MISSISSIPPI STATE -- Gas heaters that don't work well aren't just a cold annoyance, they can also be a health hazard.

Herb Willcutt, safety specialist with Mississippi State University's Extension Service, said malfunctioning gas heaters can kill an entire household by releasing deadly amounts of carbon monoxide. What could be prevented by regular maintenance usually takes several lives across the country each year.

"Normally, gas heaters are very reliable and efficient, but they can produce carbon monoxide when improperly cleaned or adjusted, and they could ignite nearby objects if the controls malfunction," Willcutt said.

Gas heaters require oxygen to mix with the fuel as it burns. When the unit is starved of oxygen because of blocked intakes or a mechanical failure, the units can produce deadly carbon monoxide. They are also inefficient as they use more fuel to produce less heat.

Carbon monoxide is deadly when breathed in sufficient quantities. Each year, many people die or are sickened by exposure to carbon monoxide from malfunctioning gas heaters. Gas heaters should be serviced annually by qualified technicians.

Servicing includes inspecting, cleaning and adjusting heating equipment. Check the air intake to make sure lint and dust have not blocked the air intake.

"An untrained homeowner who tries to service a gas heater could make the problem worse by failing to clean properly, getting the air controls further out of adjustment or potentially damaging other equipment," Willcutt said.

Replace a gas heater anytime it becomes defective or cannot be cleaned or adjusted correctly.

"Service heaters annually before the heating season and anytime unusual flame characteristics or noises are noticed," Willcutt said.

He defined unusual performance as longer than normal, bright yellow flames, visible flames on radiant heaters, a pilot light that will not stay lit or noises coming from the furnace that are not normal.

"Call in a professional to perform the maintenance or repair," Willcutt said.

Increased efficiency is an added benefit of having the heater unit serviced.

"Normally these units are very reliable and efficient," Willcutt said. "Far greater dangers exist from homeowners who use supplemental heaters or place combustible materials too close to heaters."