No, the garage is not heated. I have a couple of electric heaters that I use when we have a really long spell of freezing hours. Also a work light I can set up. Generally, just closing it is enough to keep the temperature above freezing. Not much sunlight. The doors have high windows, but to let in much light they need to be open and then all the plants need to be where the sun shines in if they are to get much of it.
