I inspected a house today that had a gas insert fireplace. The first thing that i noticed was a whitie haze in the glass, similar to that of a broken window seal. I turned the fireplace on thinking that the heat of the flame would evaporate the moisture, but after 10 minutes or so the haze was still there. I could see the haze moving, but not burning off. Are there typically two panes of glass, and moisture got in between the two like a broken seal in a window? It was about 20 degrees this morning, and it had a metal chimney (under siding), not a side wall flue.