120V Garage Heater Check
A plug-in heater is the easiest way to warm a garage, but it is small. Enter your garage to see how much of the heat loss one 1,500 W heater covers, and when you need two or a 240 V heater.
Your garage
Can a 120 V heater do it?
Only with two heaters on two circuits
Your garage needs about 10,000 BTU/hr (2,900 W) at 20°F. One 1,500 W heater covers about 51% of that, so it would hold the garage near 38°F on that night. Two heaters on separate circuits get you to 55°F.
Each heater draws about 12.5 A, most of a 15 A circuit. Plug it straight into a wall outlet, one heater per circuit, never on an extension cord or power strip.
Electric garage heater: 120 V vs 240 V →What one 1,500 W heater can do
Every 1,500 W heater makes the same 5,118 BTU/hr, whatever its shape or price: electric resistance heat turns all of its electricity into heat. That is enough for a small insulated garage or a workbench, but a typical 2-car garage loses several times that on a cold night. The tool compares the two numbers and tells you roughly what temperature one heater can hold.
A second heater only helps if it is on a different circuit, because two 1,500 W heaters on one 15 A circuit overload it. Past two, a single electric garage heater on a 240 V circuit is simpler and safer, and the garage heater wire size calculator shows the breaker and wire it needs.
Making a plug-in heater go further
Heat only where you stand: aim the heater at the bench, close the door, and seal the gaps around it. A radiant or infrared plug-in warms you and the surfaces in front of it rather than the whole air volume, which suits short sessions. Insulating the door and ceiling helps more than any heater upgrade; the garage insulation calculator shows how much.
Questions people ask
Will a 120V heater heat a garage?
A small, insulated one, sometimes. A standard 1,500 W plug-in heater makes about 5,118 BTU/hr. Our default 1-car garage, 22 × 12 ft with some insulation, needs about 10,000 BTU/hr to stay at 55°F on a 20°F night, so one heater covers about 51% of it. Bigger or colder garages need 240 V.
Can a 120V heater heat a 2-car garage?
Not in real cold. A 24 × 24 garage kept at 60°F on a 20°F night needs about 24,500 BTU/hr, which is about 5 plug-in heaters, each on its own circuit. One heater only covers about 21% of the heat loss, so use it for a workbench and a 240 V heater for the whole space.
How many amps does a 120V garage heater use?
A 1,500 W heater draws about 12.5 A at 120 V, most of a 15 A household circuit. Anything else on that circuit, such as a compressor or a shop light, can trip the breaker, so give the heater its own outlet and circuit.
Is it safe to use a plug-in heater in a garage?
It can be if you follow the basics fire services give for space heaters: plug it straight into a wall outlet, never an extension cord or power strip, keep 3 feet clear around it, and turn it off when you leave. Keep it well away from gasoline, solvents and sawdust.
What is the biggest 120V garage heater?
Most plug-in heaters stop at 1,500 W because that is about what a standard 15 A outlet can supply. Bigger electric garage heaters run on 240 V, which delivers the same watts at half the current.
Sources
Sources last checked November 7, 2026.
- Cleveland State University, Portable space heaters (undated) · 1,500 W at 12.5 A
- USFA, Heating fire safety (undated)
- Consumer Reports, Will using a space heater save you money? (Oct 12, 2025)
- DOE Energy Saver, Electric Resistance Heating (archived) (captured Jan 1, 2026)