Gary, it sounds like the heater needs to be cleaned. Sounds like the heat exchanger is full of dirt bunny's.If you have a manual it will tell you how and what all needs cleaned. If you do not have manual i would call a heating/cooling repair company and have them come out and clean and inspect it. Then you can watch how the tech. does it then you will know how it is done if you want to do it next time. The heater should be cleaned every year they say but you might be able to go every other year