Heat Pump Sizing Calculator — Free Online Calculator
A heat pump must handle both the summer cooling load and the winter heating load, and in most US homes those two numbers are different. This tool estimates each from your home size, climate zone, insulation, and ceiling height, recommends a tonnage, and flags when the heating load outruns cooling so you know whether you need a cold-climate unit or backup heat.
Need just cooling or heating load separately? Start with the BTU Calculator (cooling) or the Furnace BTU Calculator — then return here to size the heat pump.
Size your heat pump
Recommended heat pump size
Cooling load
36,000 BTU
Heating load
54,000 BTU
Sizing guidance
Heating load is moderately higher than cooling (typical in mixed climates) — size to the cooling load shown and cover the heating shortfall with a variable-speed/cold-climate unit or modest backup heat.
See the breakdown
This is a planning estimate. For permits, equipment warranties, and final installation, confirm with a full ACCA Manual J load calculation.
Heat pump load by climate zone
1,800 sq ft · 8 ft ceilings · average insulation. Your numbers scale with size, insulation, and ceiling height.
| Climate (IECC zone) | Heating BTU/sq ft | Cooling factor | Cooling load (tons) | Heating load |
|---|---|---|---|---|
| Hot (1–2) | 20 | ×1.2 | 43,200 BTU (3.5 tons) | 36,000 BTU |
| Warm (3) | 25 | ×1.1 | 39,600 BTU (3.5 tons) | 45,000 BTU |
| Mixed (4) | 30 | ×1.0 | 36,000 BTU (3 tons) | 54,000 BTU |
| Cold (5) | 35 | ×0.95 | 34,200 BTU (3 tons) | 63,000 BTU |
| Very cold (6–7) | 40 | ×0.9 | 32,400 BTU (3 tons) | 72,000 BTU |
Planning estimate for comparison only. Confirm final sizing with a full ACCA Manual J load calculation.
Sources & standards: U.S. DOE Energy Saver — Air-Source Heat Pump Systems · ENERGY STAR Cold Climate Heat Pump specification (capacity at 5°F, HSPF2 ≥ 8.5) · PNNL Building America — Cold-Climate Heat Pump Sizing & Selection · ACCA Manual J (load calculation standard) .
The formula, explained in plain English
A heat pump is sized in two passes — once for cooling, once for heating — and then you check whether the two agree. Here is exactly what this calculator does.
Why size to cooling?
An oversized AC short-cycles and won't dehumidify, so the cooling load sets the compressor size for most of the country.
Where heating wins
In cold zones the heating load is far larger — that's the balance-point gap, covered by aux heat or a cold-climate inverter unit.
Heating BTU per sq ft by zone
Roughly 20 BTU/sq ft in hot climates rising to about 40 BTU/sq ft in very cold zones — the single biggest driver of the heating number.
Cold-climate heat pumps
ENERGY STAR cold-climate models hold at least 70% of rated capacity at 5°F and carry an HSPF2 of 8.5 or higher, so they heat efficiently in winter.
Worked examples
Three scenarios showing how the cooling and heating loads diverge across climates — and what that means for the equipment you choose.
Hot climate, cooling-led — 1,500 sq ft, Gulf Coast
8 ft ceilings · hot zone (heating 20 BTU/sq ft, cooling ×1.2) · average insulation.
heating = 1,500 × 20 = 30,000 BTU
Result: cooling leads; a single 3-ton heat pump covers both with margin.
Cold climate, heating-led — 2,000 sq ft, Zone 5
8 ft ceilings · cold zone (heating 35 BTU/sq ft, cooling ×0.95) · average insulation.
heating = 2,000 × 35 = 70,000 BTU
Result: heating nearly doubles cooling — choose a cold-climate heat pump sized toward heating, or add backup heat below the balance point.
Well-insulated mixed home — 1,800 sq ft, excellent insulation (×0.9)
8 ft ceilings · mixed zone (heating 30 BTU/sq ft, cooling ×1.0) · excellent insulation (×0.9).
heating = 1,800 × 30 × 0.9 = 48,600 BTU
Result: a tighter envelope trims both loads; size to ~3 tons cooling and plan a modest heating supplement.
Frequently asked questions
Common questions about heat pump sizing, heating vs. cooling loads, and cold-climate units.
What size heat pump do I need?
Size to the larger of your heating and cooling loads, but in practice most US homes size the heat pump to the cooling load (≈20 BTU/sq ft adjusted for climate, sun, insulation) so it dehumidifies properly, then cover any winter shortfall with backup heat or a cold-climate model. A 1,800 sq ft mixed-climate home is typically 3 tons.
Are heat pumps sized differently from air conditioners?
The cooling side is sized just like an AC. The difference is you must also check the heating load, which in cold climates is much larger — that's why heat pump sizing adds a balance-point check.
What is a heat pump's balance point?
The outdoor temperature where the heat pump's output exactly equals the home's heat loss. Above it the heat pump handles everything; below it you need supplemental/backup heat. Cold-climate (inverter) heat pumps push the balance point much lower.
Do I need a cold-climate heat pump?
If your heating load is far above your cooling load (Zone 5+), yes — ENERGY STAR cold-climate models keep ≥70% of rated capacity at 5°F and have HSPF2 ≥ 8.5, so they heat efficiently without leaning on resistance backup.
Should I oversize a heat pump for cold winters?
Not by oversizing the cooling capacity — that causes short-cycling and poor summer humidity control. Instead pick a cold-climate unit or add staged backup heat. Right-size to cooling, solve heating separately.
How accurate is this vs. a Manual J?
It's a solid planning estimate using climate-zone BTU-per-sq-ft rules. A full ACCA Manual J accounts for windows, orientation, infiltration, and duct losses and is required for permits and warranties. Use this to plan, a Manual J to install.
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Trusted Heat Pump Sizing Standards
The BTU-per-sq-ft targets, balance-point checks, and cold-climate criteria on this page trace back to load-calculation and equipment-selection standards. These organisations publish the specifications contractors rely on for permit-grade heat pump sizing.
Residential load-calculation standard — the BTU-per-sq-ft and climate-zone method contractors use for permit-grade heating and cooling sizing.
Equipment-selection protocol — matches Manual J loads to a heat pump model that delivers the right capacity at design conditions.
Energy Saver guide to air-source heat pump sizing, efficiency, supplemental heat, and the airflow each ton of capacity needs.
Cold-climate heat pump criteria: HSPF2 ≥ 8.5, ≥70% heating capacity at 5°F, and COP ≥ 1.75 — the spec this calculator flags in northern zones.
Cold-climate heat pump sizing and selection guide — balance-point analysis, backup-heat strategies, and climate-zone equipment choices.
Directory of certified heat pump ratings — heating and cooling capacity, HSPF2/SEER2, and low-ambient performance at standard test points.