When the price of crude oil increased sevenfold between 1973 and 1980, many homeowners wondered how they would heat their homes if costs continued to climb. That’s when heating with a wood (both logs and pellets), long harnessed as a home-heating fuel in the far north, began to sound like a good idea for the rest of the nation.
Fast-forward 35 years. Wood stove heaters are once again a popular choice for many cash-strapped homeowners. Despite oil’s most recent surge in price, however, wood heat’s resurgence is somewhat surprising. This is, after all, the era of clean, green energy typified by wind, solar and geothermal power. Wood heat has long suffered a reputation for being dirty and unsafe.
Not anymore. The improvement of wood-burning appliances is an industry success story. New wood stoves are 30 percent more efficient than old ones, wresting between 70 percent and 80 percent of the heating potential from every log. And they’re much cleaner-burning as well. At worst, a new EPA-certified stove produces less than 7.5 grams of particulate per hour (g/hr) compared with the 40 to 60 g/hr of older wood stoves. Many models do better than that, producing only 1 or 2 g/hr. If you burn sustainably harvested firewood, you won’t be contributing to global warming at all. That’s because the CO2 emissions that remain are absorbed by new tree growth at roughly the same rate as the emissions are produced.
Radiation or convection?
Today’s clean-burning wood stoves (including fireplace inserts and hearth stoves) achieve high levels of combustion with a super-hot, stone-lined firebox and prewarmed combustion air that’s introduced at the top of the firebox from small holes. Just about everything gets burned. They are safer, too: Cleaner burning reduces the likelihood of chimney fires, along with the frequency of chimney cleaning.
If you’re heading to a wood stove showroom soon, you’ll need to decide what fuel you want to burn and whether to buy a stove that gives off heat primarily via convection or radiation. In general, radiant-heat stoves are better for when you want to heat one floor of a house that has an open plan. Radiant heat travels in straight lines and heats objects, not the air. Convection stoves, often fan-assisted, heat the air, which then circulates from room to room and up open stairwells. These stoves are better for homes with several floors and divided spaces.
Most stoves perform best when burning seasoned hardwood logs. Pellet-burning stoves, however, are making big inroads. These stoves burn pellets made from compressed sawdust. The pellets automatically drop into a small, cup-shaped grate (models that load from the top are preferable) and burn with a fury — so much so that there’s barely any ash to clean out later. Another benefit: You may not have to install a long flue through the roof or up the side of the house; pellet stoves, like high-efficiency gas furnaces, can often be vented through an exterior wall. One drawback is that pellet stoves don’t work when the power is out; they rely on electricity to feed both fuel and air to the burn chamber as well as to operate the thermostat.
The heat-storing fireplace (also called a masonry heater or masonry stove) is another very efficient wood burner that’s gained popularity during the past few decades. It’s different from a steel or cast-iron wood stove in two important ways: 1) Its fires are relatively short and very hot, and 2) it’s built of a ton or more of stone (usually soapstone) that can store large amounts of heat (photo 1).
Operation of a masonry stove is straightforward. First, build a blazing fire in the combustion chamber. Let it burn for a couple of hours, heating the stone mass. Channels built into the fireplace help to circulate the hot gases, allowing the stone to soak in most of the heat. Then you close the damper and walk away. The stored heat will radiate from the fireplace’s stone mass for as long as 24 hours. Compare that with the heat from a charge of wood in a typical metal stove, which lasts only six or seven hours. Not only do you spend less time building and tending fires, but you have greater peace of mind when you leave your home with the fire out but the heat still “on.” In addition, the radiant heat of a masonry stove tends to be more comfortable and even than the convective heat of metal stoves. And the surface of masonry heaters is typically warm but not hot to the touch, so there are no worries about kids’ burning their fingers.
Some wood-heat experts argue that masonry stoves are not appropriate for regions with moderate climates. Others say they’re fine for climates as far south as North Carolina and that you don’t need to build a large fire to warm these stoves enough for them to radiate heat. A moderate fire, occasionally stoked with a few logs, will allow you to control heat output even when all you want to do is to take the chill and dampness out of the air.
The big downside of masonry heaters is cost. Once you add up the cost of the unit, installation, venting system and structural improvements to support the stove’s weight, a price tag of $30,000 would not be uncommon. Smaller, far less expensive steel stoves sometimes incorporate stone panels, but they aren’t massive enough to store the large amounts of heat that most homes require.
Joseph Provey, a veteran woodburner, is a freelance writer living in Bridgeport, Connecticut.