It's a contraption most of us know little about but rely heavily upon. It’s your trusty furnace, and it’s fairly complex, involving electricity, natural gas or heating oil, water, steam or forced air and an exhaust vent.

With all that, there's plenty that can go wrong.

While furnaces are typically reliable — many newer models can detect when something is amiss and shut off automatically — they aren’t without risk. And when problems happen, the results can be devastating.

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What can go wrong?

The most dangerous elements of a furnace involve the fuel coming in and the exhaust going out. Here’s what can happen:

A fuel leak. If you have a gas furnace and you smell gas in your home, get out of the house immediately. It's not time to do an inspection on your own. The simple act of flipping on a light switch or operating anything electric could trigger an explosion, according to Connecticut’s Department of Energy and Environmental Protection. As soon as you get out of the house, call the fire department and the gas company.

A carbon monoxide leak. Because most furnaces involve burning fuel to generate heat, they generate carbon monoxide. That deadly, odorless gas is supposed to vent harmlessly out of your house. But a furnace — particularly an older one — can develop cracks that allow the gas to escape into your house. Problems with the furnace’s venting system can also cause the gas to leak inside your home.

Install at least one carbon monoxide alarm on each floor of your home. The Consumer Product Safety Commission (CSPC) recommends placing them away from heating vents and appliances that burn fuel. Don’t put one in your kitchen, they advise.

Fire and explosion. In order to make your whole house warm, a furnace has to generate very high temperatures. And remember, it also may be burning fuel. Those high temperatures combined with fuel bring the possibility of fire, so store combustibles like paint thinners and gasoline away from your furnace, the Air-Conditioning, Heating, and Refrigeration Institute (AHRI) advises.

Excessive heat buildup. If you have forced hot air heating, do not close more than one-fifth of the registers at any one time when the heat is on, the AHRI says. (Registers are the covers at the end of the air ducts that deliver air to a room. They typically have levers on them that allow you to adjust the air flow.) Closing them too far can cause excessive amounts of heat to build up in the furnace.

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Keep your furnace as problem-free as possible

Follow these steps to make sure your furnace can keep doing its job safely.

1. Shut it down when the heating season is over. Follow the manual or contact your heating contractor for what should be a very simple step of disabling your furnace for the summer. That should prevent anything from going wrong when it's not in use.

2. Vacuum around the furnace to keep lint and other items that can burn from accumulating, the AHRI recommends.

3. Change the filter in your furnace at least three times a year, if your furnace uses a filter, the AHRI says. Read the manual, contact the manufacturer or ask a heating professional to find out if your furnace has a filter. A clean filter will help your furnace burn fuel more efficiently.

4. Have a heating contractor perform annual maintenance on your furnace to be sure it's running as efficiently as possible and that there are no problems. Issues homeowners might encounter include clogged filters that stifle air flow, cracks in the combustion chamber that leak carbon monoxide, faulty thermostats and ignition switches that don't operate properly. The professional will also check the electrical components. (Whether your furnace burns oil or natural gas, it also typically involves an electrical component connected to the thermostat so that the unit fires up when needed and turns off when it's not.)

5. Watch for oil leaks near the tank, if you have an oil-fueled furnace. Oil-fueled furnaces require delivery of oil to a tank on site. If oil spills during delivery or from cracks in your furnace, follow these directions from the Wisconsin Department of Health Services for how to clean it up properly.

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Mitch Lipka is a consumer columnist and product safety expert. He was the 2011 recipient of the "Kids Best Friend Award" from Kids In Danger for his commitment to reporting on children’s product safety.