The burner may have to be cleaned or adjusted, or the chimney and vents may need to be inspected for possible blockage. Try the Thermostat. Hold your hand under the vent hood. See your owner's manual to locate the vent hood. If you notice hot air backing out of the vent hood, turn off the furnace and call your local heating contractor or Wisconsin Electric.
Hot air can mean blockage in the vent or chimney.
Inspect the Vent and Flue Pipes. Look for rust or rotted-out areas which could allow combustion fumes to escape into your home. Learn about Carbon Monoxide dangers. Squeeze the Flue Pipes. Wear an oven mitt.