I have a single-wide, 1964 United mobile home and my furnace, an old Mueller-Climatrol that I believe was the original one, needs help. It's natural gas with floor vents, smells funny and doesn't seem to be very efficient. PG&E has checked it and it doesn't seem to be dangerous, but I'm on a fixed income, so I need to make whatever I do spend on it count. Any ideas as to what's wrong with it?