Mine is in the study. It is one of the hottest rooms in the house, but my 26 year old sewing machine is temperamental at the best of times so leaving it set up means it is less likely to chuck a hissy fit. I am hoping to be able to replace it fairly soon though. and if I am really lucky I might even be able to get a cheap overlocker.
My sewing machine is pretty old, has never had a proper service and i thought it was on its way out. I found a guy who services machine, and got it serviced for $50 and it is back on track. If a new machine is not in your close future, a service might give it a new lease of life!