When I was a child, we had a system.

If you needed to use the outhouse — really use it, the kind that takes time — you turned on the electric heater five minutes before you went. Ten if you had the patience. The outhouse was cold, especially in winter, and the electricity cost money, so you didn't just leave the heater running all day. You planned. You waited for someone else to finish, then went immediately after, while the air was still warm.