Troubleshooting a Gas Furnace

By Bob Formisano, About.com Guide

The Conventional Gas Furnace
The conventional gas furnace (up to 89% AFUE) is an appliance looking like a large box that does the following:

• takes in cold air,
• cleans it with an air filter,
• heats it up with a gas burner using a steel heat exchanger,
• distributes the warm air with a blower motor through your home's ductwork

The heated air then cools down in your home's various rooms and returns to the furnace through return air grills and ductwork.The cold returning air enters back through the air filter into the furnace to complete another heating loop.
Sometimes there is a humidifier mounted on the furnace or the return air ductwork.
Furnaces come in different efficiencies measured in AFUE.
Once in a while things don't work quite right and you need to troubleshoot a gas furnace repair or relight a standing pilot if it has one. Conventional furnaces may have electronic ignitions which need special troubleshooting.

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