Pellet Stoves Provide a Heating Alternative
By Ray Kamada
Wood pellet stoves may be practical home heating options for many areas of the United States. Wood pellets are usually cheaper than electricity, propane, or fuel oil. They're more convenient, fuel-efficient, and burn cleaner than hardwood, but aren't quite as “green” as propane or natural gas. Pellet stove prices are comparable to other types of central furnaces but they do require more maintenance.
I was asked about pellet stoves recently, an option I'd ignored for years, due to drawbacks like maintenance. But with rising home heating costs, they're worth another look.
Pellet stoves cost from $1,800 on up. They demand more labor than gas, electric, or propane furnaces, and are trickier and generally more expensive than wood stoves but comparable in cost with other types of units when used for central heating. Some styles are free standing; some are fireplace inserts. Others are designed as central furnaces. In any case, they need feeding every one to several days and the pellet bags need dry storage space. The ash pans must be cleaned about once a week and other parts, like the augur, require occasional maintenance and cleaning. However, the total labor involved falls far short of keeping a fireplace or Franklin stove well-stoked.
What are "Pellets?"
Pellets are compressed from sawdust, wood shavings, nut shells, corn kernels, or other ground up biomass. They are shaped and sized like half a finger and come in 40 lb. bags, 50 bags (1 ton) per pallet. They're usually available at large hardware stores, like Lowe’s or Home Depot. The compression drives out moisture; so the pellets burn hotter and more completely. At 8% moisture, pellet stoves burn at 75-90% efficiency, compared to 60-70% for seasoned hardwood, which may be 20% water, or more if stacked outdoors.
So, though pellets may cost more per ton than hardwood, the price per effective therm (100K BTU) of heating may be lower. Pellet prices average about $210 per ton across the country but vary, depending on freight charges from the nearest pellet mill. There are about 60 mills in the U.S. currently. In Bellingham, Washington, you can buy a pallet for $134 because it's only 35 miles across the border from the Abbotsford pellet mill. This makes it cheaper there than natural gas or hardwood.
How do Pellet Stoves Work?
A thermostatically-controlled augur—a corkscrew that turns inside a cylindrical housing—feeds pellets from a large hopper, where you empty the bags into a small combustion chamber. With blown air, the pellets burn really hot and produce a lot less ash, creosote, and fine smoke than wood logs do. So, they're more fuel-efficient and better for your lungs and the environment. A heat exchanger extracts the heat to warm the room air intake to about 250 degrees. Another fan blows this back into the room or into a central air duct. A 3-in. diameter flue is usually sufficient to vent the exhaust gas.
Since it warms by convection, not radiant heat, and there's a steel, inner lining, the exterior surface may even be cool enough to touch. So, it's safer than a Franklin wood stove or fireplace. This usually makes a chimney unnecessary. The top-fed units may even be a little safer than the bottom-fed type because there's less chance of burn back to the hopper. However, top feeders are also more likely to choke on residual ash. Premium grade pellets leave less ash but cost a lot more.
Pros and Cons
Instinctively, there's nothing as soothing as a log fire. But after 7 winters hauling firewood, for me, the romance is long gone. Pellets are a lot less hassle. The 40 lb. bags are manageable and occupy 1/3 the space of stacked wood. Pellets are also way cheaper than propane or electric heating. Still, you need a pickup to haul 2-4 pallets for the winter. A local dealer would charge $50 to deliver a pallet to my home 10 miles away. Unlike wood stoves, pellet stoves also have a lot of moving parts that can go bad, especially with poor quality pellets that don't burn completely, leaving clinkers that gum up the augur, combustion chamber, and exhaust system.
Though wood products generally contain less sulphur than coal or fuel oil, propane and natural gas actually burn cleaner than pellets because they emit little or no smoke. Pellet stoves do tend to emit far less smoke overall than hardwood, but smaller (<0.3 micron) particles. The tiniest ones penetrate most deeply into our lungs. So, the exhaust ducting should be sealed tightly and vented properly. Better filters might help. Meanwhile, if your electricity goes out, the pellet stove's fire will also. Electric baseboard and furnace heaters have essentially the same problem. However, a pellet stove with a thermoelectric attachment will make its own electricity; they're more costly, of course.
Green Compared to What?
The claim that wood pellets add no more carbon dioxide for global warming than their natural decay is misleading because pellets burned over a single winter might take years to decay naturally. On the other hand, claims that electricity is environmentally clean are also displaced—by the length of the transmission lines from the coal, oil, gas, or nuclear-fired power plants that supply it.
For example, the giant Moss Landing plant in Monterey, California, burned mostly at night with the offshore breezes, as approved by the California Air Resources Board. However, this just meant that the bad stuff drifted a bit south before the next afternoon's sea breeze blew it back onshore. And don't forget that transmission losses dissipate typically around 40% of the power plant's energy. On top of that, any process that converts low-grade heat to high-grade electrical energy and back again is so thermodynamically wasteful that it seems silly. Yet, it's woven into our infrastructure; foreign oil dependence is another topic altogether. So, unless your electricity comes from natural gas, dams, or better yet, wind turbines, wood pellet stoves may be less polluting overall than pure electric heating.
Would I consider a pellet stove? Yes, certainly for back-up heat or maybe as a propane alternative beyond city utilities. Closer to town, the trade-offs become cost versus convenience versus a modest amount of neighborhood smoke. You should also take a hard look at the costs of different heating options because they can differ a lot, depending on where you live.