Fireplaces and wood-burning stoves can provide welcome warmth and a cheerful atmosphere, but critics warn that stoves and fireplaces may also cause air pollution and may be sending wasted dollars up the chimney.

The American Lung Association of Utah warns that smoke from these devices contains carbon monoxide, hydrocarbon and other organic compounds that can cause respiratory illness and aggravate existing conditions such as bronchitis, emphysema and asthma.The association suggests that only wood that has been split and dried for six months be burned; avoid smoldering fires; never burn garbage or trash; and watch for visible smoke from the chimney or lazy flames in the firebox - which indicate that more air is needed for burning.

Traditional fireplace and wood-burning stove efficiency can range from minus 10 to plus 10 percent, says Stephen E. Poe, Utah State University Extension energy specialist. In contrast, newer more energy efficient airtight stoves can range from 30 percent to 50 percent, he said.

Poe said the wide range in efficiencies are a result of differences in design, maintenance and operating procedures.

"For high efficiency, a stove must do two jobs well. First, fuel must burn as completely as possible so that little smoke and unburned combustibles go out the chimney. Second, heat must be transferred from inside the stove to the room.

"The chimney must be properly sized to provide adequate draft. A sooty or dirty chimney will restrict draft and reduce combustion efficiency."

Creosote is formed from flue gases that escape from the fire and cool as heat is absorbed by the stove pipe and chimney system. Ifthe temperature of the flue gases drop below about 270 degrees, the unburned volatile gases and water vapor condense, causing creosote build-up, Poe said.

To avoid creosote deposits, Poe said it is necessary to keep the fire burning brightly. A hot-burning fire keeps the flue temperature high enough to prevent the creosote from building up prematurely. A low or smoldering fire tends to deposit more creosote.

Construction of fireplaces in new homes continues unabated, and sales of wood stoves and fireplace inserts are brisk, industry figures indicate.

One reason cited for the continued interest in wood-burning stoves is the Persian Gulf crisis, which has boosted the cost of oil, a common home-heating agent, especially in the East.

Most wood stoves are sold in the fall and early winter, but sales in August of this year - the month Iraq invaded Kuwait - were double what they were a year earlier, some retailers report.

Melvin Pace, 47, Farmington, who calls himself the Chimney Sweep Man, has made a part-time business from cleaning stoves and fireplaces.

A materials control expert at UNISYS for the past 23 years, Pace and a friend started a stove and fireplace cleaning business 10 years ago after the friend had a chimney fire. The two men decided cleaning chimneys could be both a practical and rewarding service to the community.

"My friend got out of the business after a year, but I stayed with it and have enjoyed the work and the part-time income I get," Pace said.

He is especially busy in the spring and fall, and while he dresses up as an English chimney sweep on occasion, he generally just arrives at homes in ordinary work clothes.

It takes about half an hour to an hour to completely check a wood stove and its stove pipe or a fireplace or fireplace insert and the chimney, and the cleaning chores can last much longer, depending on the difficulties involved.

Pace said anyone who uses a fireplace or wood stove regularly should have it checked at every two years. "We don't have any chimney laws in Utah, but some states require fireplaces and stoves be checked annually," he said.

Pace uses huge steel brushes attached to long steel poles to clean chimneys and stovepipes and also vacuums them with special attachments.

"I often take more than three gallons of soot and creosote out of a dirty chimney," he said.