Dear Umbra,

I live in Maine, land of many loggers. My home is heated by an oil furnace, and I try to keep the temps down with thermostat timers to use as little oil as possible. I supplement my heat with a wood stove, as many Mainers do, and in my travels I have noticed a big variation in how much smoke is coming through chimneys and stovepipes. Is there a better type of seasoned wood to burn as far as reducing pollutants?

Wendy H.
Freeport, Maine

Dearest Wendy,

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I just happen to have a Wise Man of the Eastern Forests visiting me, whose house has the same multisource heating system as yours, and who was happy to share his applied firewood knowledge with me. I checked out his information and it seems solid. The short answer is: buy a dense wood, buy it split or split it yourself, and give it six months to a year to dry. Mayhap what you see in one chimney vs. another is smoldering, or wet wood, or variation caused by weather and stove type. What you want is a hot, efficient fire followed by well banked coals.

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Pile it on.

Photo: iStockphoto

Apparently all wood has approximately the same BTU value per pound. (We spoke about the British thermal unit about a year ago. Feel free to make your own conjectures about why the British, of all people, quantified heat. Should they have called it the Please Let Us Stop Being Damp Unit?) The trick here is the corollary: a heavy log will contain more BTUs than a comparably sized light log, because it is denser. What makes one wood denser than another? Well, the dense log might come from a deciduous oak tree, which for a portion of the year is leafless and cannot photosynthesize, and hence grows slowly. There will be less pore space in the tree.

Slower growing, denser woods such as oak, beech, and hickory are known as “hardwoods.” Wise Man of the Eastern Forests tells me this is not a botanical term, but is generally applied to deciduous trees. Evergreen trees are generally called softwoods. Softwoods burn easily but with less heat, and are good for kindling or the tail ends of the heating season, when less heat is needed. The more hardwood you can get in your firewood the better. Fruit woods apparently make lovely, hot firewood but take quite a long time to dry sufficiently.

Wetter wood will smolder as the fire struggles with the embedded moisture. You know I don’t mean wood that was wet from the rain. Fresh wood is wet because trees contain moistness in their very beings: the moistness of the forest, the fresh sap running up and down the tree like a nutrient elevator, the tears trees hold inside when they think of all the sorrows of the earth. All this makes the wood wet. So burn well-dried, split wood with the telltale split ends, hollow clunking sounds when banged together, and dried-out skin tone.

The hotter the wood burns, the warmer the house, obviously, and the more heat for your money if you are buying cords of wood. A few other hot hardwood benefits include less creosote in your chimney and a more efficient burn with less smoldering, resulting in less air pollution (see my recent piece on burn barrels for depressing air-pollution tidbits).

A few last thoughts: check out the nice list of woods and their properties here, don’t burn trash in your stove, and have a warm winter.