If I already have natural gas heat, would I save money by using a direct vent gas insert? When I go to stores to ask this question, I don't really get a straight answer; guess they are all interested in just selling the gas insert. But if you already have natural gas heat, is the direct vent gas insert more efficient than a natural gas furnace? Also, I noticed that the Mendota D-40 has a BTU range from 6500 - 40000 BTU's. Isn't it better to get an insert that has a wide range like this? The room where the insert would be is about 16X20. Mendota is the only one I have found so far that has this wide of a BTU range. Thanks for any comments.