Hey Michael,
Temperature was just below freezing with blowing snow and fog. After the initial warm up at medium setting we had the 2KW heater run on low setting for most of the evening. At one point it got way too hot and we opened the windows about half way for quite some time without feeling cold at all. Durring that time we had zero condensation on the windows. We turned the heat off at night, but the windows about 1" open. At that time we got condensation build up on the open windows. Not much you can do about it, just simple physics. It wasn't a big deal as the water was dripping out into the open. Once we turned the heater back on in the morning the condensation was gone in no time. Even though the had a good cross flow of fresh air at night, we never felt cold. I was only using a summer duvet and wearing short sleeve.