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Cold tools, numb fingers, and a project that waits until April — if that sounds familiar, a garage heater is the fix. But buy the wrong size and you’ll either freeze anyway or waste money heating a space that never warms up. Here’s how to size it right the first time.
The Quick Answer
A typical 2-car garage is 400–600 square feet. For most of them, you need:
- 25,000–35,000 BTU if the garage is insulated and in a cold climate
- 35,000–50,000 BTU if it’s uninsulated, detached, or has high ceilings
- In electric terms, that’s roughly a 7,500–10,000 watt 240V heater — or a 50,000 BTU gas unit heater, the most popular size for a 2-car garage
If you only remember one thing: it’s cheaper to insulate than to oversize. A well-sealed garage can cut your heater size (and your heating bill) nearly in half.
Step 1: Measure Your Garage
Multiply length × width for square footage. A standard 2-car garage is about 20×20 (400 sq ft) up to 24×24 (576 sq ft). Note your ceiling height too — a 12-foot ceiling for a lift holds a third more air than a 9-foot ceiling, and that air all has to be heated.
Step 2: Rate Your Insulation
Insulation is the single biggest factor in heater size. Use these BTU-per-square-foot figures for a cold climate:
| Insulation level | BTU per sq ft |
|---|---|
| Good — insulated walls, ceiling, and garage door | 20–30 |
| Average — insulated walls, bare ceiling or door | 30–40 |
| Poor — no insulation, drafty door | 50–60 |
In milder climates, scale those numbers down by about a third.
Step 3: Do the Math
Multiply square footage × your BTU-per-square-foot figure.
Worked example: A 24×24 garage (576 sq ft) with average insulation in a cold climate:
576 × 40 = ~23,000 BTU minimum — so a 25,000–35,000 BTU heater gives you comfortable working heat with a little headroom for the coldest days. The same garage with no insulation needs 576 × 55 = ~32,000–50,000 BTU, which is why uninsulated garages usually end up with a 50,000 BTU gas unit.
Shopping for electric? Convert with this: 1 watt = 3.41 BTU. So a 5,000W heater puts out about 17,000 BTU, a 7,500W about 25,600 BTU, and a 10,000W about 34,100 BTU.
Sizing Chart (cold climate, ~50°F temperature rise)
| Garage | Insulated | Some insulation | Uninsulated |
|---|---|---|---|
| 1-car (12×22) | ~11,000 BTU | ~14,000 BTU | ~21,000 BTU |
| 2-car (24×24, 9 ft ceiling) | ~26,000 BTU | ~35,000 BTU | ~52,000 BTU |
| 2-car (24×24, 12 ft ceiling) | ~35,000 BTU | ~46,000 BTU | ~69,000 BTU |
| 3-car (36×24) | ~43,000 BTU | ~58,000 BTU | ~86,000 BTU |
Which Type of Heater Should You Buy?
Electric forced-air (240V) — Clean, quiet, no venting, thermostat control. Cheapest to buy, most expensive to run. Best for insulated garages you use a few hours at a time. Needs a 240V circuit (30–50 amps), so budget for an electrician if you don’t have one.
Natural gas / propane unit heater — The workhorse choice. Highest heat output per dollar of fuel, ceiling-mounted and out of the way. Needs a gas line and venting, so installation costs more up front — but for an uninsulated or detached 2-car garage in a cold climate, it’s usually the only type that truly keeps up.
Portable propane (torpedo or convection) — Cheap, powerful, no installation. Loud, produces moisture and fumes, and needs ventilation and clearance from anything flammable. Fine for occasional use while you work; not a set-and-forget solution.
Infrared / radiant — Heats people and objects instead of the air, so it feels warm fast even in a drafty space. Good as spot heat over a workbench, weak as whole-garage heat.
Our Picks for a 2-Car Garage
Best gas unit heater: Mr. Heater Big Maxx MHU50 — 50,000 BTU
The default recommendation for a reason. 50,000 BTU covers a 2-car garage in all but the worst-insulated cases, it mounts to the ceiling with the included brackets, vents horizontally or vertically, and ships with a propane conversion kit if you don’t have natural gas. You’ll need a thermostat and gas hookup — many owners have an HVAC tech do the final connection.
👉 Check the price of the Big Maxx MHU50 on Amazon
Best electric option: Dr. Infrared Heater DR-988 — 5,600W / 240V
If you have a 240V outlet in the garage (or plan to add one) and your garage is reasonably insulated, this is the simple route: no gas line, no venting, built-in thermostat, and it’s portable enough to move where you’re working. At about 19,100 BTU it’s honestly sized for an insulated 1- to 2-car garage — if your Step 3 math says 30,000+ BTU, step up to a 7,500–10,000W hardwired electric unit instead.
👉 Check the price of the DR-988 on Amazon
Best budget spot heat: Mr. Heater Buddy (MH9BX) — 4,000 / 9,000 BTU
This won’t heat a whole 2-car garage — no portable this size will. What it does brilliantly is warm you and about 225 sq ft around your workbench, runs on a 1 lb propane bottle, and has an oxygen-depletion sensor and tip-over shutoff. It’s the cheapest way to make short garage sessions comfortable, and a good backup to keep in the corner.
👉 Check the price of the Mr. Heater Buddy on Amazon
5 Sizing Mistakes to Avoid
- Buying by square footage alone. Ceiling height and insulation swing the answer by 2–3×.
- Undersizing to save money. A too-small heater runs constantly and never catches up on the coldest days — the days you bought it for.
- Ignoring the garage door. An uninsulated steel door is basically a hole in your wall. A door insulation kit often pays back faster than a bigger heater — so see our garage insulation guide for the fix.
- Forgetting the electrical bill math. A 10,000W electric heater costs real money per hour to run. Fine for weekend projects; expensive as all-day heat.
- Skipping ventilation with fuel heaters. Gas and propane units need proper venting and a carbon monoxide detector in the garage. Non-negotiable.
FAQ
Can a 5,000-watt heater heat a 2-car garage?
It produces about 17,000 BTU — enough for a well-insulated 2-car garage in a moderate climate, or to take the edge off in a cold one. In a cold climate with average insulation, plan on 7,500–10,000 watts.
Is it better to oversize a garage heater?
Slightly, yes — about 10–20% over your calculated number gives you faster warm-up. Double the size is wasteful: gas units short-cycle and electric units just cost more to buy and wire.
What’s the cheapest way to heat a 2-car garage?
Per hour of heat, a natural gas unit heater is cheapest to run. Cheapest to buy and install is a portable propane heater — but you’ll pay in noise, fumes, and attention.
Should I insulate before I buy a heater?
If your garage has bare studs and an uninsulated door, yes — sealing drafts and insulating first can drop you a full heater size — start with our weatherstripping guide.
The Bottom Line
For most 2-car garages: insulated → 25,000–35,000 BTU; uninsulated or detached → a 50,000 BTU gas unit heater. Do the 30-second math in Step 3 for your own space, buy 10–20% above it, and spend whatever’s left of your budget on sealing the door. You’ll be turning wrenches in a t-shirt while it’s snowing outside.
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