I’ve known many a wood stove. For most of my childhood in Maine, there was the gray-enamel Glenwood, a maternal mountain of silver curlicues and cast-iron hinges. Peggy the basset hound invariably got stuck when she plowed under the skirt to bake her brains on a winter’s day.
During the oil embargo, a little Jotul airtight joined the family. We kids were warned repeatedly not to leave the draft wide open, for fear of melting it off its skinny black legs. In a later house, there was a hulking airtight that looked like office-lobby sculpture.
Those were the wild and woolly days of wood heat. With three demonically curious kids in the household, you can bet many, many things besides nicely aged oak and pine suffered trial by fire: Junk mail, beef bones, egg shells and cereal boxes were routinely crammed in; hair clippings and plastic were especially entertaining. We even tried firing clay pottery among the gasping flames.
But the wood stove, once a symbol of back-to-nature self-sufficiency, now stands accused of causing cancer, urban smog, respiratory problems, even global warming. Wood burning is now considered one of the most polluting methods of home heating.
All of Colorado is now covered by wood-burning legislation, as are parts of California and many other states in the Rockies and Pacific Northwest.
Carbon monoxide, inhalable particulates, hydrocarbons, formaldehyde-this is just a mouthful of the 100-plus compounds that waft from a chunk of burning wood. This cocktail may smell wonderful, but beware the hangover. Carbon monoxide slows your thinking, perception and reflexes and accelerates the onset of angina. Hydrocarbons, particularly benzene, cause cancer. Formaldehyde causes eye and respiratory problems as well as cancer. Nitrogen dioxide and sulfur dioxide are respiratory agitators, and polycyclic organic matter is another cancer-causer.
Pre-adolescent children are especially vulnerable to this onslaught of indoor-air pollution. Studies have shown that kids from wood-burning homes have higher rates of respiratory illness than kids from fossil-fuel homes-their still-developing lungs are more vulnerable to pollutants. But elderly people, smokers and those who already have a respiratory or heart condition are also more likely to suffer from wood smoke.
Of course, most of the smoke goes outdoors. In areas where winter inversions of warmer air layers trap cooler air near the ground, wood smoke contributes to very unhealthy outdoor conditions. One study by the federal Environmental Protection Agency concluded that inhaling wood smoke on a high-pollution day is the same as smoking 16 cigarettes.
While the toxics listed above are undesirable, particulates are a more complex problem. “Particulates” is a general term that covers little bits of almost anything-dust, carbon, ash-that floats around in the air. A particle of dust may also carry toxic chemical hitchhikers. Inhalable particulates are the worst, as they can lodge in your lungs. From there, depending on their chemical characteristics, they may make forays into the body to cause cancer or other biological mutations.
Toward a better burn
Wood is dirty because it’s tough to destroy it completely. A fair amount-perhaps 20 percent-of the energy potential in wood takes the form of gases that won’t burn at less than 1,100 degrees Fahrenheit. So in the average stove, where the firebox reaches a temperature of only 800 degrees, all the nasty compounds we met earlier simply go up the chimney. Rather than capturing the heat stored in those compounds, you and the neighbors inhale them.
But as the EPA has cracked down on wood-burning appliances, technology has risen to the occasion. The new generation of cleaner stoves falls into two families: catalytic and non-cat (or high-tech) stoves.
Catalytic stoves take their inspiration from Detroit. Just as the catalytic converter in your auto allows petroleum fumes to burn at a lower temperature, the catalyst in a new stove lets smoke burn at about 500 degrees. The metal-coated catalyst stands between the firebox and the chimney. Smoke is incinerated as it passes through.
Ideally, a catalytic stove will come with a thermometer, which will help you operate it efficiently. For one thing, if the fire is too cool, smoke will clog the catalyst instead of burning. The catalyst should be bypassed until the thermometer indicates that the fire is up to speed. Second, a thermometer that struggles to reach 1,000 degrees may be the only way you can tell if your catalyst needs to be cleaned or replaced.
If you’re an old hand with wood stoves, take note that a catalytic stove should be bigger than your old “low-tech” stove, and be prepared to sacrifice the responsiveness of older stoves. Thanks to the draft-deadening catalyst, it will burn more slowly and deliberately, throwing less heat.
“Non-cat” stoves depend on extra airflow and insulation to raise the firebox temperature to smoke-destroying levels. Non-cats put the art back in stove operation. While the non-cats have a much more complicated air path than the old stoves, they are almost as responsive. On the other hand, because they’re designed to run hot and only hot, they require smaller loads of wood and more of them. It’s generally easier to get eight hours of heat from a loaded catalytic stove than a non-cat.
Which stove is cleaner? The EPA allows catalytic stoves to emit 4.1 grams per hour of particulates, and non-cats 7.5 grams. However, non-cats are expected to burn consistently over their lifetime, while the ability of a catalyst to burn smoke drops over the course of its lifetime. (Federal regulations require catalysts to be guaranteed for at least six years.) Catalytic stoves are also generally more efficient-they deliver more of the heat stored in wood than do non-cats.
Put another pellet on
Pellet stoves are a new technology even cleaner than catalytic stoves. Pellet stoves run on processed wood waste that looks like rabbit food. Stored in a hopper inside the stove, the pellets are fed to the firebox by an auger. Many stoves can be left alone for days. The fuel is much drier than wood, so it burns more cleanly. This means you may be able to get away with a pipe through the wall instead of a chimney to exhaust gases.
Pellet stoves are also convenient: The fuel comes in handy 40- to 60-pound bags, there’s minimal ash to deal with and certainly no wood to split and haul. But there are downside considerations if you’re intrigued by this new technology:
– Where’s the closest pellet manufacturer? Pellet makers tend to be clustered in the Northwest, and the farther you are from there, the more you’re going to pay for fuel.
– If you’re going to depend on it for whole-house heating, you’ll get chilly during power outages; pellet stoves need electricity to run fans and the feeding auger.
– Economically speaking, pellets are “marginal at best and extravagant at worst,” admitted Dan Melcon, a member of the board of directors of the Association of Pellet Fuel Industries. Melcon, in an article written for the stove industry, calculates that pellet stoves are two or three times as expensive to run as wood stoves.
– The EPA has determined pellet stoves average a 78 percent transfer of stored energy to room warmth. A division of the Department of Energy tested four stoves and found average efficiency in the range of 54 percent.
– Pellet stoves are self-feeding, but they’re not self-cleaning: You still need to shovel out the ash. They’re more complicated than wood stoves and require more maintenance.
The irony of gas
While gas is the undisputed champion of clean combustion, the prospect of drawing a rocking chair close and gazing at the blue rings leaves something to be desired. Thanks to lifelike ceramic logs, fake glowing embers and “flame picture” improvements, the new generation of gas stoves and fireplaces makes gas an appealing option.
Gas comes into your home automatically-no splitting, hauling, sweeping up or ashes. Stoves are cool enough to stand 6 inches from a wall, and many models can be vented through the wall.
The irony with gas fireplaces and stoves is this: You’ll only want one if you’re hooked up to gas, and if you’re hooked up to gas, you probably already have a gas furnace that’s 95 percent efficient. It might have that pretty, yellow flame, but gas fireplaces or stoves deliver a measly 60 to 75 percent efficiency.
One of the most elegant answers is an old, European solution. Masonry stoves are gargantuan installations of stone, brick, soapstone or concrete. Many of the common designs stand human-high or taller and weigh a ton or two. This mass, riddled inside with smoke tunnels, soaks up the heat of a small, hot fire, then releases it slowly the rest of the day. Tom Stroud, who builds these heaters in Washington, fires his every evening for an hour and a half. When he goes to bed, the house is 72 degrees. In the morning it’s 74 degrees, and the temperature inches down two degrees over the course of the day.
Because the fire is so hot-2,000 degrees isn’t unusual-pollution is minimal. Alas, the masonry stove requires a solid foundation, both of cinder block and cash. Mason Steve Busch, of Buckfield, Maine, has installed $3,000 prefab units, but he also specializes in handmade, custom-designed heaters that may run to $20,000. Such an installation may incorporate a baking oven, cooktop, water heater, wood boxes and heated benches.
Do it right
If you yearn to burn, you should do several things to reduce your inevitable impact:
– Insulate your house so that it requires less wood to heat. Arrange your winter days around the sunny rooms.
– Burn well-seasoned, dry wood in small, hot fires.
– Regularly check your stove for cracks, crumbling gaskets and fractured firebrick.
– Avoid burning treated and painted woods, as they may contain toxic compounds.
– Avoid burning papers other than black-and-white newsprint-others are likely to contain clay coating, metals and other additives that will not only choke your catalyst but also pollute the air.
– And put on a sweater.
Heat sources
For a list of EPA-certified woodstoves, including addresses, write: Wood Heater Program (EN-341 W), U.S. Environmental Protection Agency, 401 M St. SW, Washington, D.C. 20460; phone 703-308-8688.
For brochures titled “Combustion Appliances and Indoor Air” and “Catalytic (or Non-Catalytic) Woodstoves Installation, Operation and Maintenance,” write: Public Information Center, U.S. EPA (PM-211 B), 401 M St. SW, Washington, D.C. 20460.
Some manufacturers:
– Vermont Castings Inc., Box 501, Route 107, Bethel, Vt. 05032; 802-234-2300. Range of fuels.
– Jotul, 400 Riverside St., Portland, Maine 04104; 207-797-5912. Wide range of fuels.
– Heat-N-Glo Fireplace Products Inc., 6665 West Highway 13, Savage, Minn. 55378; 612-890-8367. Gas and wood stoves.
– Buck Stove Corp., Box 69, Spruce Pine, N.C. 28777; 800-438-2825. Wide range of fuels.
– EarthStove Marketing Inc., 10595 SW Manhasset, Tualatin, Ore. 97062; 503-692-3991. Wide range of fuels.
– Stoveworks Inc., 1 Branch St., Medford, N.J. 08055; 800-STAY-WARM
