Heat Pump Breaker & Wire Size Calculator
Find the breaker amperage and copper wire gauge from your heat pump nameplate (MCA & MOCP).
Size from the nameplate, not the tonnage
The correct breaker and wire size come from two numbers on the heat pump's rating plate (nameplate), not from its tonnage: MCA (Minimum Circuit Ampacity) sizes the wire, and MOCP (Maximum Overcurrent Protection) sets the largest allowable breaker. Enter those above for the answer.
Copper wire size by MCA (75°C)
| MCA | Copper wire | Typical breaker (MOCP) |
|---|---|---|
| ≤ 20 A | #12 AWG | 20 A max |
| ≤ 30 A | #10 AWG | 30 A max |
| ≤ 40 A | #8 AWG | 40–45 A |
| ≤ 55 A | #6 AWG | 50–60 A |
Rough guide by size (estimate only)
If you do not have the nameplate, residential heat pumps commonly land around: 1.5–2 tons → 20–30 A breaker / #10 wire; 2.5–3 tons → 30–40 A / #10–#8; 3.5–5 tons → 40–60 A / #8–#6. These are estimates only — the nameplate MCA/MOCP and a licensed electrician are the authority, and all work must meet the NEC and local code.
Frequently asked questions
What size breaker for a heat pump?
Use a breaker no larger than the nameplate MOCP (Max Overcurrent Protection) — commonly 30–50 A for residential heat pumps. Never exceed the MOCP.
What size wire for a heat pump?
Size the copper wire to the nameplate MCA (Minimum Circuit Ampacity) using the NEC 75°C column — e.g. 25 A MCA → #10 AWG, 40 A → #8. Always verify with the nameplate.
Where do I find MCA and MOCP?
On the heat pump rating plate (nameplate) on the outdoor unit. These two numbers, not the tonnage, determine the breaker and wire.
Can I use a 30-amp breaker for a heat pump?
Only if the nameplate MOCP is 30 A or higher and the MCA fits #10 wire. Never exceed the MOCP printed on the unit.
Does a heat pump need a dedicated circuit?
Yes — the outdoor unit needs its own dedicated 240-volt circuit sized to its nameplate; the indoor air handler usually has a separate circuit.
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⚠️ Rule-of-thumb estimate, not a substitute for a professional Manual J load calculation. Based on US DOE / ENERGY STAR guidance.