State officials are preparing to launch a buy-back program aimed at removing outdoor wood boilers that are causing persistent air pollution problems for downwind neighbors.

Earlier this year, the Maine Department of Environmental Protection enacted new rules regulating the emissions of new outdoor wood boilers sold in the state. The new rules also set minimum setback requirements and smokestack height standards to reduce conflicts with neighboring property owners.

Now, the DEP is proposing a buy-back program that would target the most problematic boilers that have been deemed a nuisance or that pose a threat to public health or safety. The Board of Environmental Protection is expected to hold a public hearing on the issue next month — likely on Oct. 16 — and is soliciting feedback on the plan.

Ron Severance with the DEP’s Bureau of Air Quality said the boilers must have been installed before February 2008.

Additionally, homeowners first must exhaust all potential remedies to be eligible for up to $10,000 in replacement funds. Those steps include increasing the smokestack height or setback distances from neighboring structures and exploring potential retrofits to fix the emissions issues.

The DEP also will maintain a list that ranks problem boilers by the level of threat they have to public health or safety, and the boilers’ proximity to neighbors or sensitive populations.

“Rather than having them apply, we would go to number one on the list and make them an offer” to participate in the program, Severance said. That will allow the department to target the most serious cases first and then move as far down the list as money allows, Severance said.

State lawmakers directed the DEP to create the buy-back program in legislation passed earlier this year but did not fund it. A portion of the anticipated funding will come from violators of the state’s environmental laws who agree to deposit money into the program as part of their fines. Another source could be the state’s general fund.

Outdoor wood boilers, also known as outdoor wood-fired hydronic heaters, have surged in popularity in recent years as property owners explore cheaper alternatives to heating oil or propane.

The furnaces are housed in small, shedlike buildings that pump hot water through underground pipes to a nearby home or structure for use as hot water or in heating systems. Boilers often can operate all day on just one or two loads of seasoned firewood, thanks to a feature that allows the owner to “damper down” the unit by reducing oxygen flow.

But that feature allows smoke and creosote to build up on the walls of the firebox. The pollutants then are released out of the smokestack when the fire is reinvigorated.

The DEP has received dozens of complaints in recent years from people who claim a boiler on a nearby property is filling their homes, businesses or even schools with potentially harmful smoke. Boiler owners and manufacturers say the contraptions generate about as much smoke and soot as many modern indoor wood stoves when properly operated and maintained.

The rules enacted earlier this year prohibit dealers from selling boilers that emit more than 0.6 pounds of particulate matter per million British thermal units, or Btu, contained in the wood fuel. The emissions level would drop to 0.32 pounds of particulate matter, or soot, per million Btu in April 2010.

Louis Fontaine, who heads the DEP’s air quality inspections program, said the department has seen an increase in complaints filed this summer because more people are using the boilers for hot water.

“We’ve found the biggest problem is people burning wet wood,” Fontaine said. “When you burn wet wood, you are using more of that wood to burn off the moisture.”

Edward Miller, chief executive officer of the American Lung Association of Maine, said the number of complaints his office hears has dropped off. Miller said some of that decline might be due to the seasonal use of the boilers or to the fact that more people are taking their concerns directly to the DEP.

His organization supports the buy-back program for the most problematic boilers.

“There really are no villains here,” Miller said. “People didn’t buy these with the intention to endanger their neighbors.”