Don't wait until it's cold outside to check your gas furnace. Here's what you can do right now.
Press and hold the pilot control knob to start the pilot.
Make sure the flame is well-formed and blue.
Natural or propane gas from an outside source is piped to the furnace where it is burned to produce heat. Usually a fan-driven forced-air distribution system blows the warmed air through ducts that vent into the various rooms of the house. Older gas furnaces use a standing-pilot ignition. Maintenance involves turning off the pilot each spring and relighting it each fall. Newer, more efficient gas furnaces use an electric spark to light the gas as necessary.
To light the pilot on a standing-pilot (always on) ignition system, follow the lighting instructions located near the control. Here are the typical steps:
Light the pilot:
Set the control knob to the pilot position. Hold a long match under the pilot gas port.
Press the control knob; the pilot should light. Hold the control knob down until the flame is burning brightly (about 30 seconds). Release pressure on the knob, and turn it to the on position.
Adjust the pilot:
Remove any cap covering the pilot adjusting screw on a combination control.
Turn the adjusting screw counterclockwise to increase the flame or clockwise to decrease it. It is correctly adjusted when the flame envelops the thermocouple bulb by 1/2 inch and appears dark blue with a small yellow tip.
Adjust an adjustable burner air shutter:
Set the thermostat to its highest setting to keep the burner running. Once the furnace has heated up, remove the burner access panel and loosen the locking screw.
Open the shutter by turning it to the right until the blue base of the flame appears to lift slightly from the burner port surface. Then close the shutter until the flame reseats itself on the surface.