How to Use a Wood Stove Safely

About Stovepipes

The most obvious function of the stovepipe is to carry smoke, water vapor, and fine ash from the firebox to the atmosphere. But another function, equally important, is to create the draft — or suction — needed to keep air flowing through the firebox.

Many times I’ve set up our little laundry stove outdoors in the summertime, when it is too hot to have a fire in the cabin. It might seem that a stovepipe would be unnecessary out there in the open air, but without a pipe, the smoke can’t tell the difference between the stoke hole and the stovepipe port, and the fire burns sluggishly. As soon as a couple of sections of stovepipe are attached, however, the smoke moves up the pipe and fresh air moves into the firebox to take its place. The oxygen perks up the fire, the stovepipe heats up and draws still better, and the combustion cycle goes on and on.

A stovepipe acts like a siphon, but in reverse: It moves smoke from a lower to a higher level. Like a siphon, its effectiveness is proportional to the difference in elevation between the two ends. In practical terms, this means that a stovepipe can be made to draw more strongly by simply adding another section.

Most commercial wood stoves take pipe five, six, or seven inches in diameter, but four- and eight-inch pipes are also stock items at many hardware stores. Stovepipe is sold open so that it nests for shipment and storage. It has a special self-locking seam that snaps together at the time the pipe is to be installed, making a solid, safe unit. Some stoves come with tapered pipe that is designed to nest one section within the next. In some units, the whole set fits right inside the firebox when not in use.

Stovepipe comes in two standard finishes — galvanized and black. Galvanized pipe has a shiny, silvery surface when it is new, but if the pipe is heated past a certain point, the zinc coating alloys with the sheet-steel base and the luster is permanently lost. Black stovepipe has a shiny, blue-black color which also dulls with use, an application of stove polish from time to time will restore the sheen and keep it looking nice.

Black stovepipe is less expensive than the galvanized type, but it is also made of a lighter-gauge steel which burns out more quickly. Stovepipes usually burn out first along the seam, and a pipe with reasonably sound walls often has to be discarded just because the seam no longer holds it together properly. I always buy the longer-lasting galvanized pipe. When a section starts to burn out, I replace it immediately rather than risk a house fire. The old pipe may get a few more uses the following summer when we fire up the stove outdoors, but when it becomes unsafe, I junk it without regret.

The standard length of each stovepipe section is 24 inches, but since one end is crimped to fit inside the uncrimped end of the next section, the useful length of each section is 22-1/2 inches. Half-sections are also available.

It may seem logical that the crimped end of the stovepipe ought to be up, so that the smoke has a smooth passage from one pipe section to the next. The problem is that, in cold weather, moisture condenses inside the pipe and then runs back down toward the stove. As soon as the black, watery condensate reaches the first joint, it runs out onto the outer surface of the next section down, creating unsightly streaks which give off an unpleasant odor the next time the stovepipe heats up. After a few weeks the pipes look really bad, and — in hard cases — a crust of highly flammable residue may build up where the pipe joins the stove. Thus, an eyesore becomes a safety hazard.

It may seem equally logical that if the crimped ends of the stovepipe sections face down, the edges inside the pipe will catch the smoke and direct it into the room. But it doesn’t work that way. Since the draft is a suction phenomenon, air tends to leak into the pipe instead. With the crimps down, the condensate funnels right past the junctions, toward the stove, where it eventually evaporates. The outside of the pipe remains spotless.

In warm regions, the stovepipe may never really get cold enough for condensation to occur, but in the North Country it can be a real nuisance. Unfortunately, some stove manufacturers seem to have missed this rather important point. They designed their stovepipe collars so that the pipe has to be connected the messy way, with the crimped ends up. I struggled with this problem for some time before figuring out how to make a simple adapter that eliminates the problem altogether.

Occasionally, it is necessary to use two different stovepipe diameters in a single installation, for example, when a stove with provision for a 7-inch pipe is used with a 6-inch chimney connection. Several types of reducing and increasing adapters are on the market but again, many are made the wrong way (with the crimped end up). Once more, custom-made adapters are the only answer.

Stoves with the stovepipe collar at the rear require an elbow to make the connection with the vertical stovepipe. A standard one-piece 90-degree elbow is formed from a short piece of pipe by multiple crimps around the circumference, and comes in both light-gauge black and heavy-gauge galvanized finishes.

Bends of less than 90 degrees require adjustable elbows. Made up of four swiveling sections, these take any angle from 0 to 90 degrees. Since the seams burn out fairly rapidly and may drip condensate, it is unwise to use this kind of elbow in the full 90 degree position where a solid one-piece model will do.

Most wood-stove setups require a damper in the stovepipe. A damper is merely a slightly undersized, perforated cast-iron disk, mounted on a metal shaft in such a way that it forms a butterfly valve inside the pipe. One end of the shaft extends beyond the pipe into the room, and is bent to form a handle. With the damper in the open position, the flue gases have free access to the upper pipe and the atmosphere. With the damper partially or fully closed, gases can escape only through the perforations and the spaces that remain around the edges of the disk.

If two stoves are connected to a single stovepipe, the connection is made by means of a tee. This is merely a short section of standard stovepipe with a collar emerging from it at right angles.

With the addition of a counterbalanced, swiveling flap in the collar opening, a simple tee becomes a draft corrector or draft minder. This ingenious device is designed to overcome excessive draft by admitting a regulated amount of air into the stovepipe. This “spoils” the effective draft at the firebox because much of the suction provided by the chimney is pulling air through the tee rather than through the stove.

A draft corrector is set by adjusting the counterbalance weight so that the flap hangs open just enough to correct the draft for calm-weather operation. Then, on windy days, when a gust suddenly increases the suction on the pipe, the flap merely pivots to a more open position, admitting extra air from the room into the stovepipe. The suction on the firebox remains relatively steady, and the fire burns evenly. When the gust subsides, the flap swings right back to the preselected position. The little flap, creaking back and forth all day in response to every gust, keeps you informed on the progress of the storm outside.

Every wood-stove owner eventually wonders how much of the heat in the flue gases could be captured and used to heat the house. Various types of heat exchangers or “stack robbers” have been developed to meet this need. One popular type consists of a series of horizontal tubes in a boxlike container which is mounted between two joints of stovepipe. Smoke passing around the tubes heats them, and a small fan blows the hot air out into the room. The energy retrieved from the waste heat far exceeds the energy required to operate the fan, and so the unit pays for itself over a period of time. As an added bonus, the fan helps to break up the hot-air layering that generally occurs in rooms heated by wood stoves.

Another simpler type of stack robber consists of a series of shaped metal rings that slip over the first section of stovepipe and act as radiating fins.

This covers the basic stovepipe hardware between the stove and the wall or ceiling. Many kinds of fittings are manufactured for passing stovepipes safely out of a building, and you should discuss them with your local hardware and building supply dealers.

About Firewood

It was my privilege, during my first winter in the Far North, to have access to an entire forest that hadn’t been touched for decades. Dry spruce stood everywhere, consequently, that’s all I burned. It was only later, after moving to a less favored region, that I was forced by necessity to experiment with other species of trees and with wood in other conditions (such as green, half-dry, punky, pitchy, and driftwood). I soon learned that all woods are not created equal, by any means. The same principles apply to the wood types available in other areas, even if the species of trees are different.

Forests in the north are very monotonous compared to those of warmer regions. Our list of firewood species, as a result, is very short: white spruce, black spruce, paper birch, cottonwood, quaking aspen, willow, and alder. But since each of these woods may be found in a variety of types, we actually do have a fair range of distinct kinds of fuel.

The great mainstay of wood-burning stoves throughout most of Alaska is white spruce. (Black spruce is so nearly identical in its firewood properties that, if there is any difference, I have missed it.) Dry spruce, in the local Eskimo dialect is called qirrupiaq — (“real wood”). It is easy to light, responds immediately to the draft, gives a hot fire, and leaves a good bed of coals. It is a forgiving wood: Even if the fire has been neglected until only a few coals remain, a handful of kindling and a few splits of dry spruce will quickly revive it.

Half-dry spruce comes from trees that are almost, but not quite, dead. When a spruce tree is dying, the layer of sapwood under the bark gets thinner and thinner, the heartwood drier and drier. Once the growing tip of the tree dies, the branches follow, one by one. When only a few branches bear green needles, the tree is prime for cutting.

Half-dry spruce combines the advantageous properties of both green and dry wood. If it is laid on a good bed of coals and the draft is opened, it takes right off. If the draft is closed, the wood lies there for a long time, absorbing heat and drying out while the stove marks time. Thus, half-dry spruce can be used either for instant heat or as a holding wood.

Punky spruce is wood that has begun to decay before the tree dies. Rot begins in the center of the trunk near the bottom, then works its way upward and outward toward the bark. The punky wood is orange-colored with myriad little white spots, like some strange cheese. The fibrous texture is gone, so the wood is very easy to saw but difficult to split evenly.

Occasionally, the core of a spruce is punky, while the outer portion of the trunk is firm and heavily encrusted with pitch (especially around the knots). This pitchy wood is handy for rekindling a small fire, since the pitch melts and runs down onto the coals, where it ignites very easily. Pitchy knots are also handy when baking in a wood range, since they produce a quick, hot flame.

Green spruce has a thick layer of resinous sapwood just beneath the bark, and healthy moist wood from there through the core. It may be burned the same day the tree is cut down, but the considerable energy cost of evaporating the excess moisture will have to be paid by wood already on the fire. It is more efficient to cut and split the wood well ahead of time and let it air-dry for a year — even two — before burning it. Personally, I don’t feel right about cutting healthy trees for fuel, and most of the green wood that goes into my stove comes as scrap from building projects. It is handy for holding an overnight fire or for cooling a fire quickly.

Driftwood is always welcome, since the river does the work of hauling it to camp. One spring we made camp along a high riverbank rimmed with a thick deposit of driftwood, and for a month we never had to go more than 20 steps for fuel. Driftwood comes in all types, sizes, and conditions, so — with a little care in selection — it’s possible to find fuel that is suitable for almost any use. Small, dry sticks are fine for cooking, and larger, moister ones are handy for holding a fire. On the minus side, ocean-borne driftwood can carry corrosive salt into the

Oliver Cameron ricks up his willows and alders to dry tipi-fashion stove, and driftwood from any source is likely to be contaminated with more or less saw-dulling sand and silt. Still, in some circumstances it can be a very satisfactory fuel.

Paper birch is the nearest thing we have to the excellent hardwood fuels of the Eastern States. (The rest of our species rank fairly low on any list of preferred woods.) It burns hot, lasts a long time, and produces fine coals. To my mind, the smoke from burning birch is one of the most pleasant smells in the north woods. But in spite of all these fine qualities, I burn very little birch. The living trees are just too beautiful to cut down, and it is hard to find dead ones in burning condition because the bark forms a durable, watertight cylinder that encourages extremely rapid rotting. The odd chunk that comes my way usually goes into the stove at bedtime, when I set the overnight fire.

Cottonwood and aspen rank low on our list of preferred woods. When green they are exceptionally heavy and waterlogged, and when punky they burn without much heat. When properly seasoned they burn well enough, although ash production is high and coal production rather low compared to some other species.

Willows figure prominently in our firewood diet only in spring and summer, when we camp near riverbank thickets. We collect “breakwood”, which is anything that can be harvested without an axe or saw. Dead willows that are still standing are usually fairly dry, and they make a reasonably good fuel. One man here uses very little else; he makes one trip a day all winter to the thicket across the river, and drags the wood back with one dog and a little sled built around an old pair of skis.

Alders in this area rarely get any thicker than a man’s arm, so — as with willows — it takes quite a bit of work to collect any quantity of them. Dry alder can be used much like spruce, although it is a bit slower to start. It produces firm, hot coals, very much like those of birch. Green and half dry alder is handy for holding fires overnight . . . it gives a really intense fire when the draft is opened the following morning. Unfortunately, creosote production is high, and this alone is enough to rule out its use in some installations.

This discussion of our short firewood list shows that — with very few fuel species — we still have enough variety to do whatever needs to be done with our stoves. The same is bound to be true in other areas of the country, even if the species of wood are entirely different. It pays to talk to old-timers about their preferences in woods, and to experiment to see which woods give the best results with any particular stove.