How to Wire a 240V Garage Heater? | NEC Compliant Setup

Wiring a 240V garage heater requires a dual-pole breaker, 10 or 8-gauge copper wire through conduit, and connecting the two hot legs directly to the heater terminals without a neutral wire.

A 240V garage heater delivers serious heat, but the wiring must follow code. The job takes a correctly sized dual-pole breaker, copper wire in the right gauge, conduit protection from panel to heater, and a hard-wired connection at the unit. This guide covers the materials you need, the step-by-step procedure, and the mistakes that trip up DIY installs.

What Do You Need to Wire a 240V Garage Heater?

The breaker and wire size depend on the heater’s wattage. A 5,000–7,500W unit needs a 30A dual-pole breaker with #10 AWG copper wire. An 8,500–10,000W unit needs a 40A breaker with #8 AWG copper wire. Aluminum wire is not permitted for this application — copper only.

You also need rigid metal conduit or EMT from the panel to the heater, plus flexible appliance whip near the heater entry. No neutral wire is required: 240V heaters use two hot legs (Red and Black) plus a ground (Green or bare copper). If your thermostat is line-voltage, it must be rated for 240V and use cable rated for 300V. Readers shopping for a unit can check our tested roundup of the best 240V electric garage heaters for current model recommendations.

Step-by-Step Wiring Procedure

1. Turn off power. Shut off the main breaker or the specific garage circuit before opening the panel.

2. Verify panel space. Confirm you have open slots for a new dual-pole breaker.

3. Install the breaker. Mount a 30A or 40A dual-pole breaker. Connect Red and Black to the breaker terminals and the ground wire to the ground bar.

4. Run conduit. Install conduit from the panel to the heater location. Use flexible appliance whip near the heater for easier connections.

5. Pull wire. Feed #10 or #8 AWG copper wire through the conduit. If using a thermostat, verify the wire is rated for 300V.

6. Connect at the heater. Attach Red to the L1 terminal and Black to the L2 terminal. Connect Green or bare copper to the ground terminal. Cap any white neutral wire — do not connect it.

7. Install thermostat or contactor. Wire a 240V line-voltage thermostat in series with one hot leg. If your heater includes a contactor, wire its coil to match the switch voltage.

8. Secure and test. Mount the heater at least 8 feet above the floor and 8 inches from vertical surfaces. Restore power and verify operation.

Common Wiring Mistakes to Avoid

Using aluminum wire instead of copper, installing a neutral where none is needed, and undersizing the breaker or wire for the heater’s wattage are the three most frequent errors. Each creates a safety hazard or code violation. Skipping conduit is another common mistake — flexible wire without conduit protection fails inspection. Most 240V heaters must be hard-wired, not plugged into a standard receptacle, unless a dedicated 240V outlet and matching plug are installed per code.

Here is how common heater models map to their circuit requirements:

Always confirm the manufacturer manual for your specific unit before purchasing materials. Your garage should have at least 50A service capacity to support a 10,000W heater.

Matching the right wire gauge, breaker size, and connections to your heater is the entire difference between a safe install and a hazardous one. Follow the procedure above, use copper wire only, and have a certified electrician handle the panel work.