What Size Wire for an Electric Furnace?
Wire and breaker sizing for an Electric Furnace — the typical 240V circuit, plus the code details (NEC 310.16) that change the answer.
Calculations are built on the 2023 National Electrical Code (NEC) and cross-checked against the published code tables. How we verify. Last reviewed June 2026.
On a 60A 240V circuit at 75°C terminations. 60°C terminations: 4.
Protected by a 60A breaker (NEC 240.6).
Electric Furnace current varies by model. The size above is the common case — always size the conductor to the unit’s nameplate rating and protect it at the labeled maximum breaker/fuse.
Electric Furnace Circuit Details
- Electric furnaces / air handlers with heat strips are large continuous loads — size to the nameplate, often 60A (6 AWG copper) and up.
- Big units split the heat strips across two or more circuits.
- Electric heat is continuous, so conductors are sized at 125% of the heater load.
Long run to your electric furnace?
Over distance, voltage drop can require a larger wire than the table above. See the 60A wire size by distance:
Size it for your exact install
Open the calculator pre-filled with 60A at 240V to add distance, material and temperature.