Heat Pump System GuideThe electrical work behind a heat pump is often the part a homeowner discovers late, sometimes after the equipment is already chosen. This guide lays out the wiring, breaker, and panel questions using nameplate rules and NEC references, so you can tell in advance whether your existing panel can carry the load.
Voltage Depends on the System, Not Just the Size
Mini-split heat pumps split roughly into low-voltage and line-voltage groups. Smaller units in the 9,000 to 12,000 BTU range often run on 115V with a single-pole breaker, while units at 18,000 BTU and larger usually need 208 to 230V with a double-pole breaker, and nearly all multi-zone systems run at the higher voltage.
Size is a guide, not a guarantee. Some small units still require 230V, so the nameplate is the only reliable source for the voltage a given model needs.
Before assuming a project only needs a standard outlet circuit, confirm the voltage on the specific unit. A 240V requirement changes the breaker, the wire, and sometimes whether the panel has room.
Read MCA and MOP Before Picking a Breaker
Two nameplate values control the circuit. The Minimum Circuit Ampacity (MCA) determines the smallest wire gauge and circuit size you can use, and the Maximum Overcurrent Protection (MOP, sometimes labeled MOCP) sets the largest breaker size allowed. The breaker must be equal to or less than the MOP, and the circuit must be sized for at least the MCA.
The key discipline is that neither number should be guessed from the BTU rating. A general rule of thumb is a starting point for planning, but the nameplate MCA and MOP are what the installation must actually follow.
As a rough planning reference, small 9,000 to 12,000 BTU units commonly land around 15 to 20 amps, medium 15,000 to 18,000 BTU units around 20 to 25 amps, and large 24,000 BTU and up units around 30 to 40 amps. Confirm against the specific unit.
Dedicated Circuits and the Outdoor Disconnect
Heat pump equipment is not meant to share a circuit. NEC Article 440 requires a dedicated circuit for the HVAC branch circuit so that other appliances cannot cause voltage drops or nuisance trips, and each unit runs on its own circuit from the panel.
The code also requires a service disconnect. NEC 440.14 mandates a disconnect within sight of the outdoor unit so the equipment can be safely de-energized for service. A separate source confirms that a disconnect at the outdoor unit is required by code in most places for mini-split installations.
These are not optional extras. Budget for a dedicated circuit and an outdoor disconnect on any heat pump install, and treat their absence in a quote as a question to raise.
When the Panel Itself Needs an Upgrade
The panel is the real constraint for many older homes. A 100-amp panel, common in pre-1980 homes, is often at or near capacity with no room for additional breakers, and adding a 20 to 30 amp mini-split circuit can push it beyond safe capacity. A 200-amp panel, common in newer homes, generally has adequate capacity and usually has open breaker spaces.
Two different problems can force electrical work. A 200-amp panel may have capacity but every breaker space occupied, which points to adding a subpanel or replacing the panel. A 100-amp panel that is already at or near capacity may need an upgrade to 150 to 200 amps to safely carry the new load.
The load side matters too. The NEC allows panels to be loaded to 80 percent of the main breaker capacity for continuous loads, so a 100-amp panel safely supports about 80 amps of continuous load. That headroom, not just the label on the panel, decides whether a new circuit fits.
Wire Sizing Follows the Circuit
Wire gauge is set by the circuit ampacity, not chosen freely. As an example, systems with 30-amp circuits, such as some 36,000 BTU units, call for 10-gauge wire, while the run from the breaker to the disconnect box commonly uses 12/3 or 12/2, with the exact choice depending on power draw, distance, and local code.
Between the outdoor and indoor units, a 14/4 stranded cable is a common choice, providing two 14-gauge power conductors, one communication wire, and a ground.
These are examples tied to specific amperages, not a universal wire size. The MCA on the nameplate and the run length are what actually determine the correct gauge for a given install.
Frequently asked questions
Do all heat pumps need a 240V circuit?
No. Smaller mini-splits in the 9,000 to 12,000 BTU range often run on 115V, while 18,000 BTU and larger units and nearly all multi-zone systems typically need 208 to 230V. The nameplate is the only reliable source for a given model.
How do I pick the right breaker size?
Use the nameplate values, not the BTU rating. MCA sets the minimum wire and circuit size, and MOP or MOCP sets the maximum breaker size. The breaker must be equal to or less than the MOP.
Is a dedicated circuit really required?
Yes. NEC Article 440 requires a dedicated circuit for the HVAC branch circuit, and NEC 440.14 requires a disconnect within sight of the outdoor unit.
When does a heat pump need a panel upgrade?
When there is no safe capacity or no open breaker space. A 100-amp panel at or near capacity may need an upgrade to 150 to 200 amps, while a full 200-amp panel may need a subpanel or replacement. The NEC 80 percent continuous-load limit determines the usable headroom.