I have a masonry lined (firebrick) fireplace that was originally made to burn wood and the previous owner converted it to accept a vent free log set. I called the manufacturer of the insert and they confirmed it would take a vent free log set. I have a 24" vent free log set and I'm not happy with the heat output. Even with the flu closed I went outside and could see plenty of heat escaping the top of the chimney (35 feet above the insert) The snow that was on top today melted in about 10 minutes and now I can see heat radiating from the chimney. Is that from the insert getting hot and heating the air in the flu? It's really putting out a lot of super hot air at the top. Is normal? It does still seem to heat up the space but very slowly and never get really warm. There is a fan below the insert that I run that blows a small amount of air from the top of the insert. Please help.