I live in Canada where it isn’t considered a cold day if the temperature is above 0° (-18° celsius for us). My shop is in an attached garage but it doesn’t have its own door to the house. I have to go outside and then in through a back door.
When I decided to convert it to a workshop it was very important to me that I be able to use all 12 months of the year. This includes our hot summers where it goes into the 90’s or the cold winters where it regularly drops below zero. The first step I did before buying anything was to insulate the three exterior walls and ceiling. I was lucky that the garage had a window so to keep it cool in the summer all it took was a window air conditioner. This was very successful all summer.
My bigger concern was winter. My house doesn’t have natural gas so I had to decide how I wanted to heat it. For this first year I decided I try out a portable 240V, 5500 watt heater I bought from Lowes. I had it wired in direclty to my panel and had a switch installed in my basement. I normally keep it turned off and keep the garage at about 40° using a small 110V heater. Because of the garage being insulated and having the one shared wall with the house I find the garage easily stays at this temperature.
When I’m ready to work I go downstairs and turn on my big electrical heater. Within an hour the shop usually goes from 40° to 60° in an hour and gets to 70° in about an hour and half. Perfect timing to have dinner and relax a bit before heading into the shop. When I’m done work and head back inside I flip back off the heat.
I find the big cement slab of the floor and all the tools act as excellent stabilizing heat sinks. I found this particularly helpful in the summer.
So far it’s worked out great. I’m always able to use my shop, even on the coldest days, the electric bills are reasonable and its not unnecessarily heated when I’m not using it. I think I’lll stick with this setup.