Heat Pump Sizing Calculator
Enter a ZIP code, square footage and how well the house is insulated. You get an estimated heating and cooling load, the capacity a heat pump needs at your design temperature, and a nominal size to start shopping from. It is an estimate only, not a room-by-room Manual J, and every assumption is listed under the result.
Heat pump sizing calculator
Northeast US (default)Zone 5A · 5°F heating / 88°F cooling design
Estimate only. Not a substitute for a room-by-room Manual J.
Estimated heating load
36,700 BTU/h
31,200 BTU/h – 42,200 BTU/h at 5°F outdoor
Estimated cooling load
24,500 BTU/h
2 tons · 88°F outdoor
Nominal size to shop for
2.5 tons
Capped by cooling limits; supplemental heat needed
Rated heating capacity needed
45,900 BTU/h
at 47°F, assuming 80% retained at 5°F
Supplemental heat: about 12,700 BTU/h on the coldest design hour (electric strip, existing furnace or boiler). Most hours of the winter the heat pump carries the whole load.
Equipment is selected from manufacturer expanded performance data at your design temperature, not from the nameplate tonnage. Nominal tons are a shopping shortcut; the number that matters is capacity at 5°F.
Assumptions behind this estimate
- Climate
- Northeast US (default) (zone 5A)
- Design temperatures
- 5°F heating / 88°F cooling (approx. 99% / 1%)
- Indoor setpoints
- 70°F heating / 75°F cooling
- Insulation level
- average
- Wall / ceiling / window U
- 0.085 / 0.035 / 0.55
- Infiltration
- 0.5 ACH natural
- Window area
- 349 sq ft (15% of wall)
- Occupants
- 3
- Capacity retention
- 80% of 47°F rating at design temp (cold-climate)
Do this room by room in Tradewright
Real equipment matches, a 15-year cost comparison and a signed proposal, all from one visit.
Why square-foot rules mislead
The old shortcut says one ton for every 400 to 600 square feet. That rule has no idea where the house is, how it was built or how much glass faces the afternoon sun. A 2,000 sq ft house in Georgia and the same plan in northern Vermont get the same answer, and a leaky 1950s cape gets the same answer as a tight new build.
Getting it wrong costs real money. Oversized equipment short cycles: it reaches setpoint fast, shuts off and starts again, which wears parts, leaves uneven temperatures and pulls less moisture out of the air in summer. It also costs more to buy and can force bigger ducts or electrical service than the house needs.
For a heat pump the number that matters is not the nameplate tonnage. It is how much heat the unit still delivers at your heating design temperature, which can be well below its 47°F rating. That is why this calculator works out the rated capacity you need from the load at design, then checks it against the cooling limits in ACCA Manual S.
Sources
How the estimate works
Four steps, the same order a load calculation follows. Every number feeds the assumptions list under your result.
Step 1: ZIP to design temperatures
Your ZIP prefix maps to an IECC climate zone and approximate 99% heating and 1% cooling design temperatures. Not sure of the ZIP? Pick a zone instead.
Step 2: Envelope from year and insulation
Year built and insulation level set wall, ceiling, floor and window U-factors, window solar gain and air leakage. Override the year-based guess if you know better.
Step 3: UA × ΔT plus infiltration and gains
Heat loss is each surface's U-factor × area × temperature difference, plus air leakage. Cooling adds solar gain through glass, people, appliances and moisture.
Step 4: Manual S style limits
We divide the heating load by the capacity the unit keeps at design temperature, then cap the size against the cooling load so the unit does not end up badly oversized for summer.
Questions
What size heat pump do I need?
It depends on the heating load at your design temperature, not just square footage. Enter your ZIP, size and insulation above to get an estimated load and a nominal size, then have a contractor confirm it with a room-by-room Manual J and the manufacturer's capacity data at your design temperature.
How do you size a heat pump?
Calculate the heating and cooling loads at the local design temperatures, then pick a unit whose actual capacity at the heating design temperature covers the heating load while staying within Manual S limits for cooling. If it cannot do both, size for cooling limits and plan supplemental heat for the coldest hours.
Is a bigger heat pump better?
No. An oversized heat pump short cycles, controls humidity poorly in summer and costs more to buy. Variable-speed units tolerate some oversizing better, but the goal is still to match the load, not to beat it by a wide margin.
What is the difference between a cold-climate and a standard heat pump?
Cold-climate heat pumps are built to keep much more of their rated capacity at low outdoor temperatures. A standard unit can lose a large share of its heating output by the time it is in the teens. In cold zones that difference decides whether the heat pump carries the house or leans on backup heat.
How many BTU per square foot does a heat pump need?
There is no single number. Heating load per square foot changes with climate, insulation, air leakage and window area, so two homes of the same size can differ by a factor of two or more. The calculator shows BTU per square foot for your inputs as a check, not as a rule.
Do I need backup heat with a heat pump?
Sometimes. If a unit sized within cooling limits cannot cover the heating load at design temperature, the gap is covered by electric strips, an existing furnace or boiler, or a second heat pump. The calculator shows that supplemental amount when it applies.
How accurate is this calculator?
It is a first-pass estimate. It uses a whole-house block load with generalized insulation values and regional design temperatures, so it can be off in either direction. Use it to check a quote or start a conversation, not to order equipment.
What is a Manual J?
Manual J is the ACCA method for calculating heating and cooling loads room by room from the actual walls, windows, insulation, air leakage, orientation and duct location. Most permit offices and many rebate programs expect one for equipment sizing.
Related calculators and guides
Get a room-by-room Manual J and real equipment matches in Tradewright.
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