The weather is getting colder, and in Maine that means homeowners across the state are firing up their wood stoves.

After a summer without the homey smells wood stoves produce, in mid- and late-fall it’s comforting to come back to the traditional home heating system of wood burning.

But if your stove equipment is not up to snuff, it could be emitting an excessive amount of particulate matter — the soot and smoke emitted from wood stoves that linger in the air — which can have negative effects on people’s lung health.

“That really can affect air quality dramatically,” Dr. Marguerite Pennoyer, a Scarborough-based asthma specialist, said.

While all wood stoves emit some level of particulate matter, the largest producers are older wood stoves that were manufactured before the U.S. Environmental Protection Agency began placing standards on wood stoves in the 1980s.

Since wood stoves last as long as replacement parts can be purchased for them, these older models are still lingering in many Maine households, according to Trevor Sleight, service manager for Evergreen Home and Hearth in Brewer.

“Some [stoves] people have been burning for years, they love it. They want nothing else, and that’s all they can have,” Sleight said. “They’ll last as long as you can get parts for them. There are many out there that are the pre-EPA.”

To help people afford to replace their non-EPA certified wood stoves, the American Lung Association of the Northeast sponsors a program where people living in select program locations can qualify for a voucher that will go toward purchasing a new EPA-certified wood stove to replace their non-EPA certified wood stove. The pilot program started in May 2015 and has had great success, according to Michelle Edwards, a coordinator of health promotion and public policy for the American Lung Association of the Northeast in Maine.

“We are people who hang onto our wood stoves in Maine. We are resilient,” Edwards said. The American Lung Association is “just trying to ensure that people are burning as efficiently and cleanly as they can.”

When it launched, the Maine voucher program covered residents in the Rumford River Valley communities of Andover, Byron, Canton, Carthage, Dixfield, Hanover, Peru, Mexico, Roxbury and Rumford. This fall, the program expanded to include the towns of Farmington and Wilton.

The Lung Association of the Northeast also sponsors a changeout voucher program in Rockingham County, New Hampshire. The individual programs are funded by settlements or fines paid by organizations or individuals who violated air quality regulations, Edwards said, and the settlements determine where geographically the funding can be put to use.

The pilot program in Maine had a funding of $41,000 when it began in 2015. With 39 $1,000 vouchers having been given out since the program started, only two $1,000 vouchers remain. The American Lung Association of the Northeast expects that the funding for this program will be exhausted by the end of the year, effectively ending the voucher program in that area.

Each changeout program that the American Lung Association of the Northeast facilitates is funded from different settlements that dictate where the voucher programs can be implemented, but Edwards said they are hopeful they will be able to expand elsewhere in Maine next year.

“The people who get the $1,000 are so appreciative because it’s a win all around,” Edwards said. “It’s a win for the retailer, the voucher recipient, and it’s great for the Lung Association because it helps us attain some of our air quality.”

Wood stoves of the pre-EPA certification era could emit up to 70 grams per hour of particulates, according to Sleight, compared with the average 3 grams per hour of particulates emitted by modern wood stoves.

The particulates emitted by wood stoves, both outside and inside a home, can have detrimental health effects that expand beyond impacting lung health and triggering asthma attacks, Pennoyer said, adding that exposure to particulates also can impact the heart.

Pennoyer recommends that anyone with asthma should steer clear of having a wood stove in their home. For those who rely on the hearth for a primary or secondary heat source, she urges that they use an EPA-certified stove.

“These older stoves, the ones that you can see right through the seams are not great,” Pennoyer said. “More efficient stoves are better.”

The EPA regulations target the burning systems of the stove, the level of particulates being emitted from the stove, and the amount of heat being emitted from the physical body of the stove, Sleight said. To cut down on particulate emissions, modern stoves may feature catalytic converters or secondary burn systems, which injects air below as well as above the fire so the smoke at the top of the fire box is also being burned — minimizing the amount of particulates released from the stove.

“The newer EPA-certified stoves are more efficient; therefore, you’re getting more out of your wood and putting less into the environment,” Sleight said.

Sleight said about 30 to 40 percent of his customers are looking to replace their wood stove that they have been burning with for a long time. While people can find non-EPA certified stoves online, Sleight said he always recommends that people purchase EPA certified stoves and keep them well-maintained by using proper burning habits as outlined in the manufacturer’s guidelines.

Pennoyer said people often don’t realize that wood stoves can impact health because they have become such a winter custom.

“There’s nothing nicer than a wood stove going in a home,” Pennoyer said. “If it’s well maintained and efficient, it’s wonderful.”