What Size Heater for a 1-Car Garage?
A typical 12 × 20 ft one-car garage with an 8 ft ceiling needs about 10,000 BTU/hr, or 2,900 W of electric heat, at average insulation and a 40°F temperature rise. A 4,000 or 5,000 W heater on a 240 V circuit covers most one-car garages. A 1,500 W plug-in heater usually does not.
One-car garage heater sizes
The rows below cover the usual range of one-car garages and winters. Find the one closest to yours, or change the numbers in the calculator above.
| Scenario | Size | Insulation | Rise | Heat needed | Electric | Gas input |
|---|---|---|---|---|---|---|
| Typical, mild winter | 12 × 20 × 8 ft | Average | 30°F | 7,500 BTU/hr | 2,200 W | 30,000 BTU/hr |
| Typical, cold winter | 12 × 20 × 8 ft | Average | 40°F | 10,000 BTU/hr | 2,900 W | 30,000 BTU/hr |
| Typical, very cold winter | 12 × 20 × 8 ft | Average | 50°F | 13,000 BTU/hr | 3,800 W | 30,000 BTU/hr |
| Deep or oversized, cold winter | 14 × 22 × 8 ft | Average | 40°F | 13,000 BTU/hr | 3,800 W | 30,000 BTU/hr |
| Well insulated, cold winter | 12 × 20 × 8 ft | Good | 40°F | 7,500 BTU/hr | 2,200 W | 30,000 BTU/hr |
Can a 120 V plug-in heater heat a one-car garage?
A 1,500 W plug-in heater makes about 5,118 BTU/hr. In a 12 × 20 garage with average insulation, that holds the space only about 20°F above the outdoor temperature. With good insulation it manages about 26°F. On a 25°F morning, that is a cold garage.
Where a plug-in heater shines is spot heat: aimed at you at the bench, it feels warmer than the air around it. Plug it straight into a wall outlet, not an extension cord, keep it 3 feet from anything that can burn, and do not share that circuit with other big loads. The electric garage heater guide covers 120 V versus 240 V in more detail.
One-car garages are electric-heater territory
Most one-car estimates land between 7,500 and 15,000 BTU/hr, which is 2,200 to 4,400 watts. That is comfortably inside what a single 240 V electric garage heater delivers, so a 4,000 or 5,000 W unit covers most one-car garages without gas lines or venting.
Size for the coldest weather you actually get, then buy the next standard capacity up. A 13,000 BTU/hr requirement becomes a 15,000 BTU/hr unit. One size up is fine. More than about twice the requirement wastes money and makes the heater cycle on and off.
Attached and detached garages behave differently
An attached garage often shares one or two walls with a heated house, so its real heat loss is lower than the same structure standing alone. A detached garage is exposed on every side and usually runs a step colder. An attached, partly finished garage may honestly rate good insulation, while the identical detached one rates average or worse.
“One-car” also covers everything from a tight 10 × 18 bay to a deep 14 × 24 space. Measure length, width and ceiling height before you buy. It takes two minutes and removes the biggest source of error.
One-car garage heater questions
How many BTU do I need to heat a 1-car garage?
About 10,000 BTU/hr for a 12 x 20 x 8 ft garage with average insulation and a 40°F temperature rise. Good insulation brings it down to about 7,500 BTU/hr.
Will a 1,500 watt heater heat a one-car garage?
Only in mild weather. A 1,500 W heater makes about 5,118 BTU/hr, which holds a 12 x 20 x 8 ft garage about 20°F above outside at average insulation, or 26°F with good insulation. It is better at warming the spot where you work. Read the electric garage heater guide.
What size electric heater for a 1-car garage?
About 2,900 W for the typical 12 x 20 garage at a 40°F rise, so a 4,000 W or 5,000 W 240 V heater covers most one-car garages with room to spare. See what a 5,000 W heater covers.