What Size Wire for a Garage Heater?
Wire and breaker sizing for a Garage Heater — 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.
Copper
10 AWG
On a 30A 240V circuit at 75°C terminations.
Aluminum
8
Protected by a 30A breaker (NEC 240.6).
Voltage
240V
Breaker
30A
Connection
Hardwired
GFCI
Not required
Garage Heater Circuit Details
- Electric garage/shop heaters are continuous loads — size at 125%. A 5,000W 240V heater draws ~21A and needs a 30A circuit (10 AWG).
- A 7,500W heater needs a 40A circuit (8 AWG).
- Confirm the wattage and that the circuit is dedicated.
Long run to your garage heater?
Over distance, voltage drop can require a larger wire than the table above. See the 30A wire size by distance:
Size it for your exact install
Open the calculator pre-filled with 30A at 240V to add distance, material and temperature.