Where I live it could be 70 degrees one day and 18 and blowing snow the next. Somedays I let my firebox go totally cold. Should I leave an ash layer or just clean it out when it goes cold? My next "question" is more of an observation. When the house is cool and a new fire is started I get the feeling of humidity as the house starts to heat. I was wondering if someone knows the physics of why that happens? it does not last for long only an hour or two and I don't see a rise on my humidity gauge.