5 and 5 tons (18,000 to 60,000 BTU per hour). As a starting point, plan on roughly 1 ton for every 500 to 600 square feet, depending on climate. In mild and warm climates, size the heat pump for your cooling load; in cold climates, the heating load on the coldest days usually decides the size and whether you need a cold-climate model or backup heat.
Use the estimator below for a quick ballpark, then read on to understand what changes the answer.
Heat pump size estimator
Rough estimate for comparison only. A Manual J load calculation by a licensed contractor is the only reliable way to size a heat pump.
Heat pump size chart by square footage
| Home size (sq ft) | Hot or warm climate | Mixed climate | Cold climate |
|---|---|---|---|
| 800 to 1,200 | 2 tons | 1.5 to 2 tons | 1.5 to 2 tons + check heating capacity |
| 1,200 to 1,600 | 2.5 to 3 tons | 2 to 2.5 tons | 2 to 3 tons (cold-climate model) |
| 1,600 to 2,000 | 3 to 3.5 tons | 3 tons | 3 to 3.5 tons (cold-climate model) |
| 2,000 to 2,500 | 4 tons | 3.5 to 4 tons | 4 tons (cold-climate) + backup heat |
| 2,500 to 3,000 | 5 tons | 4 to 5 tons | 5 tons or two systems + backup heat |
Assumes average insulation and 8-foot ceilings. For comparison only.
Cooling load vs. heating load
A heat pump does two jobs, and they rarely need exactly the same capacity:
- Cooling load is driven by sun, windows, insulation, occupants and humidity. It’s usually the bigger number in the South.
- Heating load is driven by how cold your coldest days get and how fast your home loses heat. It’s usually the bigger number in the North.
The problem: a heat pump’s heating capacity drops as it gets colder outside, exactly when your home needs the most heat. A unit rated at 36,000 BTU may deliver only 60 to 80% of that at 5°F, unless it’s a cold-climate model designed to hold capacity.
In mild and warm climates: size for cooling. Oversizing for heating would make the system short cycle in summer and leave the house humid.
In cold climates: choose a cold-climate heat pump (many are listed by the Northeast Energy Efficiency Partnerships, NEEP) and check its heating output at 5°F against your heating load. Cover any gap with electric backup strips or a gas furnace in a dual-fuel setup. Variable-speed heat pumps can be sized somewhat larger for heating because they slow down in summer instead of short cycling.
What a Manual J calculation includes
Contractors should size a heat pump with an ACCA Manual J load calculation, then choose equipment with Manual S. Manual J accounts for:
- Square footage, ceiling height and floor plan.
- Insulation in walls, attic and floors.
- Window area, type and orientation.
- Air leakage.
- Local design temperatures for summer and winter.
- Occupants and internal heat sources.
If a contractor sizes your heat pump only by the size of your old AC or furnace, ask for a load calculation. Old equipment is often oversized, and insulation or window upgrades may mean you need less capacity now.
Signs your heat pump is the wrong size
Too big:
- Short cycling: on and off every few minutes.
- Clammy, humid air in summer.
- Uneven temperatures between rooms.
Too small:
- Runs constantly on hot or cold days and can’t reach the setpoint.
- Backup or auxiliary heat runs often in moderate winter weather.
- High electric bills in winter.
How to read a heat pump’s size
Like air conditioners, the outdoor unit’s model number usually includes the nominal capacity in thousands of BTU: 24 = 2 tons, 36 = 3 tons, 48 = 4 tons, 60 = 5 tons. See the full decoding table in our AC size chart. For heating performance, look at the manufacturer’s extended performance data or the AHRI certificate, which lists capacity at 47°F and 17°F (and 5°F for cold-climate models).
Frequently asked questions
What size heat pump do I need for 2,000 square feet?
Typically 3 to 4 tons, depending on climate and insulation. In cold climates, confirm the unit’s heating capacity at low temperatures matches your heating load.
Is it better to oversize a heat pump?
Single-stage heat pumps shouldn’t be oversized; they’ll short cycle and leave the house humid in summer. Variable-speed models tolerate some oversizing better, which can help in cold climates.
Do I need backup heat with a heat pump?
In mild climates, often not. In cold climates, most homes have electric backup strips or keep a gas furnace for the coldest days.
Is a heat pump cheaper to run than a furnace?
It depends on your energy prices and climate. See our heat pump vs. furnace comparison for the math.
Disclaimer: this estimator and chart are for general information only. Have a licensed HVAC contractor perform a Manual J load calculation before buying a heat pump.