We have no gas lines in the house, but we just started to have a strong smell of gas in only one bedroom which comes and goes maybe 1x a week, for 6 hrs or even 2-3days. We cannot use the bedroom. Smell goes away very fast, seem like being pumped in, if something is on, then off. Its not the air unit, it does not smell in the bathroom next to the bedroom,and not in the walk in closet which shares a wall. Gas was not detected when gas company came in and the smell was quite strong then. The intensity of smell varies

This could be a faulty wax seal or a low level in one of the traps. Your nose will be the best detector in this case. Where's the smell the strongest? Is it worse at night or colder weather? Any plumbing work done lately? Let me know, Tom