The facts on furnaces

Ahh, winter - that magical time of year when the snow falls on the plains, the frigid, arctic winds blow down from the north, and most of the American climate becomes a cold, unforgiving and lifeless void of heat. As we scrunch up our toes to avoid frostbite and cover our faces to prevent the icy breath of this frozen season from biting off the ends of our noses, we can't help but rejoice in the mystical, fanciful bliss of winter.

Yeah, right.

If you're like everyone else in the frozen ice caps of the American tundra, you're probably going to spend more time cranking up the thermostat than "rejoicing" the arrival of winter.

There are a number of steps you should take when giving your furnace the ol' once over. Cleaning is paramount at this point, but even more important is inspecting for damage and faulty equipment.

How a forced-air furnace

works

A brief explanation of how a furnace works will help you understand and appreciate the heating process and the reason you're going through all this annual maintenance.

A forced-air furnace consists of a unit that heats the air and an intricate system of ductwork that disperses the heated air throughout the house. The unit itself has four main sections - the blower chamber, the heating chamber, the return duct and the supply duct.

When the furnace's thermostat detects a decrease in temperature, the blower kicks on. This pulls cool air in through the return duct and blows it through the heating chamber, where the air is heated through the combustion of natural gas or through electrical resistance. The air is heated to 40 degrees above the thermostat's set temperature, and the blower continues pushing the air through the supply duct and into the house.

There are a variety of stimuli that can adversely affect the efficiency of this process. Dust and dirt can deposit on the fan's blades, reducing the amount of air it can pull and push. Dust will also regularly clog up the blower filter, reducing the amount of air that gets pulled into the unit. Dust combined with disuse can reduce the lubrication in the unit's various motors, causing friction heat and eventual failure.

• Replace the ventilation filter. These should be checked regularly and replaced often. If it looks a little dirty, switch it out. Using a clean, new filter will increase your furnace's efficiency and cut down on your gas or electric bill. On the other hand, a dirty filter can cause your heat exchanger to overheat, shutting down the system. Fiberglass filters should be disposed of and replaced, while electrostatic or electronic filters just need a good cleaning.

• Vacuum any dust out of the unit. Remove all covers (you might need a screwdriver or a wrench to do this) and suck up any and all dust inside the furnace. If necessary, tape a length of thin tubing onto your vacuum hose to get at hard-toreach places.

• If you're gung-ho about cleaning, you can unfasten the fan from its frame and pull it out for a good cleaning. Make sure the power switch is turned off before you attempt this. In most cases, the fan can be pulled out of the furnace far enough to clean it without disconnecting its electrical wiring.

• Lube up motor bearings and blower shaft bearings. Some old furnaces still employ the types of motors that require annual lubing, and this can be accomplished with some regular lightweight machine oil.

• If you have a natural gas furnace, check your carbon monoxide detector to make sure the batteries are still good, or have one installed. The combustion process of the natural gas creates deadly gases that your furnace's exhaust system should expel from the house. However, if something backs up the exhaust system that dangerous carbon monoxide has nowhere else to go. Make sure you install a detector somewhere near the furnace.

When to call a pro

Like it or not, you're furnace is a complex machine and, as such, is prone to breaking down occasionally. Usually the unit will display symptoms of an impending breakdown, and in the event of any of these you should call a heating and air specialist.

• Strange noises - Your furnace shouldn't make any strange popping sounds or rumblings. Call a tech for any odd noises.

• Soot deposits - When the combustion process is inefficient a fine soot will gather in your unit. This can indicate that the burners need adjusting or that your heat exchanger is damaged.

• Short cycles - A number of problems in your unit can cause it to run on very short cycles This can be caused by a faulty thermostat or an overheating heat exchanger.

• Carbon monoxide poisoning - If anyone in your household is experiencing chronic flu-like symptoms or unending headaches, get out. Call a technician and inform him of the possibility of CO poisoning. The fire department can also detect the presence of CO, and firefighters consider CO poisoning a life-threatening emergency. Don't feel reluctant to call.