When I was garage door shopping for the new place, there are some pretty crazy insulation options you can get for a garage door, but they get expensive pretty quick. My doors are R10, but you can get garage doors with like R20. I don't entirely believe that any more is any better...given that garage doors have air leakage around the entire perimeter pretty much. If you have any windows on your doors, that also impacts the insulation. I opted for Insulated Glass on my doors, not sure what the R value is, but it was an option so I went with it, it's dual pane glass. I personally will have hydronic heating in my garage as I have the pex pipes inside of my slab, but only plan on keeping it like 5-10 degree.....I can't imagine anyone running higher than that, seems wasteful personally, but to each their own.This quote is hidden because you are ignoring this member. Show Quote
At my current house, my detached garage is unheated, but it is insulated, with an insulated builder grade door (don't know R value), but just that alone is enough to keep the garage at -9.5% when it was -38 outside. I don't understand how it stays so warm personally, guessing the heat from the hot engine of the car. At -10 car obviously starts no problem, but one night I went to the Renovation Show downtown when it was like -32 outside and parked my car at the train station outside for 5 hours....she struggled and then sounded like it was going to explode for a good 5 min until it warmed up, also could drive more than like 20km/h as everything was so resistive.
I guess my point in all of this is, you don't really need to heat the garage if your plan is to simply have a car that isn't a frozen block of ice every morning, just having it insulated might be enough. If you plan on working in there frequently than that's a different topic, but for general car storage, it's not really needed. I have a small electric heater I can turn on to bring up the temp a bit if I am in there, but I hardly ever use it, electric heat is so inefficient and expensive. I personally think radiant heat, via a radiant heater or slab heat is the best option. Some people run furnaces in their garages which just freeze right back up as you open the garage door and let all that heat out, whereas radiant will maintain warms due to it's nature of warming the things in your garage, and not just the air.