Burning wood is cheap, but coal has its advantages

Alternative space-heating fuels are by nature more bothersome than electricity, gas, or oil. However, judicious use of wood or coal may save a considerable amount of money and provide a warmer, cozier home.

Here is a look at the relative merits of these two most widely used home-heating alternatives:

* Storage space. The normal unit measurement of wood is a cord - 128 cubic feet, or a space 4 by 4 by 8 feet.

A typical household may burn 3 to 6 cords a year, which results in a lot of usurped space.

Coal is usually sold by the ton, which occupies less than 40 cubic feet - or a space of about 3 by 3 by 4 feet.

In British thermal units (B.t.u.) of heat potential, about 11/3 cords of good red maple equals a ton of coal.

* Seasoning. Wood should be seasoned, or air-dried, to about 20 percent moisture content before it is burned. This takes about 6 months or even longer.

Coal needs no seasoning because its moisture content is virtually nil. Nevertheless, coal should be bought from a reliable dealer who supplies anthracite free of excess material and dust.

* Availability. Good hardwood is more plentiful on the East Coast than elsewhere in the United States. Your own woodlot of 8 to 10 acres may be renewable and self-sustaining, but you'll be busy preparing the cordwood.

Buying wood from wood dealers is easier, but dealers are sometimes reluctant to deliver wood in midwinter.

Coal miners share this reluctance, and strikes may shut off the supply. Thus, it is wise to get your coal supply early as well.

* Cost. Delivered wood is cheaper in 4-foot lengths, because less labor is involved. This means, however, that you must spend your own time cutting it to size to fit your stove. Nevertheless, wood is generally cheaper in rural areas. In cities the price of wood may be the equivalent of oil in B.t.u. heat potential.

In terms of B.t.u. equivalency, coal costs are generally somewhere between wood and oil. This also depends on your location.

* Chimney fires. Burning wood in an airtight stove requires a slow fire. This , in turn, emits high doses of pyroligneous acid, or creosote. The creosote sticks to flues. If there is too much of it in the flue, it could ignite and cause a chimney fire.

Cleaning chimneys and stoves is important, and it adds to the cost of burning wood.

Coal, in contrast, generates no creosote.

* Pollution. Wood emits a negligible amount of sulfur (0.02 percent). However , other particulates from wood fires have caused alarm because of the pall that can often be seen over such communities as Portland, Ore.; Waterbury, Vt.; and Aspen, Colo.

Anthracite emits 0.52 percent sulfur and traces of carbon monoxide.

As with wood stoves, coal must always be burned with a slightly open window in order to resupply oxygen that coal or wood fires consume. Secondary air intakes of modern stoves burn off carbon monoxide.

* Burning rates. Depending on the size and quality of design, wood stoves may need fuel resupply and attention twice a day - and often double that.

Coal ignites at a temperature more than 100 degrees higher than wood, and it requires a hot bed of wood coals to get it started. Being far denser than wood, coal burns more steadily and longer. Coal stoves may need attention only twice a day at most, and they may burn more than two days before they need to be resupplied, depending on the stove.

* Ashes. Wood produces about 60 pounds of ash per cord, and the residue may be used for vegetable gardens.

Anthracite coal generates 8 to 10 percent ash per ton - more than wood. The ashes are not good for vegetables, but they may be used to fill potholes and to provide traction on slippery walkways.