Well, of course you can’t save a lot of energy by insulating the garage door. But if you have the same situation in your house like I have in mine when garage share two walls and part of the ceiling with the rest of the house you may save some energy and what is more important you can save on the garage heater!

Some people are buying expansive garage heaters just to keep temperature above freezing point. They want to get in the garage in sneakers and tee shirts and don’t freeze their a… off!
Once I’ve insulated the garage door several years ago since than I never have seen ice in the garage. For example the lowest temperature this year in southeastern Michigan was -5F (- 20.5C) and as it was a couple of puddles of water on the garage floor at night I’ve found them again in the morning!
So, if you have uninsulated garage door and adjacent garage you can do just what I did. If you afraid that this type of insulation which I used is combustible you can hire a company which will spray an insulation on your garage door.