We got a new 95% efficient forced air natural gas furnace installed in June 2010. We used it for the first time during the winter of 2010. After it ran for a few weeks, I began to smell gas every time the heat kicked on. I called the gas company out, and the man found no leaks. He had the heat turned up to 70 (we keep it at 63), and he smelled no gas. So I figured everything was fine. So we went through the whole winter without any problems. We have just recently turned our furnace on for this winter, and once again I am smelling gas every time the heat is on. There have been times when I come home from work, and when I open the door, all I can smell is gas. What can be causing this? If it was a leak, wouldn't I smell it all the time?