What Size Heater for a 2-Car Garage?

Two-car garage heater sizes

These rows cover compact and full-size two-car garages across mild to very cold winters. The highlighted row is the most common case.

What size electric heater for a 2-car garage?

For a full 24 × 24 garage at average insulation, plan on about 7,200 W. A 7,500 W heater on a dedicated 240 V circuit covers it, usually on a 40 A breaker in the 125% example. A compact 20 × 20 garage needs about 5,000 W, which a 5,000 W heater covers.

Electric reaches its limit quickly in this size class. A very cold winter (a 50°F rise) pushes the 24 × 24 garage to 8,900 W, and poor insulation pushes it to 10,800 W, which takes 2 heaters on separate circuits. At that point a gas or propane unit heater usually wins on running cost and wiring, or insulation brings the load back into one-heater range.

A 120 V plug-in heater is not a whole-garage answer here. At 1,500 W it supplies about a fifth of what a 24 × 24 garage needs on a cold day. The electric garage heater guide explains circuits and running cost.

Why 20 × 20 and 24 × 24 need different heaters

Adding four feet to both sides sounds minor, but 24 × 24 × 8 holds 4,608 cubic feet against 3,200 for a 20 × 20: 44% more air to heat. That is the difference between a 20,000 and a 25,000 BTU/hr class unit. Tandem and storage-heavy layouts stretch further still, which is why the car count alone can put you a full size off.

From required BTU to a heater you can buy

The 24 x 24 x 8 ft example requires 24,500 BTU/hr output, about 7,200 W electric. At 80% efficiency, the smallest input class in our comparison that meets this estimate is 45,000 BTU/hr. Confirm actual manufacturer output and circuit or venting requirements before buying.

With the same dimensions and 40°F rise but poor insulation, the requirement becomes 37,000 BTU/hr. These are modeled examples, not field measurements. A larger door, higher ceiling, or longer warm-up may require a more detailed heat-loss assessment.

What if you have a single-car garage?

A 12 x 20 x 8 ft single garage needs about 10,000 BTU/hr and 2,900 W under the same average-insulation, 40°F-rise assumptions. One-car size does not automatically mean a 1,500 W plug-in heater is enough. Measure first, then compare the 1-car garage heater size guide.

Use the running-cost estimate for this load and installation budget after checking size.

Garage doors are the weak point

Two overhead doors can be a quarter of the wall area. Uninsulated steel doors with tired seals leak heat faster than any wall, so judge the insulation setting by the whole enclosure, doors included. In our model, insulated doors cut the default 24 × 24 garage from 24,500 to 21,000 BTU/hr. Try it in the garage heater calculator with Compare an upgrade.

Size for how you use the space, too. A workshop held at 60°F every day and a garage warmed to 50°F for weekend projects are different jobs. Enter the temperature you actually want.