Energy Calculators

Heat pump size calculator

Get a first estimate of the heating load and cooling capacity your heat pump needs, before you ask for quotes.

A typical U.S. gas-heated home of 1,614 sq ft needs about 36.6 million Btu of heat a year (EIA RECS 2020, adjusted to 2016–2025 NOAA weather), which works out to a heating load of about 22,829 Btu/h (1.9 tons) at an example design temperature of 5 °F.

Pre-fills typical heating use (EIA RECS 2020) and degree days (NOAA).

Heating
sq ft
million Btu

Estimated from state averages; your bills give a better number (therms used for heating × AFUE ÷ 10).

Contiguous U.S. 10-year average (NOAA).

°F

Example value. Ask your HVAC contractor or building department for your location’s heating design temperature.

Cooling (one zone or room)
sq ft

Defaults to your floor area, treating the home as one open zone. For separate rooms or mini-split heads, size each area on its own. Chart covers 100 to 2,499 sq ft with 8-ft ceilings.

Heating load at 5 °F
22,829 Btu/h1.9 tons
Cooling capacity (one zone)
30,000 Btu/h2.5 tons
Heat loss rate
380 Btu/h per °F

Choose a heat pump that delivers the heating load at your design temperature (check the manufacturer’s capacity at that temperature, not the nominal rating). This is a screening estimate, not an ACCA Manual J calculation.

Formula: heat loss rate = annual heat ÷ (degree days × 24); heating load = heat loss rate × (65 °F − design temperature). Cooling: ENERGY STAR room sizing chart, ±10% for shade or sun, +600 Btu/h per person above two, +4,000 Btu/h for a kitchen, rounded down to the nearest 1,000.

Inputs used: heat: 36.6 million Btu/yr; degree days: 4,008; design temperature: 5 °F; zone: 1,614 sq ft.

These are estimates, not financial advice.

Heating use: U.S. Energy Information Administration, Residential Energy Consumption Survey (RECS) 2020. Degree days: NOAA National Centers for Environmental Information, Climate at a Glance, 2016–2025 average (DC uses Maryland; no statewide series for Alaska and Hawaii). Cooling: ENERGY STAR room air conditioner sizing chart.

Worked examples in three states

Average-size gas-heated home in each state, example design temperature 5 °F (use your local value).

StateDegree daysHeat/yrHeating loadTons
North Dakota8,97555.8 MMBtu15,543 Btu/h1.3
Oregon5,12235.3 MMBtu17,230 Btu/h1.4
Florida5227.2 MMBtu34,483 Btu/h2.9

ENERGY STAR cooling capacity chart (one room or zone)

Area to coolCapacity
100 up to 150 sq ft5,000 Btu/h
150 up to 250 sq ft6,000 Btu/h
250 up to 300 sq ft7,000 Btu/h
300 up to 350 sq ft8,000 Btu/h
350 up to 400 sq ft9,000 Btu/h
400 up to 450 sq ft10,000 Btu/h
450 up to 550 sq ft12,000 Btu/h
550 up to 700 sq ft14,000 Btu/h
700 up to 1,000 sq ft18,000 Btu/h
1,000 up to 1,200 sq ft21,000 Btu/h
1,200 up to 1,400 sq ft23,000 Btu/h
1,400 up to 1,500 sq ft24,000 Btu/h
1,500 up to 2,000 sq ft30,000 Btu/h
2,000 up to 2,500 sq ft34,000 Btu/h

Source: ENERGY STAR (8-ft ceilings). Adjust −10% for heavy shade, +10% for very sunny rooms, +600 Btu/h per person above two, +4,000 Btu/h for kitchens; round down to the nearest 1,000. Example: 1,614 sq ft → 30,000 Btu/h.

How we calculate

heat loss rate (Btu/h·°F) = annual heat delivered ÷ (heating degree days × 24); heating load = heat loss rate × (65 °F − design temperature). Annual heat: EIA RECS 2020 average gas heating use for the state × 80% furnace efficiency, scaled by floor area and by NOAA degree days (typical ÷ 2020). This is a screening estimate, not a Manual J calculation.

Frequently asked questions

What size heat pump do I need?

One that can deliver your home’s heating load at your local design temperature, and enough cooling for the space. The best inputs are your own heating bills; a contractor should confirm with an ACCA Manual J load calculation before you buy.

Why not just use square feet?

Two homes of the same size can need very different heat because of insulation, air leakage, windows and climate. Annual heating use already reflects those differences, which is why this calculator starts from heat use and degree days.

What is a design temperature?

A cold outdoor temperature that is only rarely reached at your location, used to size heating equipment. Your HVAC contractor or local building department can tell you the value for your area.

Is the cooling estimate for the whole house?

The ENERGY STAR chart is for sizing a unit for one room or zone, with 8-foot ceilings, from 100 to 2,499 sq ft. For multi-zone ductless systems, size each zone separately.

Data last updated: