Garage Heater Electrical Requirements

Why this is the first spec to check, not the last

Most people shop garage heaters on BTU or wattage, pick the one sized for their garage, and discover the electrical requirement after it arrives. That is the wrong order, because the circuit is frequently the binding constraint — a 7,500W heater is useless in a garage whose panel has no room for a 40A double-pole breaker.

Check the panel first. It narrows the choice to one of three groups immediately, and it is the difference between a $60 install and a $900 one.

The 120V group: 1,500W and nothing more

Every plug-in 120V heater, of every type, tops out at about 1,500W, because that is 12.5 amps and a 15A circuit will not carry more continuously. There is no 120V heater that breaks this rule, and a listing implying otherwise is describing something other than sustained output.

What 1,500W buys: the Dura Heat EUH1500 publishes 5,120 BTU and up to 250 square feet of coverage with a built-in thermostat, which is a one-car bay at best and only if it is insulated. That is the honest limit of the group.

• Do give it a dedicated 15A or 20A circuit if you can. Sharing with a compressor or a table saw will trip the breaker when the motor starts.
• Do not run it on an extension cord. A 12.5 amp continuous load on a thin cord is the classic garage fire. If it must be plugged in away from the outlet, the cord has to be rated for the full load and as short as possible.
• Do check the plug type. Some 120V heaters at the top of the range use a 20A plug with a sideways blade, which will not fit a standard 15A receptacle.

The full picture at this wattage, including what it will and will not heat, is in the best 120V garage heaters.

The 240V group: 5,000W and 7,500W

This is where garage heating actually starts, and where an electrician enters the picture. Both wattages need a dedicated 240V circuit; the difference between them is how likely your existing panel is to accommodate it.

5,000W draws roughly 21 amps and typically wants a 30A circuit. The Comfort Zone CZ220 is the example here: 5,000W, 240V, fan-forced, ceiling mount, heavy-gauge steel, with a dual-knob thermostat. Crude controls, but it is the cheapest hardwired 240V heater on this site, and 30A is far more likely to fit an existing garage subpanel than 40A is.

7,500W draws roughly 31 amps and typically wants a 40A circuit with 8 AWG copper. The Dr. Infrared DR-975 is the one to buy at this wattage precisely because it publishes that gauge, and because it switches between 4,700W and 7,500W — so you can run it at the lower setting on a milder day instead of cycling the full load.

Neither ships with a cord. Hardwired means a junction box, conduit and a licensed electrician, full stop. Ranked picks at both wattages are in the best electric garage heaters.

The exception worth knowing about: the NEMA 14-50 plug

One heater here sidesteps the electrician entirely, if you are lucky with your garage.

The InoKraft 7,500W unit ships with an 8.2 ft cord terminating in a NEMA 14-50P plug. That is the 50-amp receptacle used for RV hookups, many EV chargers and some welders. If your garage already has one — and a surprising number built or upgraded in the last decade do — this heater is a plug-in install at 7,500 watts, with a digital thermostat spanning 40 to 99F and a 1-24 hour timer.

Two caveats. If the outlet does not already exist, installing a 50A receptacle costs roughly what hardwiring the same heater costs, so the advantage evaporates. And using the EV charger's outlet for the heater means unplugging the car.

Checking your panel in five minutes

1. Open the panel door and read the main breaker. It will say 100, 150 or 200 amps. That is the whole house's budget.
2. Count free slots. A 240V heater needs two adjacent empty slots for a double-pole breaker. Two single-slot gaps in different places will not do.
3. Look at what is already there. Electric range, electric dryer, electric water heater and an EV charger are the big consumers. A house with all four on a 100A panel has no room for a 40A heater and needs a service upgrade first.
4. Note the distance from panel to garage. Run length drives conductor size and therefore cost. A detached garage 80 feet away is a different job from an attached one sharing a wall.

Take those four facts to an electrician and you will get an accurate quote on the first call. If the answer is that the panel will not take it, gas becomes the sensible route — electric versus gas garage heaters works through that fork, and garage heater running costs covers what each one costs to run afterwards.

The heaters at each electrical tier

Once the electrical question is settled, size the heater to the garage rather than to the circuit — the garage heater sizing guide has the square-footage arithmetic, and it is worth doing before you commit to a wattage. For a standard insulated two-bay garage, the two-car garage page covers heating alongside the lighting and storage it shares a budget with.