An Environmentalists Guide to Responsible Wood Heating
- Local air quality issues
- Appliance selection
- Wood heat system design
- Sustainable fuel
- Good operating technique
By John Gulland
A version of this article appeared in the Feb-Mar 2004 edition of Home Power Magazine
It's fair to say that wood energy is the black sheep of the renewable energy family and, of all the renewable options, it causes environmentalists the most discomfort. Mostly they worry that burning wood means cutting down precious trees for fuel and making a lot of smoke pollution. Besides, wood stoves are not as technologically sexy as glittering solar panels and whirling wind turbines. As one anti-wood burning activist was heard to say at a public meeting, "We need to look to new sources of energy, not old ones."
But wood is a conditionally renewable fuel and, as all environmentalists and alternative energy aficionados know, there aren't too many renewable options available, especially ones good at providing bulk heat in very cold weather. In practical terms, households hoping to run on renewable energy in moderate and cold climate regions will probably need to rely on wood fuel to some extent or they'll freeze.
The main gripe about wood heating is the smoke, a problem having two dimensions: the community and the neighborly. At the community level, topography and climate can conspire to trap smoke close to the ground. The pollution is visible, unpleasant and downright unhealthy, especially for children, the elderly and those with respiratory sensitivities. A different kind of problem arises when one household's wood smoke is so dense that the neighbors are driven indoors and even there the smell permeates clothes, rugs and drapes. Both problems are serious and together they give wood burning its bad name.
Clearly, the unreserved promotion of wood heating in all locations and circumstances is not environmentally acceptable. Even venturing to say something mildly positive about home heating with wood opens one to criticism in some circles.
Acknowledging, then, that heating with wood is not a good option for everyone, everywhere, how do you go about judging suitability in your particular case? Until now a guide to decision-making, or even to guide a discussion of the issue, did not exist. This article is an effort to fill that gap.
It might be useful to clear up three common myths: first, that wood heating involves simple equipment at the level of folk technology; second, that the installation of wood heating systems entails only the application of common sense; and third, that the skills needed for successful heating with wood are intuitive.
In truth, effective wood heating is neither simple, "just" common sense nor intuitive. Effective wood heating technologies are not simple and in fact it is simple wood burning equipment that makes all the smoke and is terribly inefficient. Some peoples' common sense in the absence of proven technical guidelines caused them to burn their houses down. And if anything, bad wood burning habits seem to come naturally. I've been building and maintaining wood fires every winter for thirty five years, and I'm still learning. Maybe it's intuitive for some people, but not for anyone I know.
In proposing an environmentalist's guide to wood heating, we'll need to answer four questions: First, should you even consider burning wood where you live? Second, what kind of device should you burn the wood in and how should the installation be arranged? Third, what is an appropriate source of firewood and how can you get some? And finally, how should you operate the wood heating system? Each of these is a big topic, justifying its own article, so in the interests of brevity, we'll just skim the high points.
Should you consider wood heating?
People who live downtown in a multi-story building, should forget about wood heating. Even if it were physically possible, it wouldn't be responsible. Even in detached houses, urban wood heating can be problematic.
In general, wood heating works best at the urban fringe and beyond, but even using that criteria there are limits. For example, if your nearby urban area has frequent air quality problems in winter, you might want to consider other options that have less local impact. If you're unsure about whether wood heating would be suitable where you live, consider this: if all your neighbors also decided that wood heating was a good idea, would it make your area a less pleasant or healthy place to live? If so, look for other options.
Also worth considering is the fuel supply. Wood heating is best done in a local context, so the fuel supply, in the form of standing trees, should be reasonably close to where you live. If your area is not well-forested, other heating options would be better.
So, if you don't live in a city, and your region doesn't have winter air quality problems, but is forested, then hey, wood heating might be for you.
How to select the right equipment
Many costly mistakes get made in the selection of wood heating equipment, and we need to clear up one of the most common pitfalls right away. Strictly decorative or recreational wood burning is not environmentally appropriate. Conventional fireplaces without heat recovery are inherently wasteful and polluting and don't belong in an environmentalist's home. We're dealing here with efficient, low pollution wood heating, and you can't do that with a conventional fireplace.
A word about houses. Ideally, an environmentalist shouldn't have a house that wastes energy because virtually all energy use produces environmental impacts. It is relatively easy now using standard building materials to create a snug, efficient house, the very kind that is best suited to wood heating. The most efficient form of wood heating is space heating with a wood stove, as distinct from central heating with a furnace or boiler. Ideally, the heater is located in the most lived-in part of the house, typically the central area consisting of the kitchen, living and dining rooms. This arrangement makes the space where you eat, relax and entertain the warmest in the house, while utility areas and bedrooms stay cooler. Moderately-sized energy efficient houses can be heated comfortably with a single, well-located wood stove.
Now an equally important word about chimneys. The chimney is not simply an exhaust pipe. Think of it as the engine that drives the wood heating system. Straight chimney systems provide the most reliable, maintenance-free performance, so locate the chimney directly above the stove location so the flue pipe and chimney run straight up from the stove flue collar. This arrangement produces quickly-building, strong draft, no backdrafts and much less chance of smoke roll-out when the door is opened for loading. Plus maintenance is reduced because there are no elbows for deposits to collect in. Straight-up chimney systems give the kind of performance we all want.
Getting the right heater is important and fortunately the general criteria are fairly simple. Look for anything that is certified for low emissions by the US Environmental Protection Agency (EPA). A good selection of EPA certified wood stoves, fireplace inserts and factory-built fireplaces is available. Not only will an EPA certified heater emit about ninety percent less smoke, it will deliver up to one-third higher efficiency than the old parlor stove or airtight. You'll get more heat from less wood and make less pollution in the bargain.
If you are a fan of all masonry construction, you could a consider masonry heater. These massive units cannot be EPA certified because of their design features, but have been shown to burn clean and provide efficient heating. A masonry heater is a specialized design in which a fire is burned rapidly and the heat absorbed by tons of masonry mass for gentle release over the next 12 to 24 hours.
You'll need help selecting the right heater. For stoves, inserts and fireplaces, visit as many specialty hearth retailers as you can and hear what the sales people have to say. If you are able to visit at least three, their relative competence will probably be revealed. I suggest you pick the dealer you trust first, before making the final product decision. A good dealer can offer you workable options, then it is up to you to select what you think looks the best. Because the stove, insert or fireplace will become an ever-present member of the family, you'd better like the look of it.
Minor differences in smoke emission ratings or in published efficiency figures don't really mean much, considering that your fuel and operating practices will have such a large effect on performance. Find a good dealer, listen to their advice and pick what you like, as long as it is EPA certified. Chances are good that you'll be satisfied. If a masonry heater is more to your liking (and you have some extra money you don't know what else to do with), contact a member of the Masonry Heater Association of North America. In my experience, heater builders are talented, committed individuals who could make a lot more money in some other line of work if they didn't insist on doing what they love.
How to identify environmentally appropriate firewood
Wood is considered to be a renewable fuel and almost carbon dioxide neutral because trees absorb CO2 as they grow. When trees mature and fall in the forest and decompose there, the same amount of CO2 is emitted as would be released if they were burned for heat. In heating our houses with wood, we are simply tapping into the natural carbon cycle in which CO2 flows from the atmosphere to the forest and back.
Appropriate firewood is produced using sustainable forest management practices, meaning that the integrity of the forest, including the trees, the soil and the site, is maintained and that species diversity, both plant and animal, is maintained or enhanced. While this may seem like a tall order or a utopian vision, the fact is that sustainable forestry management has been practiced for decades in thousands of private wood lots across North America. Farmers' wood lots that look the same today as they did fifty years ago are the best demonstration of good forest management practices.
In practical terms, sustainable forest management can be described as uneven age selective harvesting, involving the removal of damaged or diseased trees and the thinning of concentrated stands of single species, while leaving seed trees of all present species and some standing dead trees to provide wildlife habitat. Wood lots in farm country generally conform to this prescription. If you can get your firewood from a farmer, there is a good chance that it comes from a sustainable source.
The other major source of firewood is logging operations that produce lumber, pulp or veneer logs. In these operations there is always waste produced, such as trees that are center rotten or are damaged by road and trail building, and the top branches for which there may be no commercial market other than firewood. While these logging operations do not necessarily use sustainable methods, many do, and the damage would be done whether or not some of the waste wood is diverted as firewood.
The key to understanding sustainable forestry is to view the forest, not as a museum containing exhibits, but as a living community which, like all communities, is constantly evolving. Climate, soil quality and site characteristics vary widely, but many of the forested areas of North America are highly productive, meaning that a lot of firewood can be removed each year from each acre, while the quality of the stand and wildlife habitat are enhanced.
Those of us who heat homes with wood can do our part for sustainability by pressuring our firewood suppliers to prove that the wood they sell comes from a sustainable source. If many of their customers asked questions about sustainable forestry, firewood dealers would soon pressure their suppliers and the public will would be expressed within the firewood market.
Firewood should be cut, split and stacked in an open area in early spring to be ready to burn in the fall. Very hard woods like oak may take longer, and drying in damp maritime climates can also take longer than just the summer months.
Here is one final suggestion about sustainable firewood. Ugly wood piles that include wood from less desirable species tend to be more sustainable than perfect piles of maple or oak with regular pieces in the classic wedge shape. This is because straight lengths of these high value, slow growing species should be used for furniture, not wood heating. Ugly wood piles are created by using everything, right down to two-inch diameter sticks and including all the bent and twisted sections of the tops. Although I live in sugar maple country, my firewood is mostly white birch and poplar because I have a lot of them on my property and because they mature in less than 50 years and then fall over. I just catch them for firewood before they fall.
Regarding fuel other than firewood, don't burn it. Burning waste paper, or even worse, general household trash, produces elevated emissions of dioxin and some other nasty toxic gases. Burning salt water driftwood has the same result. Burn clean, dry, uncoated, untreated wood and just enough newspaper to light the fires.
What day-to-day practices produce less smoke and higher efficiency?
There is no simple formula for building and maintaining fires that deliver maximum heating efficiency and don't smoke, except to say that wood should be actively flaming until it is reduced to charcoal. The design differences among wood stove models and chimney configurations, and differences in firewood and heat demand all have their effects on wood burning practice. That is to say, we users must adapt to conditions and learn by experience the best way to operate our wood heat systems to achieve the twin goals of high efficiency and low emissions. Given that limitation, however, here are some guidelines that might be useful.
To begin with, the operating instructions supplied with the heater should be followed, especially the procedures for operating catalytic stoves.
In general – all of these suggestions are generalities – wood burns best in cycles. A cycle begins with the placement of several pieces of wood on a coal bed and ends when that wood has burned to a similar-sized coal bed. Adding one or two pieces per hour in the attempt to maintain constant heat output is not a good strategy. In fact, adding only one or two pieces is not a good idea at any time. When loading, always add at least three pieces to create a triangular formation where the glowing surfaces of one burning piece radiate on the other pieces, creating the site where a fire ignites and is sustained. To burn in cycles, wait to reload until you notice that the room or space is beginning to cool off, then add a load of at least three pieces, and preferably more.
Match the size of the load to heat demand. That is, in the relatively mild weather of spring and fall, use several small(ish) pieces of wood, rather than fewer of the large pieces you would use in colder weather. A cycle should last between four and eight hours, depending on a variety of circumstances. For example in spring and fall, I like to use the 'flash fire' technique, which consists of three to six small pieces of firewood placed in a crisscross arrangement and burned fairly fast. The result is about four hours of heating, no smoldering and no overheating of the space. In colder weather, use larger pieces crisscrossed for short fires. For extended overnight burns, load the wood compactly in the firebox to slow down the rate at which it decomposes and burns.
Never let a fire smolder. In advanced, EPA certified stoves, the wood should be flaming brightly when you go to bed at night and you should still have plenty of coals in the morning with which to rekindle the next fire. Gone are the days of "banking" fires with huge unsplit "blocks" and choking off the air supply before bed, a procedure that wasted much of the wood's potential energy and coated the chimney with flammable creosote. The new stoves call for new operating procedures.
Remove ashes frequently. Don't let them build up in the firebox or ash pan. In the firebox they interfere with proper loading and make dealing with the coal bed more difficult. In stoves with ash pans, the forgetful owner who doesn't empty ashes frequently enough ends up with a dusty mess to clean up as ashes end up everywhere under and inside the stove body. In cold weather, I remove a small amount of ash from my firebox every morning before loading.
Much more could be said about the finer points of modern wood stove operation, but with these basic ideas and a good attitude as a starting point, you can develop your own special practices that suit your system, firewood and heat demand. And that's part of the pleasure of heating with wood.
Some environmentalists take a dim view of wood energy, seeing it as crude and backward and just plain polluting. But any serious analysis of a post-fossil fuel future, in which renewables dominate as they must, cannot escape the limitations of solar and wind as producers of the bulk heat needed to warm houses in moderate to cold climates.
Instead of ignoring wood and hoping it will go the way of coal-burning power plants and toxic pesticides, we environmentalists should confront the issue head-on by forcing wood energy into the twenty-first century. We should promote advanced combustion technologies and the social responsibility of using them appropriately. Those of us who choose to heat with wood need to pledge our commitment never to make visible smoke, an outcome that, with care, is achievable now.