What Size Heat Pump Do You Need? Free Sizing Estimator

About 20 Btu per square foot (Efficiency Maine’s published method): 2,000 sq ft brackets to 32,000–40,000 Btu/h — enter your size and climate zone.

A bracketed capacity range, not a specWhat this tool outputs

Square footage + DOE/IECC climate zoneInputs used

Efficiency Maine worksheet + NEEP medians (cited)Range source

Updated September 2026 · Source: EIA Electric Power Monthly Table 5.6.A (July 2026 data) · next EIA update ~Oct 23

By SolarCostData Data Desk · Reviewed September 2026 · Corrections log

On this page: Calculator Table How we calculated Sources

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Conditioned floor area (sq ft) State — sets your predominant DOE/IECC climate zone

What changes if… Floor area

Secondary control over the same field; the numeric input stays the precise way in. The URL keeps your scenario.

Your climate zone: —

Screening heat load: —

Program sizing band (80–100%): —

Screening rule: "Square footage method: >/=20 Btu/hour/square foot of any area that: is currently served by any heating system (existing homes), OR will be heated (new construction)" — Efficiency Maine — Residential Heat Pump Rebate Claim Form (Sizing Worksheet), document dated 2026-08-28. The form scopes it as “suitable for homes with typical insulation and air sealing.” Climate zone: predominant IECC zone per state, tallied from the DOE/PNNL county table (a state can span zones — your county decides). Capacity classes below: NEEP cold-climate database medians.

What this tool outputs: A bracketed capacity range, not a spec
Inputs used: Square footage + DOE/IECC climate zone
Range source: Efficiency Maine worksheet + NEEP medians (cited)
What it can't see: Insulation, windows, air sealing, ceiling height
The real answer: A contractor's Manual J load calculation
Oversizing risk: Short cycling and weaker dehumidification — not just cost

Why this number

Heat pump sizing rules-of-thumb combine your home’s square footage with its DOE/IECC climate zone to produce a rough capacity range, drawn from published program guidance — Efficiency Maine’s sizing worksheet rule and NEEP cold-climate database medians, each cited next to your result. A range exists because square footage alone hides everything that actually drives heat loss: insulation levels, window area and glazing, air sealing, ceiling height, and how many walls face outside. Climate zone narrows the range by reflecting how cold your region’s design temperature runs, but it still describes a typical house in that zone, not yours specifically. This tool brackets a plausible capacity — it never specifies one, because specifying one is a load calculation, not a lookup. The only way to size a heat pump for your actual home is a Manual J load calculation performed by a contractor who accounts for its real construction.

Square footage and climate zone are the two numbers everyone already has — this tool turns them into a published, cited bracket and nothing more.

NEEP cold-climate medians: what each size class delivers

Median heating capacity and COP of NEEP-listed cold-climate heat pumps by size class, at 47, 17 and 5 degrees Fahrenheit
Class	47°F BTU/hr	47°F COP	17°F BTU/hr	17°F COP	5°F BTU/hr	5°F COP
1.5-ton ducted	22000	3.3	18520	2.3	16900	2
2.5-ton ducted	35000	3.24	31200	2.27	27000	1.96
2-ton ducted	29000	3.27	22203	2.34	20900	1.97
3.5-ton ducted	47000	3.24	39500	2.21	34000	2
3-ton ducted	42000	3.2	36000	2.17	33000	1.9
4-ton ducted	50000	3.19	41500	2.29	40000	1.9
5-ton ducted	64500	3.1	50400	2.3	48500	1.91
1.5-ton ductless	22000	3.22	18500	2.24	16950	1.98
2.5-ton ductless	34050	3.32	27400	2.35	24500	2
2-ton ductless	29200	3.06	23600	2.2	20000	2
3.5-ton ductless	48000	3.27	34600	2.25	34000	2
3-ton ductless	43200	3.1	35200	2.23	32700	1.98
4-ton ductless	55000	3.09	44550	2.26	39500	2

Medians of the NEEP cold-climate ASHP database (ENERGY STAR cold-climate subset), deduplicated by outdoor unit; per-class sample sizes shown. Source: ashp.neep.org. Capacity falls with temperature — the 5°F column is the honest one for a cold-zone design conversation.

Square footage and climate zone are the two numbers everyone already has, which is exactly why sizing rules-of-thumb are built on them. This tool takes both and returns a bracketed capacity range pulled from published efficiency-program guidance — Efficiency Maine’s sizing worksheet and NEEP cold-climate medians, cited next to your result — not a number fitted or invented for your specific house.

What a rule-of-thumb can tell you — and what it can’t

Climate zone captures how demanding your region’s design temperature is: a Zone 2 home in Houston and a Zone 6 home in Minneapolis need different capacity even at identical square footage, because the outdoor design temperature each system has to handle is different. Combining zone with floor area gives a plausible range for a “typical” home of that size in that zone — a reasonable first gut-check, or a sanity check on a quote you already have.

What it can’t do is see your actual house. Square footage says nothing about insulation R-values, window area and glazing type, air sealing, ceiling height, or how many walls and how much roof face the outdoors — and two homes of identical size in the same zone can have meaningfully different heat loss from those factors alone. A rule-of-thumb range can’t narrow past what square footage and climate zone actually encode. Only a Manual J load calculation — a contractor measuring your home’s real construction, room by room — produces an actual number, and oversizing that number has real costs of its own: short cycling, weaker dehumidification, added wear. The goal is the contractor’s figure, not the top of this bracket.

Next steps

With a range in hand, price what a heat pump actually costs to run against a furnace using the heat pump vs furnace cost calculator , see how your climate’s degree-days shape a typical season on the winter heating page, and if you’re weighing whether to keep gas as backup rather than size around the coldest day alone, the dual-fuel switchover calculator handles that question directly.

Frequently asked questions

Why can't this replace a Manual J load calculation?

A square-footage-and-climate-zone rule of thumb averages over every home of that size in that zone. Manual J instead calculates room-by-room heat loss and heat gain from your home’s actual measurements — insulation R-values, window U-factors and orientation, air leakage, duct location. Two homes of identical size in the same zone can have genuinely different loads for reasons a bracket can’t see, which is exactly what a full ACCA Manual J calculation is built to capture and a rule-of-thumb is not.

Does oversizing a heat pump actually matter?

Yes, and it’s not only a cost question. An oversized unit satisfies the thermostat faster, which means it cycles on and off more often — that short-cycling reduces dehumidification in cooling mode, adds mechanical wear, and can undercut the steady, efficient operation a heat pump is bought for. Undersizing carries its own risk: leaning on backup heat more often at the coldest hours. Right-sizing is a genuine engineering trade-off that only a load calculation resolves.

What climate zone am I in?

The Department of Energy assigns every U.S. county to one of eight IECC climate zones based on long-term temperature data, and that assignment is what building codes and efficiency programs use for equipment guidance. This page links a zone locator so you can look up your own county directly rather than guess from a map.

Should I size by square feet or actual heat loss?

Square footage is a proxy; actual heat loss — the BTU/hr your house loses at your region’s design temperature — is the real quantity equipment capacity has to match. Two homes of identical square footage can have very different heat loss depending on their envelope. Square feet gives a cheap, fast first estimate; actual heat loss only comes from a room-by-room calculation, which is what Manual J performs.

How we calculated this

Range = square feet × 20 Btu/sqft (the published Efficiency Maine square-footage method) × 0.8–1.0. The climate-zone row shows the NEEP median 5°F capacity of the unit class nearest that load. No load calculation is performed; only a Manual J can specify the real number.

Sources: U.S. Energy Information Administration (EIA) electricity rates · DSIRE incentive records · public IRS/OBBBA guidance. Figures are modeled estimates, not quotes or tax advice. See our methodology.

Where to go next

Cost to heat a home, state by state — Once sized, what the running cost looks like per MMBtu in 20 cold states — gas, propane, oil, heat pump, resistance.
Heat pump vs furnace cost calculator — Once you have a size range, price what running each option actually costs at your rates.
Winter heating costs — See how your climate’s degree-days translate into a typical winter bill, fuel by fuel.
Dual-fuel switchover calculator — Deciding whether to keep a furnace as backup rather than size the heat pump for the coldest day alone.