Every house Susan Moch and her husband, Roland Poirier, have owned during their 40 years of marriage has had a fireplace.

But fireplaces are notorious for wasting energy because the heat escapes through the chimney.

Moch and Poirier’s key to maintaining energy efficiency in their Fairfield County, Conn., home is a wood-burning fireplace insert that keeps the heat in the house. Installing an insert can add another source of heat, lowering energy bills for gas or oil, for example. The insert “has a blower, and it reduces our oil bills,” says Moch, an attorney.

Adds Poirier, a retired broadcast engineer: “If you don’t have this [metal] box all this heat would go up the chimney. You want to get some of that heat back into the room to make it comfortable. It makes it cozy.”

The insert has been particularly useful this year with back-to-back snowstorms and freezing temperatures. “We love it,” Moch says. “We use it every day during the winter.”

They are not alone. As people began spending more time at home during the pandemic, the demand for comfort has grown. Beginning in the fall of 2020, fireplaces and accessories became increasingly popular. Shipments within the United States and Canada of fireplaces, free-standing wood stoves and inserts climbed to 188,000 in 2020, up from 161,000 in 2019, according to the most recent figures from the Arlington, Va.-based Hearth, Patio and Barbecue Association (HPBA).

With a 2,000-square-foot house, Moch and Poirier “only need one fireplace insert to heat the whole house,” she says.

Poirier chops his own wood. If a tree comes down or a tree needs trimming, it becomes a source of wood for their fireplace. He has a chain saw and an electric splitter.

They use maple, oak, apple wood and some ash. Sometimes they cook over the fire or roast chestnuts, Moch says. They use a grill basket. “It’s not sophisticated but it’s fun. If the power’s out, the fireplace heats the house.”

An insert is “a metal box inserted into your existing fireplace,” says John Crouch, director of public affairs for the National Fireplace Institute (NFI), a sister organization of the HPBA. “It’s a controlled combustion device. A fireplace is not controlled except by how much wood you use.”

With an insert, you can control the amount of air to the fire and the amount of fuel — wood — you use. Inserts vary but are increasingly technologically advanced. An insert can have a vent at the top and at the bottom to control the air flow as well as a blower that can disperse the hot air from the fire. Owners “can control the air supply to the fire with the vents,” says Russ Dimmitt, education director at the Chimney Safety Institute of America (CSIA), based in Plainfield, Ind. With less oxygen, the fire burns slower and produces less heat. “You can have a longer-lasting fire.”

Costs for wood-burning inserts typically range from about $1,500 to about $3,500.

An insert creates a closed combustion chamber with 70 to 80 percent efficiency. This “means you harvest more of the heat energy that’s in the fuel [the wood] and less of it goes up the chimney,” Crouch says.

Dimmitt says an insert can “make an existing fireplace function better.”

Inserts are made of heavy cast iron or steel, and typically have a six-inch diameter insulated metal liner — a stainless steel pipe — that stretches from the top of the insert to the top of the chimney.

When considering a wood-burning insert, be sure it is the appropriate size for the space you aim to heat, according to the Energy Department. An insert that is too small will not provide adequate heat while one that is too large for the space can waste fuel and cause air pollution, the department says.

Experts emphasize the importance of having a wood-burning fireplace insert professionally installed. The NFI is a source for certified installers.

Wood-burning fireplace inserts became popular in the 1970s, at first during the oil embargo of 1973 to 1974 and again from 1979 to 1981 when there was an oil shortfall, according to the Office of the Historian of the State Department.

“The inserts from the ’70s and ’80s are not as clean-burning as the new ones,” Crouch says. “Inserts of the early ’90s are much cleaner-burning.”

An added bonus, Crouch says, is that the wood “insert doesn’t use electricity.” Thus, during a power outage, when your furnace doesn’t work, your fireplace can be “a backup source of heat.”

The Environmental Protection Agency began certifying inserts in 1988. The certification program was upgraded most recently in 2020.

Before having an insert installed, make sure your chimney is in safe working order. Even though newer inserts burn cleaner with much less buildup of the byproducts of burning wood in the chimney, experts recommend an inspection. And once it’s used on a regular basis, it’s important to get the chimney sweeped.

Burning wood can create creosote, a black substance that can build up in the chimney, and can cause a chimney fire. “A chimney fire is a potentially frightening and destructive event,” Crouch says. “Keeping the chimney clean is critical. It’s the nature of the fuel.” Wood “makes creosote, even in tiny amounts.”

Safety tips for wood-burning fireplaces

Here are some tips for keeping your wood-burning fireplace safe:

  • Have your chimney inspected once a year. The two most important things are to use dry wood and to maintain your venting system, which is your chimney, says Dimmitt of the CSIA. “A chimney needs to be inspected annually and swept, if necessary, to remove flammable deposits — creosote.”
  • Empty ashes once a week. Just because the fire appears to be out doesn’t mean it is. “Hot coals stay in those ashes for days,” Dimmitt says.
  • Use a tightly sealed metal container for hot ashes and coals. Never use a cardboard box or place it on a wooden deck, he says.
  • Keep a fire extinguisher nearby. Be sure it works.

How to use your wood-burning fireplace

When a wood insert is properly installed in your fireplace, the fire will generate little smoke, according to the EPA. For an efficient wood-burning fire:

  • Use seasoned wood: Aim for dry wood with a 20 percent moisture content as your target, says Crouch of the NPI. A moisture meter can be used to check the percentage of water in the firewood, says Dimmitt of the CSIA. Newspaper and dry kindling — sticks or twigs — can be used to start the fire. Avoid trash, plastic, cardboard and foam.
  • When to use hardwoods vs. softwoods: Hardwoods are denser and heavier than softwoods. They may take longer to ignite but tend to create “a hot, roaring fire,” according to the CSIA. Denser fuel tends to burn longer as well. Hardwoods include walnut, maple, mahogany, oak, teak, beech, hickory, cherry and ash. Softwoods include pine, cedar, redwood, spruce and Douglas fir. You can burn both hard and soft woods in your fireplace but hardwoods burn longer and tend to burn cleaner, producing less creosote, according to the CSIA. Burn hardwoods on colder days as they last longer and produce more heat than softwoods. Softwoods can be used as kindling or on days when it is not as cold.
  • Keep the insert door closed: This “reduces the emissions and controls the speed of the fire,” Crouch says. It burns slower.