I live in Ottawa, Ontario, and I have the opposite problem.(posted 9140 days ago)Try keeping your chemicals in a deep tray of water at approximately 68:F. Ditto for your developing tank, and you should be able to maintain the chosen temperature.
When I work in an unheated basement, where the air temperature is 5:C (41:F), I use a water bath of TWO degrees Farenheit ABOVE the temperature I want to maintain. Since your problem is the opposite of mine, you may want to try a water bath of two degrees LESS.
The way to test is to get your developer to exactly 68:F, and pour it into the developing tank. When development is done, catch the developer as you pour it out of the tank and check the temperature. I was starting with 68:F developer going into the tank and getting 66:F when I was done developing, hence my recommendation of two degrees more.
I can only fantasize about a darkroom which is too HOT; try dragging a 4X5 view camera, camera bag and accessories on a toboggan while you attempt to walk over the snow (but mostly through it) when the temperature is -25:C (-13:F)!