How Many Amps Does a Heat Pump Use?
Updated · By Dariusz
A heat pump's current depends on its size, whether it's variable-speed, and — most of all — whether the indoor unit has electric backup heat. The outdoor unit of a typical residential heat pump runs on a 240 V circuit; backup heat strips can add more load than the outdoor unit itself. The nameplate tells you exactly what to plan for.
Read the nameplate, not the tonnage
Every outdoor unit has a label with two numbers that matter:1
| Label | Meaning | Use it for |
|---|---|---|
| MCA | Minimum circuit ampacity | Planning load; multiply by 240 for VA |
| MOCP | Maximum overcurrent protection | The largest breaker allowed |
Tonnage alone won't tell you the current. Two 3-ton units from different makers can have quite different MCA ratings, and variable-speed models often draw less at part load.
Don't forget backup heat
Many air handlers include electric resistance strips for very cold days or defrost. They're rated in kilowatts on the air handler's label — and under NEC® 220.83(B) they count at 100% as new heating.2 Ask your installer whether your system needs them and at what size; that single choice can decide whether your panel has room.
What it means for your panel
When you add a heat pump, the load calculation counts the heating and cooling at 100% and discounts most other loads. In many smaller homes with gas cooking and drying, a heat pump fits on 100 A service with room to spare — the worked example below shows one. Electric ranges, dryers and an EV charger change that quickly.
Check your own numbers with the free check, and use the load calculation guide to follow each step.
Technical notes
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These numbers come from NEC® Article 440 (air-conditioning and refrigeration equipment). MCA is roughly 125% of the largest compressor's rated-load current plus the other motors (440.33). The breaker may be up to 175% of the compressor current, or 225% if needed for starting (440.22(A)) — which is why MOCP is larger than MCA. Always use the values printed on your unit. Source: NFPA 70 (NEC®), free access. ↩
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When heating and cooling can't run at the same time, 220.60 lets the calculation count only the larger of the two. With backup strips, heating is usually the larger load. Our quick check counts both a new heat pump and existing resistance heat, which errs on the safe side. The U.S. Department of Energy notes that because resistance elements are inefficient, their use should be kept to a minimum. Sources: DOE FEMP, air-source heat pumps; NFPA 70 (NEC®), free access. ↩
Worked example · NEC® 2023 220.83(B)
A 1,500 ft² home on 100 A service with gas cooking and drying, adding a 3-ton heat pump
| General lighting and receptacles: 1,500 ft² × 3 VA | 4,500 VA |
| Kitchen small-appliance circuits: 2 × 1,500 VA | 3,000 VA |
| Laundry circuits: 1 × 1,500 VA | 1,500 VA |
| dishwasher | 1,200 VA |
| microwave | 1,500 VA |
| heatPump (heating/cooling) | 7,200 VA |
| First 8,000 VA at 100% | 8,000 VA |
| Remainder 3,700 VA at 40% | 1,480 VA |
| Heating and cooling at 100% | 7,200 VA |
| Demand ÷ 240 V | 69.5 A of 100 A |
Green — fits with room to spare · 31 A free
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Questions
What do MCA and MOCP mean on a heat pump?
MCA (minimum circuit ampacity) sizes the wire. MOCP (maximum overcurrent protection) is the largest breaker allowed. Neither is the running current, but MCA is a good number for planning.
Do I need to count the backup heat strips?
Yes, if your air handler has electric resistance backup. Heat strips often draw more than the outdoor unit and count at 100% as new heating.
Does replacing a gas furnace with a heat pump add load?
Yes. The gas furnace used little electricity; the heat pump and any backup strips are new electric heating, so the calculation counts them in full.