We heat with wood heat, and get our wood from fallen, dead trees. It is a very inexpensive way to heat and doesn’t require the harvesting of valuable resources. Because of that, we don’t worry as much about having an airtight home. If you have ever been in a home heated with wood, you know just how cozy it can be – sometimes too cozy. So we have a pet door that inserts into the patio door frame, and never noticed just how much cold it let in, until we took it out the other day.