Ready for a woodstove? Here is how to decide.
Fireplaces were often found to be energy losers, pulling more heat up the chimney than they put into the house. Many homeowners modified their fireplaces with glass doors and heat-circulating tubes, increasing fuel-consuming efficiency to as much as 50 percent--but more typically to only 20 percent.
People serious about wood heating turned to woodstoves or fireplace inserts. More than 500 American manufacturers, many very small, joined European and Asian importers in responding to the demand. Some of these early stoves were safe, efficient, well-built heaters; many weren't.
Today, about 200 manufacturers produce some 450 models. Stoves are by and large better built, more thoroughly tested, more efficient, and--if installed correctly--safer. They are also a significant investment: count on spending $400 to more than $2,000, with delivery and chimney installation often additional. Do you want a stove? Which one?
A woodstove can be economical. With a plentiful wood supply and proper installation, it can pay for itself in a couple of years, especially if utility rates are high and your current heating is inadequate.
But a woodstove is also a life-style decision. Finding, buying, carrying, splitting, and stacking wood, stocking and tending the fire, dumping ashes--these are details that you have to enjoy, because they become a part of your life. If you buy a stove for only occasional use, you're making a choice based on the pleasure you derive from it, not its energy economy.
If you decide you want to give woodstoves a closer look, how do you choose from among the 450 models? On these six pages, we show the general range of stoves available, how they work, how to install them, and how to burn wood in them.
Although most woodstoves still look somewhat reminiscent of Casey Jones' locomotive, esthetics have been addressed. Technology has advanced the quality of clear glass and ceramic material, so now you can see most of the fire and still have airtight operation. Some stoves feature "self-cleaning" designs that use the intake air to "wash" the glass surfaces; for others, dealers sell special cleaners to keep the glass clear.
You'll also find many new options and choices in shapes, colors, materials, decorative designs, and accessories. The ones pictured on these pages are but a sampling of those available. Stoves specifically designed to be inserted into fireplaces are one of the newest alternatives. "Cats" for better burning
The proliferation of woodstoves has raised new issues. Smoke pollution is a problem in some Western communities (for a dicussion of this topic, see page 314).
Because firewood can be expensive and hard to come by for urban and suburban burners, today's better stoves work harder: they burn smaller wood loads more completely and transfer heat into the room more efficiently.
Many state-of-the-art stoves feature a catalytic combustor--similiar to the smog-control device on your car. It's the ceramic cylinder shown on page 121. Not only do these devices make stoves burn cleaner, but they can raise heating efficiency. By letting woodsmoke burn at a much lower temperature, they release heat energy that would otherwise just go up the flue.
Airtight stoves are notorious producers of creosote and pollutants, especially when operated at the low to medium burn rates typical in most temperate Western climates. The catalytic combustor burns off 75 to 90 percent of the creosote-forming gases and pollutants. Depending on the installation, the addition of a "cat" can mean as much as a 20 percent gain in a stove's heating efficiency.
All surfaces of the combustor are coated with catalytic metals--platinum, palladium, rhodium, or a combination. Once the unit is warmed to about 500[deg.], fuel molecules that pass through it and encounter the metal are chemically changed so they burn at about 500[deg.] to 600 [deg.] instead of their normal 1100[deg.]. The combustor will continue to work, generating its own heat, practically until the fire dies. Cats cost $150 to $200 and are available built into new stoves or as retrofit kits. Used correctly, they have about a five-year life, at which point the cylinder is replaced. In a catalyst-equipped stove, you can burn only wood and the little bit of paper it takes to start a fire (just as you can burn only unleaded gas in a catalyst-equipped car). Garbage, chemically treated papers, or painted wood can poison the unit, rendering it useless. Anatomy of a stove
Most stoves are either cast iron or welded plate steel. The firebox may be lined with refractory brick and the outside skin may be soapstone or ceramic tile, but stripped down, a stove is still just a metal box.
It's that metal box that makes it work. Whereas most of the heat in a fireplace goes up the chimney, most of the heat in a woodstove radiates through its metal enclosure out into the room. Maximum heat transter--achieved by the right combination of design and materials--is one mark of the best stoves on the market.
Stoves channel heat and smoke frm the firebox along surfaces that can absorb and reradiate the heat, as you see in the drawing at left. During this process, just enough air should enter the firebox with sufficient turbulence to maintain proper combustion and chimney draw, but not so much air that the fire burns too fast, is cooled, or draws heat wastefully up the chimney.
But some heat must go up the chimney to ensure proper draft; this keeps the stove from smoking and prevents creosote buildup in the flue. Creosote is a messy, smelly smoke condensate; if ignited, it can cause a serious chimney fire.
Ideally, the heat within the stove is sufficient to maintain a continuous, hot, yet slow-burning fire, while igniting the gases that would go up the chimney in a nonairtight stove or fireplace. Radiators versus circulators
Most stoves are radiators: they have a single thick layer of metal (or another material like masonry or stone) that gets very hot, about 500 [deg.] to 900 [deg.]. This energy is released into the room as radiant heat.
Cast iron and plate steel both conduct heat beautifully. A well-made steel stove can equal the performance of a well-made cast stove, though its lifetime may be somewhat shorter, since plate steel is more prone to heat fatigure, resulting in cracks and scaling. To minimize fatigue to the metal, fireboxes in some stoves are lined with additional metal or firebrick.
Other stoves, called circulators or convectives, have one or two metal layers surrounding the first. Air is circulated--with the help of an electric fan--between the layers, carrying the energy out into the room in the form of heated air, or convective heat.
Many fireplace inserts combine elements of both designs, providing large radiant surfaces that face the room and circulating jackets on the other sides to capture heat that would otherwise be lost.
Radiant stoves are sometimes faster, more efficient heaters, but their outer surface gets hot enough to burn you if you touch it. Some people prefer circulators because their outer surfaces don't get as hot, making them safer for children and a little more comfortable to be near. And generally they don't need as much clearance from combustibles as radiant stoves. Making your choice
As well as answering esthetic and budget questions, you'll have to decide where your stove will go, what heating requirements will be placed on it, what features make sense for your installation.
Work with an established, reputable dealer. Try to find one who has carried the same stoves for a few years and can provide customer references. Better dealers carry a number of stove lines, stock replacement parts and accessories, and provide or refer you to installers who guarantee and insure their work. These dealers will also know local code requirements.
Visit several dealers and play with several stoves to familiarize yourself with the general operation of each unit. See what features appeal to you. Placement and configuration of such items as firebox doors, handles, damper and flue controls, and ash drawers will make a big difference later in safe, convenient operation. What size should you get?
Because woodstoves don't operate at a constant temperature, their heating capabilities are hard to calculate. And BTU ratings for stoves (like those for furnaces and air conditioners) aren't clear indicators. They're determined during safety testing under controlled conditions you're unlikely to duplicate at home.
By the way, a BTU, or British thermal unit, is the amount of energy it takes to increase the temperature of a pound of water by 1[deg.]F. Usually measured over time, it's averaged for stoves, as there are great fluctuations during a burn cycle.
Output ratings are useful for comparing different stoves, but they give only a general idea of performance in your home. Real-world performance, however, is greatly affected by kinds of wood, size of loads, how cold it is, how long the stove has been burning, and other factors.
Many buyers end up with a unit one or two sizes too big, and an oversize stove can literally drive you out of the room. "It's better to use a smaller stove to capacity than underland a bigger stove," warns Mell Rottiers of Golden Flame, Redwood City, California. A good dealer can recommend a stove based on your needs and installation, rather than relying solely on what can be an unrealistic measurement for your conditions. Where the stove goes: more options
Ten years ago, code required that a stove could sit no closer than 36 inches from combustible walls. Now, many stoves have heat shields that let units go 6 inches away from shielded walls, 10 inches from unshielded ones. "It's great for the owner: it's easier to shield a stove than a wall," notes Jay Fenton of Energy Unlimited in Point Richmond, California. Heat shields beneath the stove also can minimize the thickness of noncombustible hearth. These changes have allowed installations that were not possible before, with much less commitment of floor space.
Metal chimmey pipes have also gotten more sophisticated. Stainless steel is becoming the most highly regarded pipe lining, since creosote doesn't build up on it as readily as on conventional flue pipe. Recommendations for safer retrofits
The most notable change is in retrofits to existing chimneys. Ten years ago, you could simply put a metal plate over the opening to your fireplace and run a pipe from the woodstove into the opening.
The recommendation then changed to putting the plate above the fireplace damper and running the pipe to that. The most recent recommendation by the National Fire Protection Association requires that flue pipe run up the chimney to at least the first terra cotta flue tile, usually 2 to 4 feet above the damper.
With face- or damper-sealed installations, the initial simplicity of installation brings trouble later. Stove and plate have to be pulled out for cleaning. Creosote dangers are much greater because the smoke tends to stop moving when it reaches the chimney's larger opening. Some of these installations are "chimney fire time bombs," one stove dealer told us.
Most fireplace flues are greatly oversized for woodstoves. The safest and most energy-efficient installations run new pipe up to the top of the chimney, as you use on page 124, or involve pouring a special cement around a form that's been sized to your the recommendation.
With the flue thoroughly insulated and sized correctly to the stove throughout its run, the stove draws better and creosote buildup is minimized. Cleaning can be done with standard brushes from the roof.
The drawback to these efficient flues is that they dramatically increase the cost of chimney installation. If work is done by the same dealer who sold you your stove, charges typically run about 40 percent of the total bill. Do-it-yourself systems on the market allow you to retrofit pipe to a chimney all the way up to the roof, but they're uninsulated and still prone to excessive creosote buildup. The chimney is the most critical part of a safe and efficient woodstove installation, so it's often best to let a professional do the job. For further reading
For more on woodstoves, three books by Jay W. Shelton, probably the nation's leading authority on wood heating, will be of interest: Solid Fuels Encyclopedia and Wood Heat Safety (Garden Way Publishing, 1983, $12.95; and 1979, $8.95, respectively), and The Woodburners Encyclopedia, with Andrew Shapiro (Vermont Crossroads Press, 1976; $6.95). For design ideas, see Sunset Homeowner's Guide to Wood Stoves (Lane Publishing Co., 1979; $4.95). You might also want to check the buyer's guide Woodheat/85 Woodstove Directory (Energy Publications, Box 2008, Laconia, N.H. 03247; $2.95, $5 by mail).
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|Date:||Nov 1, 1984|
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