Stoves that Make a Little Wood Go a Long Way

In 1742 Benjamin Franklin boasted that his newest invention, a wood-burning stove, had the “advantage above every other method of warming rooms.” Methods of home heating have changed since then but even today, after more than a century of central heating, variations of Franklin’s open, cast-iron box provide a simple, inexpensive way of heating a room or a small cabin. Today’s stoves burn coal as well as wood and come in a variety of sizes and shapes. Some nurse their burning logs as a smoker nurses a slow cigar, so that a single log lasts more than 20 hours. The best of them can heat a cabin for the winter with half the wood required by older, less efficient stoves.

The key to high efficiency is an airtight firebox. Here, in the main body of the stove, a metal sheet called a baffle slowly circulates the burning gases that account for more than 50 per cent of a wood fire’s heat. As a result, the stove’s surface temperature rises higher and the firebox radiates more heat.

Fireboxes come in sheet metal, plate steel or cast iron. Sheet metal, the least expensive, cools quickly when the fire dies, and tends to warp and to burn through when overheated. Welded plate steel holds heat longer, but it too tends to warp. Cast iron, the most expensive of the three, lasts longest, retains heat best and generally will not warp; it may, how ever, crack when overheated.

Above the firebox, stove parts are more or less standard. Most stoves come with enough stovepipe to reach an 8-foot ceiling; the insulated chimney pipe that runs through the ceiling must be purchased separately, along with a kit of fittings to support the pipe on the roof. Buy enough chimney pipe to meet minimum height requirements. You will also need flashing, a storm collar and a chimney cap to prevent downdrafts and keep rain out of the chimney.

If possible, locate the stove in the middle of the cabin for the best heating; in any location, it should stand at least 3’ away from combustible wall material. If you place the stove closer than that to a wall, choose a location near the gabled peak to avoid the need for an unwieldy length of chimney pipe, and cover the part of the wall behind the stove with fireproof reflecting material to protect against fire and help circulate heat. Whatever the location, protect the floor under the stove with asbestos millboard, bricks or a box of sand or gravel at least 2” deep, and extend this protective bed 1½’ beyond all sides of the stove.

In operation, a high-performance stove creates one special problem—a coating of flammable creosote that collects on the inside of the chimney. If allowed to build up, the sticky, tarlike coating may start a dangerous chimney fire. You can reduce the hazard by lighting a hot fire every day and keeping it going for 15 to 30 minutes to burn off the creosote in small amounts. If creosote deposits do build up, the chimney can be cleaned with special wire brushes or chemicals that are available from stove dealers.

122 A high-efficiency stove. The installation of this modern wood-burning stove began with a sheet of asbestos to protect the floor. The stove itself consists of two chambers, with three air-intake valves in the door. Inside the firebox, firebrick retains heat for better combustion. A baffle at the top of the lower chamber forces burning gases to circulate fully. The upper chamber, fitted with an interior flue, further retards the escape of the gases into the stovepipe.

Above the stove, the stovepipe fits into a section of insulated chimney pipe that runs through a hole in the ceiling. A finishing collar seals the connection of the two pipes, and a segmented trim collar covers the edges of the ceiling hole.

Installing the Stove

123 1. Marking the ceiling opening. After running sections of stovepipe from the firebox to within 18” of the ceiling, drop plumb lines from the ceiling to the top of the pipe to mark the highest and lowest points where pipe will extend through the ceiling, then mark the ceiling at four additional points around the perimeter of the pipe. Remove all the sections of pipe, cover the firebox with cloth or plastic and drill pilot holes through the ceiling and roof at each mark.

Subtract the stovepipe diameter from that of the chimney pipe, add 2” for clearance and , working on the roof, cut an ellipse in the roof to this dimension beyond the pilot holes,

2. Installing the chimney pipe. Push the roof- support section of chimney pipe down through the hole you have cut until the support brackets lie flat on the roof. Nail the brackets in place and add one section of chimney pipe.

124a 3. Tying the pipes together. Secure the finishing collar partway down the stovepipe with setscrews, then push the top of the stovepipe up into the chimney pipe and insert the bottom into the fire- box. Loosen the setscrews on the collar, slide it up flush with the bottom of the chimney pipe and retighten the screws.

If the stovepipe and chimney pipe do not meet, add extra chimney pipe. If the stovepipe is too long, trim the top with metal shears.

124b 4. Installing the flashing. On the roof, spread a generous layer of roofing cement along the lines where the edges of the flashing will rest, slide the flashing down over the chimney and onto the cement and then nail the flashing to the roof. Cover the nails with a second layer of cement, spreading it over the edges of the flashing.

On a pitched roof, like the one shown here, add enough insulated pipe to extend the chimney 2’ higher than any surface within 10’; on a flat roof, erect a chimney at least 3’ high.

125a 5. Putting on the storm collar. Fasten the storm collar around the top of the flashing and cover the crack between the collar and the chimney pipe with roofing cement. Add a chimney cap to the top section of chimney pipe.

125b 6. Putting on the trim collar. For easy fitting and installation, a trim collar comes in sections that resemble a necklace of aluminum rectangles, loose at the inner edges and fastened at the outer edges by open grommets; two or three sections may be needed to make a complete circle around a chimney pipe. To install the sections, arrange the loose edges around the pipe and flush to the ceiling; fasten the collar to the ceiling with 3 nails in every fifth grommet.