How Many Sq Ft Will an 80,000 BTU Garage Heater Heat?

How much garage it heats

Coverage depends on two things: how well the garage holds heat and how much warmer than outside you want it. The table uses an 8 ft ceiling. For a 10 ft ceiling, multiply the area by 0.8.

Which garages it fits

Each garage below is at 20°F outside and 60°F inside, average insulation unless noted.

An 80,000 BTU heater covers a 24 × 24 two-car garage at average insulation, with 161% to spare. The 2-car garage heater size guide compares 20 × 20 and 24 × 24 garages in BTU and watts, and the garage heater BTU chart lists every common size.

• 2-car, 24 × 24 ft, poor insulation, 20°F outside: needs 37,000 BTU/hr (10,800 W). This heater covers it.
• 3-car, 32 × 24 ft, average insulation, 20°F outside: needs 32,500 BTU/hr (9,500 W). This heater covers it.

Bigger or smaller?

Before buying this size for a house garage, check whether insulation or door seals would let a 50,000 or 60,000 BTU unit do the job. It is the right call for big detached garages, shops with roll-up doors and spaces with 12 ft ceilings. When the need passes its 64,000 BTU/hr of output, as a 30 × 40 shop with a 12 ft ceiling does, look at 100,000 BTU or two smaller units.

Mr. Heater 80,000 BTU Big Maxx

The heater most people mean by a Mr. Heater 80,000 BTU is the Big Maxx MHU80, a vented natural gas unit heater that hangs from the ceiling. Mr. Heater's manual rates it at 80,000 BTU/hr input and 64,000 BTU/hr output, 80% efficient. That is the same output this page uses, so the coverage table above applies to it.

Mr. Heater says it “heats up to 2,667 sq. ft.” Our model gives about 1,500 sq ft at average insulation and a 40°F rise, and 2,000 sq ft with good insulation. The maker's figure lines up with a well-insulated garage held only 30°F above outside, about 2,670 sq ft in our model.

• In a home garage, the manual says the bottom of the heater must be at least 8 ft above the floor.
• It runs on 120 V and draws 2.3 A.
• It vents through a 4 inch pipe. A horizontal residential run is 5 to 25 ft plus one 90° elbow, sloped up ¼ inch per foot.
• It ships for natural gas with a propane conversion kit.
• It runs at full input up to 2,000 ft. From 2,000 to 4,500 ft the manual lowers the manifold pressure.

Mr. Heater also sells a portable 80,000 BTU forced-air kerosene heater and an 80,000 BTU propane convection heater. Both are unvented, so their exhaust stays in the space they heat; check the propane heater indoor safety check before running one in a closed garage. We have not tested these heaters, and this page has no affiliate links.

Gas use and running cost

Gas heaters are rated by input. At full fire this one burns about 0.80 therms of natural gas or 0.87 gallons of propane an hour. That costs about $1.18 or $2.23 an hour at 2025 average prices.

Over a month of 6-hour days with the heater running half the time, plan on about $107 on natural gas or $201 on propane. Put your own rate and hours into the cost to run a garage heater calculator.

Other gas heater sizes

• 30,000 BTU
• 50,000 BTU
• 60,000 BTU
• 80,000 BTU