HAMPDEN, Mass. (AP) _ Rob and Lynne Wallace jumped at the chance to install an outdoor wood boiler two years ago to heat their home and water supply.

For a year, they were immune to fluctuating fuel oil prices. Their family-owned tree service provided more than enough wood, stacked under a canopy near the furnace about 50 paces from their back patio.

But earlier this year, their small western Massachusetts town set limits on the outdoor boilers that forced the Wallaces to shut theirs down.

Concerned about air quality and neighborhood disputes, Hampden joined a growing number of communities nationwide setting their own rules on the increasingly popular wood boilers, which are not federally regulated. The U.S. Environmental Protection Agency recommends emissions and air quality standards, but does not regulate where and when the wood-fired burners can be installed or used.

Rules are patchy on the state level, too.

Some states, including Connecticut and Maine, have regulations and let their municipalities adopt even stricter limits or ban the boilers altogether. Massachusetts has considered statewide rules but has not enacted them, while Michigan offers a model ordinance that local governments can adopt in the absence of statewide standards.

The Northeast States for Coordinated Air Use Management, a government coalition, estimates more than 155,000 wood boilers have been sold since 1990 in the Northeast, upper Midwest states and other areas prone to cold winters.

For those with easy access to wood, the boilers could make their homes among the few that are not vulnerable to swings in fuel oil and natural gas prices.

A recent Energy Department report says the cost of natural gas, used by 58 percent of American households, could rise 10 percent this winter. Heating oil, used by 7 percent of the country's homes, could jump 22 percent. Those who use electricity and propane will also see increases, with the prices of those sources estimated to rise 4 percent and 16 percent, respectively, this winter.

The Wallaces and others say wood boilers are an economical heat source that uses a renewable resource rather than dwindling foreign fuels.

``We're not hillbillies or trashy people. We're educated people who did our homework before we made our purchase, and we made it a point to operate it very conscientiously,'' said Lynne Wallace, whose unit would comply with the new town rules only if they spend thousands to move it elsewhere on their land.

The boilers resemble small sheds and burn wood to heat water, which is piped underground to the nearby home or other structure to provide heat and hot water. Some owners also use them for hot tubs, greenhouses and businesses such as dairy barns.

Depending on their size, their purchase price can range from about $5,000 to $15,000. That does not include pouring the foundation on which they sit, installing underground piping, extending the unit's smoke stack to exceed the height of any nearby roof, and other costs.

Their proliferation has prompted disputes over where they can be operated, the amount and smell of smoke emitted and other neighborhood issues. Many of those conflicts are being played out in town meetings and the offices of selectmen, mayors and health boards.

``You don't realize what you're dealing with until you get this haze all around your house and your back yard,'' said Chris Anderson, who bought his home in East Longmeadow, Mass., last year before learning that his neighbor had one of the boilers.

That 13-square-mile town, surrounded on all sides by communities with limits on the units, is considering its own rules. Emotions have been running high, however, about whether the limits should include existing units _ as in neighboring Hampden _ or apply only to newly installed boilers.

``My wife and I saved up for our dream house and this is the biggest investment of my life, and we can't enjoy it,'' Anderson said. ``I'm not saying they should be banned everywhere, if they're put up in a good place away from other houses, but why should we be smoked out?''

Advocates of the boilers say irresponsible users _ those who burn trash, chemically treated wood and other unacceptable substances _ are ruining it for others who stick to the clean, seasoned wood recommended by manufacturers.

``We beg our customers to extend their chimneys higher up so the smoke disperses where their neighbors aren't affected, and we beg our customers to burn only the right wood,'' said Scott Bradley, owner of Mainline Heating & Supply of Ashford, Conn.

``We tell them you have the right to use a wood burner and stop using foreign oil, but you never have the right to smoke out your neighbor,'' he said.

In an attempt to avert such problems, Connecticut requires the boilers to be at least 200 feet from the nearest home not served by the unit, and also mandates chimney heights and the quality of the wood to be burned.

But those rules apply only to burners installed after July 2005, and towns can set stricter regulations or refuse to ``grandfather in'' older units if they wish. Some communities have banned the outdoor boilers altogether, including several in western Massachusetts and the eastern Connecticut towns of Hebron and Tolland.

Robert Girard, assistant director of the Connecticut Department of Environmental Protection's air enforcement division, said the department urges potential buyers to research whether their site is suitable before they make the purchase.

``Sometimes they're just not put in the right place because of the topography, the closeness of neighbors, things like that,'' he said. ``There have been a number of cases where people have had to remove the units after they've spent a lot of money to put them in.''

The Wallace family, which has returned to oil heat for their Hampden home, is still pondering what to do about the wood-fired boiler that sits cold and empty outside their house.

``It would have paid for itself in a few years,'' Lynne Wallace said, peering into the unit's firebox on a chilly recent morning. ``And here it sits, off.''

(Copyright 2007 by The Associated Press. All Rights Reserved.)