Does the Furnace Need to Be ON?

It’s that time of year in Wisconsin that the windows can still be open during the day to have cool fresh air circulate through the house. But the nights are getting too cold to leave them open. So I play a little game at night after I close the windows where I try to guess if I need to turn the furnace on for the night. Granted there’s nothing actually stopping me from just leaving it on, but there is a small financial and environmental cost that plays in the back of my head. Is the furnace really a need tonight? I decided that tonight is a yes. And soon enough having the furnace on will be a need for several months straight. Autumn is beautiful around here but turning the furnace on and off keeps me from forgetting that there’s a cold winter just around the corner.