When it's cold, we put an electric ceramic heater in the side tent, open zip down the panel in the side tent that exposes the screen, open the window in the teardrop door covered by the side tent, and open the vent in the roof of the teardrop. The heater warms up the side tent and flows through the teardrop and out the roof vent. Our porta-potty is also in the side tent, so you stay warm for those late night nature calls.