As days grow cooler, consider snuggling up to a Siberian stove

When summer fades into fall, thoughts of splitting wood to lower heating costs begin to surface in many homes. Can the wood burning be done without increasing air pollution? One answer may be to turn to the masonry stove, now available in build-it-in-a-day kit form. As Gretchen Poisson tells it, she grew up in the days when oil wells never ran dry and the price of a barrel of crude was such that you could heat a house for just pennies a night even in the far north. Under such circumstances, who needed to dress warmly indoors? As a child her shoes came off the moment she entered the house, no matter how deep the snow or how fiercely the north wind blew.

It was the sort of casual comfort that disappeared for good with the Arab oil embargo of 1973-74 -- or so she thought. Then late in 1983 she and her husband, Lee, installed a masonry, or Russian, stove in their 2,000-square-foot home here and ever since have had all the winter warmth they could ever want.

Moreover, their fuel costs are far below 1950 oil prices because the pine slab they burn is free for the taking in their area. As Mrs. Poisson puts it, winter evenings are once again made for ``cotton pajamas and bare feet.''

The Poissons' experience is similar to that of hundreds of others who have had Russian stoves built in their homes. What makes theirs different is its cost -- under $2,000, or roughly one-third the cost of a conventional Russian stove -- and the fact that Mr. Poisson and two friends erected, rather than built, the stove.

They did so in just one day and fired it the same night -- two other remarkable advantages of this do-it-yourself stove. The Siberian, as it is named, takes up 16 square feet of floor space and stands 6 feet tall. The word ``erected'' is worth noting, as the stove, all five tons of it, is not held together with mortar but rather is laid up, Lincoln Log fashion, one block on top of another.

Weight, along with tongue-and-groove corners, holds the blocks together, while a flexible sealant between each row ensures airtightness. This also allows the stove to expand and contract freely without cracking or breaking the seal, as conventional masonry stoves are inclined to do.

This simple method of erection and the straightforward design of the stove means that masonry skills are not required. A homeowner with one or two friends (the blocks of refractory cement weigh up to 150 pounds apiece) can put the stove together in a single day.

The Poisson home, built largely of poured concrete before energy costs skyrocketed, has conventional insulation and many single-pane windows. Heavy sweaters formed the standard indoor dress code in cold weather. So the Poissons debated whether to blow more insulation into the walls or have a Russian stove installed -- both expensive options. Then they heard of the do-it-yourself Siberian and took that route.

``Now we have heat to spare, burn less wood, and have no creosote problems in the chimney,'' Mr. Poisson says.

Russian stoves, including the Siberian, are among the cleanest-burning furnaces available, superior even to catalytic wood stoves. The intense heat (around 2,000 degrees F.) means that all smoke is burned. Tests show the Siberian efficiency exceeds 90 percent. One indication of this is the absence of carbon in the firebox. Where most stove interiors are black with soot, the Siberian firebox is white, showing that all the carbon has been consumed. The fact that the burn is so clean and the firebox surrou nded by so much masonry makes it perhaps the most fireproof of all furnaces.

Siberian owners have a demonstration they like to give to first-time guests. ``Showing off'' is Mrs. Poisson's term for it. When the fire has reached its peak, an empty aluminum beverage can is thrown into the firebox where it disintegrates in a flash. As Mr. Poisson puts it: ``It doesn't melt, it vaporizes.''

This ability to ``burn clean'' is one reason why virtually any nonexplosive fuel can be used in the Russian stove.

When burned in a conventional wood stove, pine produces a lot of creosote because of the unburned pitch it gives off. In a Russian stove this same pitch burns, becoming part of the fuel, and thus produces still more warmth for the house. This means that pine slabs (the first trimmings taken from a log at lumber mills), which cannot be given away in most forested regions, make an excellent fuel.

Some Russian-stove owners burn throw-away corrugated cardboard, available from stores in the neighborhood. A century ago some immigrants from central Europe built these masonry stoves and fired them with the only fuel readily available in the Great Plains -- grass.

The more rapidly a fire burns, the more energy is extracted from the fuel, and the cleaner the burn. Conventional iron stoves could not withstand such high temperatures and in addition most of the heat would be lost up the chimney. A masonry stove, however, is able to store all this heat in its tremendous mass.

The heat is absorbed in the masonry by sending the exiting hot gases (little more than air and water vapor once the fire is roaring) on a circuitous route before exiting up the chimney.

Once charged with heat, the masonry radiates warmth into the house for days. It keeps the Poisson home above 70 degrees F. all day, and at approximately 68 degrees when it comes time to fire it up the next morning, the owners report.

At the Poisson home here, the furnace is charged each morning. In the spring and fall it might be filled just once, but at the height of winter, ``I'll probably add two more armloads before letting the fire burn out,'' Mr. Poisson says. On such occasions the burn might last as long as three hours. After that you can use the firebox to ``bake the best bread ever,'' according to Mrs. Poisson.

You have to learn how to use a masonry stove through trial and error, the Poissons say. Throw in three armloads of wood, when all you need is two, and you'll end up with the sort of indoor temperatures that set the air conditioners humming on a summer day in Houston.

In the winter of 1984 there were several occasions when the Poissons had to leave their front door open although the outside temperature was about 10 degrees F.

The Siberian ``Erector set'' was originally thought up by a Groton, Mass., schoolteacher, Fred Fitzpatrick, in consultation with Mr. Poisson. By employing modern materials (notably refractory cement), a 1,500-year-old technology was effectively brought into the 20th century.

The full kit for the Siberian is available ($1,700 FOB, Groton, Mass.) from Solar Survival, Cherry Hill Road, Harrisville, N.H. 03450. If you want to ``build your own,'' you can buy the plans for $25, also from Solar Survival. The plans show how to construct the simple wood forms in which you can cast your own refractory cement blocks. In this instance, the locally bought materials will probably run between $1,200 and $1,500.