Heat pump electrical requirements

Every heat pump outdoor unit has a nameplate that lists two numbers the electrician sizes the circuit from: MCA (minimum circuit ampacity) and MOCP (maximum overcurrent protection, sometimes printed as maximum fuse or breaker size). The wire must be rated for at least the MCA, and the breaker or fuse must not exceed the MOCP. These come from the specific unit, so two heat pumps of the same tonnage can need different circuits. See MCA and MOCP.

Where the numbers come from

The National Electrical Code, Article 440, covers air conditioning and refrigeration equipment, including heat pumps. As summarized by EC&M:^{[Source 1]}

• NEC 440.4(B) requires the nameplate to show "minimum conductor ampacity" and "the maximum rating of the branch-circuit short-circuit and ground-fault protective device."
• Conductors are sized at 125% of the compressor's rated-load current (440.32 and 440.33). The MCA on the nameplate already includes this.
• The short-circuit protection for a single compressor is generally limited to 175% of compressor current, or up to 225% if the unit will not start at the lower size (440.22). The MOCP on the nameplate reflects this.

In practice, the electrician reads MCA and MOCP off the nameplate or the installation manual rather than recalculating them. Some examples from manufacturer documents:

Unit	MCA	Max fuse / breaker
Mitsubishi MUZ-FS06/09/12 (ductless, single zone)	10 A	15 A[Source 3]
Mitsubishi MXZ-C multi-zone (range across the models in one manual)	28.9 to 31.9 A	40 A[Source 4]

Disconnect

A disconnect switch is required near the outdoor unit. The DOE and New Buildings Institute inspection checklist states: "A disconnecting means... is installed within sight from the ASHP and is readily accessible. (NEC 440.11, NEC 440.14)."^{[Source 2]} Daikin's manual adds: "Local codes often require a disconnect switch located near the unit; do not install the switch on the unit."^{[Source 5]}

Backup heat circuits

If the system includes electric resistance backup heat in an indoor air handler, the air handler carries its own nameplate electrical ratings, and its circuit is sized from those, not from the outdoor unit's. See Aux heat (auxiliary heat).

Does the panel have room?

Panel size (for example 100 or 200 amps) is not the answer by itself. The question is whether the calculated load, including the new heat pump, fits within the service. The DOE/NBI checklist requires that panel capacity cover the service load calculated under NEC Article 220.^{[Source 2]}

For existing homes, the NEC gives two common methods. As described by Lawrence Berkeley National Laboratory (LBNL):^{[Source 6]}

• NEC 220.83, inventory of loads. Count the nameplate loads in the house. With new heating or cooling, the calculation counts all of the first 8,000 watts, plus 40% of the remaining loads, plus the larger of the heating or cooling load.
• NEC 220.87, measured demand. Use utility metering data for the home's actual peak demand, add 25%, then add new loads at their full nameplate rating. LBNL's example: a 100-amp service is 24 kW; a measured 4 kW peak times 1.25 is 5 kW, leaving 19 kW for new nameplate load.

Measured demand can be well below the nameplate total. An LBNL presentation cites a Vermont heat pump program in which 10,000 heat pumps "on average added only ~200 W," against a 3,600-watt nameplate.^{[Source 7]}

The 2026 NEC changed this

In the 2026 edition of the NEC, the existing-dwelling calculation moved to section 120.83, and LBNL reports that new heat pumps count at 50% of nameplate in that method, down from the full nameplate rating before.^{[Source 7]} Which edition applies depends on what your state or city has adopted, so the same house can pass in one jurisdiction and need a service upgrade in another. Ask the electrician which NEC edition the local inspector uses.

How often panels need replacing

LBNL summarizes field data: in California's TECH Clean California program, 6% of 21,146 heat pump projects replaced the panel, and a cold-climate study by Cadmus found 8% needed a service panel replacement.^{[Source 7]} Those shares reflect those programs and housing stocks; your home's result depends on its existing loads and service size.

Ask for the load calculation in writing before agreeing to a panel or service upgrade. Permits for the electrical work are covered in Permits and inspections for heat pumps.