There are two types of natural gas heaters to consider for heating your garage: a forced-air garage heater that blows warm air like a conventional furnace, and a “low intensity” infrared tube heater that radiates heat. (Avoid “high-intensity” infrared heaters—which visibly glow red—because most aren't approved for residential use.) Both will burn natural gas (your most economical choice) or LP gas, and both are available in several sizes, so you can choose the one that best heats your space. Both require an electrical hook-up, and both require venting to the outside as well. But the similarities of the two types end there (see chart).
Make sure your garage walls and ceiling are insulated (minimum of 4 in. thick in the walls, 6 in. thick in the ceiling); otherwise you'll waste energy and money. The basic differences are how the heaters perform and how they feel in terms of comfort.
If you plan to work on projects in the garage, presumably with wood, an infrared heater may work better because it doesn't raise dust or keep dust airborne. A forced-air heater will stir up sawdust, which is a big problem when you're painting or staining.
You won't feel warm as quickly with an infrared heater because it heats objects first, then the air. However, once your concrete floor warms, you'll feel more comfortable because infrared heat is more uniform. But you must keep all objects 3 to 4 ft. away or they'll overheat—and so will you. With forced-air heat, the air is warmer at the ceiling and cooler at your feet. And a forced-air heater will take longer to reheat the space after the garage door has been opened and shut.
Another big difference is the initial cost. Most forced-air units cost half as much as low-intensity infrared tube heaters. We paid $611 (not including the vent kit and thermostat) for the 60,000-Btu Modine Hot Dawg forced-air unit, and $995 (including the vent kit) for the 30,000-Btu Caribe infrared unit shown. However, it's usually less expensive to run the infrared unit, so the cost difference will decrease with frequent use. Check with the manufacturers or a local heating pro for a more exact estimate.
Installation is markedly different too. Infrared heaters must be installed a minimum of 7 ft. above the floor, and must hang down a minimum of 4 in. from the ceiling (check the manufacturer's instructions, as these measurements vary with the size of the heater). It's critical that you make sure objects below are not too close. The 30,000 Btu unit shown requires a minimum 3-ft.distance from heater to objects below. Most infrared heaters are installed at the back of a garage pointed toward the garage door, then aimed downward at a 45-degree angle. They can also be installed between car bays if the garage door opener rail allows and you don't have a tall vehicle.
With a forced-air heater, the installation details aren't as exacting. Most are placed in a corner, near a gas line and an electrical outlet (needed to power the blower). The instructions will indicate the exact spacing required between the unit and the sidewalls or ceiling.
How many Btu you need depends on variables such as the garage size, your climate zone and the temperature you want to work in. A basic rule of thumb for forced-air heaters is 45,000 Btu to heat a two- to 2-1/2 car garage, and 60,000 for a three-car garage. The makers of low-intensity infrared tube heaters say that 30,000 Btu can heat a two to 2-1/2 car garage, and suggest 50,000 for a three-car garage. Check with a local heating pro or the heater manufacturer for a specific recommendation to fit your needs.
Both heater types need to be vented if powered by natural gas or LP gas. Check the instructions for specific vent pipe sizes and lengths (some models include a vent kit, or you can purchase components separately). Most can be routed either through sidewalls or through the attic and roof.
One other option, if venting or gas-powered heat isn't what you want, is an electric infrared heater. Granted, electric heat may cost you more to run, but check with your local electrical utility to see if it offers any type of rebate or off-peak rates that would make this option more cost efficient.
Forced-air verses infrared
- Less expensive initial cost (50 percent less than comparable infrared heater)
- Loses heat quickly if garage door is opened (longer recovery time)
- Heat rises and stratifies (the air is warmer at ceiling, cooler near floor), but you won't notice it with a 7- or 8-ft. ceiling
- Air movement tends to blow airborne dust around (woodworkers will have to shut down unit before staining and finishing projects)
Low-intensity infrared tube heater:
- Little noise
- No air movement (dust settles)
- Lower cost to operate
- More uniform heat distribution (no stratification)
- Quicker heat recovery if door is opened/closed (floor and objects retain heat)
- Higher initial cost (50 percent more than forced-air)
- Correct location of heater is critical (minimum 7 ft. from floor, 3 ft. from objects). Adequate headroom is also critical, because you can overheat if you're working near the unit.