So far I have not yet ever turned on my furnace. All of my camping with my travel trailer has been during summer weather, usually with the a/c going non-stop as soon as I plug into shore power at an RV park. I know that my trailer's water and holding tanks are not insulated and I would not attempt to go camping once it goes below freezing, but I wonder how cold I should expect to be able to handle using the trailer forced air furnace? I'm guessing that I would be OK to about 40 degrees outside temperature, but doubt that the little furnace could keep us comfortable much below that. What do you do?