as a fellow michigander i put my rack closer to the heat vent and run a space heater since my oil heater broke.. keep away from the outside walls of the house. also higher would be better since heat rises. on a desk near the vent compared to on the floor against the outside wall.

the heat lamp will raise core temp up a bit. i have a glass terrarium 12x18x18 and i glued foil over the screen(safely) leaving space for the light. and covered the glass sides and my ambient temp in there is 78 or higher without my adjusting. use a higher watt bulb but keep an eye on humidity.