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Best way to heat a three-car garage in Zone 7

the74impala | Posted in Mechanicals on

Looking at options before I close in the walls of the garage. About 900 sq feet, 10 foot ceiling. Currently looking at blown cellulose in ceiling, 2×4 walls filled with paper faced fiberglass. 

I am not going to live in there.  I will probably avoid being out there in -30°F temps, but I would like to be half way comfortable if I need to work on a car during the winter. 

I have already purchased a Panasonic bath fan to run based on humidity. I don’t want to heat all the time and increase the speed my vehicles rot out. 

I can use the bath fan in a bath if someone can point me to a better option. 

For fuel, I could go natural gas, electric or propane could be used if needed. 

A mini split would be cool, but I don’t need a/c to speak of, and heat pumps seem insufficient in single digit weather. 

Please help. 


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  1. CraigRo | | #1

    Where in zone 7 are you located?
    If you're in the gas belt of Alaska, NG is 1/5 the price of any other energy source, makes a big difference on your wallet.
    If not Alaska, every other state (Canada excluded as I don't know there) electric rates are highly competitive with gas, and a great transition from fossil fuels.
    Others may have good comments on best construction, but I'd go with min R35 walls, R60 ceiling to reduce the heating load. Pay attention to the type of doors you use and air sealing between panels and at edges to combat air leakage. Moisture management will be important if snow melt isn't drained away. Heated slab is a good way to melt snow, drains to carry it away.

  2. Expert Member
    Peter Engle | | #2

    If you're only occasionally heating it, a unitary heater is probably going to be your best bet, powered by gas if you're in a cheap gas area. This is very low-tech and not particularly "green," but it's also very low cost. With only occasional use, it's going to be hard to justify much more than that on an operating cost basis. Plus, these heaters are designed for use in this environment. Your insulation plan is fine for occasional use. The more you expect to use it, the more that insulation will pay back. Yes to good drainage and air sealing.
    I'm not sure what you think the bath fan will do for you. It will force unconditioned outside air to enter the garage. In your area that probably means very cold air in winter and warm/humid air in summer. Either way, probably not what you want. If you want to avoid mold/corrosion in summer, a dehumidifier is probably the way to go. In winter, that's not as much of a problem.

    1. charlie_sullivan | | #5

      Agreed. Both on going with a low-cost heater and choosing a dehumidifier rather than a bath fan.

  3. Jon_R | | #3

    For very rare use, +1 on doing whatever is cheapest.

  4. walta100 | | #4

    Help me understand why you want to heat the garage. I do not see the point the car is a hunk of steel it has no feeling. It does not matter much to the car it is -40 or +40° while it is parked. I am sure that it would be a luxury to get in a car that was 80° warmer but at what cost.

    How many ten of thousands of dollars are you willing spend for that luxury instead of starting the car remotely 10 minutes earlier?

    If you must do it understand that the gas heater that are over 80% efficient collect water inside them and would likely be damaged should that water freeze. If you go high efficiency it would be best to keep the garage at or above 45°.

    If you just need to heat the garage a few times a year to work in the garage I say get a natural gas unit heater that is 80% and 200K BTUs


  5. the74impala | | #6

    Lotz of great information. I am in Northern Wisconsin. Energy isn't particularly cheap.

    Just to clarify some ideas. I might want to warm it up one warming a week, max, so I could get it to 40ish to tear a car apart. Then the next weekend, put it back together. Not too much luxury.

    I appreciate the dehumidifier option also, much more like being outside, with almost no humidity at all. Plus it will warm things up on a miniscule level.

    So if only a once a week, go <80% has, big btu, humidifier. I could add r10 of eps over the fglass in the walls. I plan to get heavy in the ceiling already. It has a single drain opening in the floor, I think I will look at making it a channel to collect from a larger area too.

    Thanks for all the good ideas.

  6. Expert Member
    BILL WICHERS | | #7

    Electricity is absolutely NOT competitive with natural gas where natural gas is available. Natural gas is almost always going to be MUCH cheaper for heating compared to electric resistance heat.

    A garage with occasional heating needs isn’t a good fit for a mini split or most heat pumps. Mini splits especially work best when they can run continually at a relatively low power level, keeping up with heat loss to keep you comfy. In a garage with occasional heat needs, you want something that can bring the temperature up relatively quickly from something pretty cold — heat pumps aren’t a good fit for this application.

    A natural gas unit heater is probably your best bet, and will likely also be the cheapest to install and probably also to operate in your particular application. Don’t use a ventless type, use one that vents to the outside. I’ve had good luck with the Modine “hot dawg” heaters that are made specifically for heating garages. They are reliable and inexpensive. Modine makes other unit heaters too and they’re aren’t the only manufacturer out there.


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