I have a gas furnace with forced hot air. The system runs for 5 minutes and then turns off even when the temp is still several degrees lower then what is set on the thermostat. After about 10 seconds the furnace starts up again and runs another 5 minutes then shuts off again. It will do this until the room temp equals what is set on the thermostat. The guy who installed said this is normal, but seems very inefficient. It is a Rheem system, 80 efficiency rating.

Might be a air flow problem. Pull the filter out and see if it run's normally.