This post is the unedited version of an article I wrote for Fine HomeBuilding magazine which appeared in the December 2021/January 2022 issue. My original version was more focused on garage designs for heating dominated climates, FHB helped to make the article relatable to other climates. The link will bring you to the printed version. FHB304-ConditioninganAttachedGarage.pdf (finehomebuilding.com)
I consider the attached, heated garage a luxury item. I used to have one, it was nice not having to scrape ice or clean snow off my vehicles. Having a warm car when its below zero outside was also nice. But I was paying for that luxury, around $100 per month for energy costs in December, January, and February. There was also the added cost of the heating equipment and extra insulation needed when building the space. And lastly, there was always moisture in the space, both in liquid and vapor that needed to be dealt with.