YAKIMA, Wash. — With the arrival of winter weather this week, families across the Yakima Valley are firing up the heat in their homes — but thanks to a state grant, fewer will be relying on inefficient, old wood-burning stoves.

Yakima County’s air quality is worse in the winter because air tends to get trapped in the Valley. Smoke from wood stoves can build up and contribute to elevated levels of small particle pollution, which has serious health impacts.

“The idea is we want to get those old stoves out of service,” said Dave Caprile, spokesman for the Yakima Regional Clean Air Agency, which runs a stove replacement program.

The program helps residents with the costs of swapping out their old wood stoves for cleaner options — gas or electric heat, or newer, certified wood or pellet stoves. Replacement is free for low-income homeowners, and there’s a rebate program for those who don’t qualify.

Rebates are higher for switching to gas than for a upgrading a wood stove.

From 2011-12, the program removed 203 uncertified stoves from use, according to Caprile. Most of those people switched to cleaner wood options, but about a quarter opted for gas, propane or electric heat.

Caprile said the average annual levels of particle pollution in the Valley have been decreasing since they started the replacement program and began calling more burn bans.

The limit for 24-hour average particle pollution is set at 35 micrograms per cubic meter of air. In 2009, Yakima’s annual average was 37.3, over the limit, Caprile said, but it has fallen steadily to 30.7 in 2012.

In August, the state gave Yakima a new $600,000 grant to run the replacement program for the next two years. Officials hope to swap out stoves for more than 250 families.

The state-certified wood stoves produce more than 10 times less pollution than the older models, but according to Ron Tinnemore, wood stove coordinator with the state’s Department of Ecology, it’s equally important that homeowners know how to burn cleanly.

“With wet wood or not enough air flow inside, they can produce just as much pollution as the old ones we’re replacing,” Tinnemore said.

The new grant program will run until 2015 or the money runs out, Caprile said, but this is their busy season.