Before anything else: have you sealed the door?
We are going to keep saying this, because it changes the answer to every question below. If you can see daylight under or beside your closed garage door, buying a heater is buying a machine to warm your driveway. Spend $30 on a seal first. The heater you then need will be smaller, cheaper to buy and much cheaper to run.
The three questions that decide this purchase
1. What electrical supply do you actually have?
This is the question the box does not answer and the reviews rarely mention. Every genuinely capable electric shop heater runs on 240 volts. The Dr. Infrared DR-988A, for instance, publishes 4,800 W at 208 V or 5,600 W at 240 V, and it ships with a NEMA 6-30P plug — which needs a dedicated 30-amp 240-volt outlet. Most domestic garages do not have one, and running one is an electrician’s visit that frequently costs more than the heater.
On an ordinary 120-volt outlet you are capped at about 1,500 W by the circuit, which is roughly 5,100 BTU/hr. That is enough to take the edge off a small, sealed, insulated single garage. It is not enough to heat a cold two-car space, and no amount of marketing changes the arithmetic.
2. What will it cost you per hour?
Nobody in this category publishes this, which is odd for a purchase that is entirely about money. It is a one-line calculation.
Cost per hour, for any electric heater
Cost per hour = watts ÷ 1000 × your rate per kWh
A 5,600 W heater is 5.6 kW. At the U.S. average residential price of 18.34 cents per kWh (EIA Electric Power Monthly, June 2026), that is 5.6 × 0.1834 = $1.03 per hour at full output. A thermostat cycling at roughly half duty makes it about 51 cents. Two hours a day across a 120-day winter is $123 to $246.
A 1,500 W plug-in heater, by the same sum: 1.5 × 0.1834 = 28 cents per hour. Much cheaper, and much less heat.
Put your own electricity rate into the heater calculator — the national average is a starting point, not your bill. The full running-cost comparison across heater types is here.
3. Electric or combustion?
Propane heaters sidestep the electrical problem completely, which is why they are popular in garages, and they bring two things worth understanding before you buy rather than after.
Burning propane produces water. In a space where the whole objective is keeping metal dry, adding moisture to the air is working against yourself. And every propane heater manual publishes a minimum fresh-air ventilation requirement, which works directly against the sealing you just paid for. Mr. Heater publishes low-oxygen and tip-over shutoffs as standard on its portable range, and those are real safety features — but they are protections against the hazard, not an argument that the hazard is not there. Read the ventilation section of the manual for your specific model before you decide, not after it arrives.
Skip this
Skip the 'garage heater' that is a 1,500 W space heater in a metal box
Search results in this category are full of them. A 1,500 W heater is a 1,500 W heater regardless of the roll cage around it and regardless of whether the listing says “heats up to 1,000 square feet”. That claim is not a specification and it is not derived from one. Work out the wattage you need from the volume and the temperature rise, then buy something that delivers it.
What size do you actually need?
Not what the box says. Volume × temperature rise × 0.133 × an air-change factor. For a sealed, partially insulated two-car garage at 24 × 22 × 9 feet, going from 20 F outside to 55 F inside, that is roughly 22,100 BTU/hr, or about 6,500 W — which is why the honest answer for most two-car garages is a 240-volt unit and a conversation with an electrician.
Change any of those inputs and the answer moves a lot. Target 45 F instead of 55 F and the requirement drops by nearly a third. That is a real decision worth making deliberately, and it is exactly what the calculator is for.
