On which wood to burn

17 Jan 2007

Got questions about the environment? Ask Umbra.

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

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Dearest Wendy,

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.

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.

Oakily,
Umbra

Yours is to wonder why, hers is to answer (or try). Please send Umbra any nagging question pertaining to the environment -- but first check out her FAQs!

The claims made in this column may not reflect the views of this magazine. Neither the magazine nor the author guarantees that any advice contained in this column is wise or safe. Please use this column at your own risk.

Umbra Fisk is Grist Research Associate II, Hardcover and Periodicals Unit, floors 2B-4B.

Comments: (8 comments)

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Firewood BTUs

To continue the conversation, if you want to know the BTUs per cord (a stack of split wood 4 feet by 4 feet by 8 feet)of seasoned hardwood or softwood, check out this article from Mother Earth News magazine, the largest environmental magazine in the U.S.
http://www.motherearthnews.com/Alternative_Energy/1994_Oc...

by Barefoot at 11:01 AM on 17 Jan 2007

But woodstoves - poor air quality?

First, yes, fruitwoods make wonderful wood for burning. My parents live on a 10-acre walnut orchard, and as trees die over time, they get endless amounts of dense, "clean"-burning wood.

But I have a question for Umbra (or anyone else). I live in the Sacramento area, where they are considering outlawing wood burning because during the winter, we have multiple days of "unhealthy" or "unhealthy for sensitive groups" AQI, in no small part due to the woodstoves (and yes, vehicles and industry play a role, too). Of course there are many problems associated with using oil heat, and electricity.

So what are we to do? We have been seeing record low temps for the Valley (in low 20's at night), which I believe we will continue to see each year. Short of dressing in heavy animal pelts (which, naturally, has other enviro concerns), what option is the "least bad" option for heating our homes?

(I should add that Sacramanto Municipal Utility District [SMUD] offers Greenergy, where you can very cheaply [~6 bucks a month] get the equivalent of your home energy use purchased from renewables. So maybe does that weight things in electricity's favor?).

Tara

by inkedbuddha at 11:08 AM on 17 Jan 2007

Hot fire

In my experience of heating with wood here in Maine, where it's finally getting below zero, the hotter the fire the less smoke you see. When my fire is really ticking, all you can see is hot coming out the chimney. When a fire smoulders and makes charcoal, you see more smoke and you also create creosote which can cause a chimney fire if it's allowed to build up. I would never burn a soft resinous wood like pine in my woodstove. Incompletely dried wood will put out smoke, too, because of the moisture in it, and that will also build up creosote. Using a good, air tight stove is also essential for cleanest burning. Still, I know that even a clean burning wood stove puts some pollutants into the air. And not all wood is harvested sustainably. There seem to be no perfect solutions for those of us living in existing houses not retrofitted for alternatives.

by SMLowry at 4:33 PM on 17 Jan 2007

Which pollute less, carbohydrate or nuclear logs

Umbra wrote: a woodstove user in Maine wonders which logs are best for keeping her warm while spewing minimal pollution.

To resolve those needs, these logs are best:
http://images.google.com/images?q=nuclear+fuel+rods

662,000 hits.

And this type of home may reduce heating needs:
http://www.monolithic.com/plan_design/green

by Nucbuddy at 9:54 PM on 17 Jan 2007

But what to burn it in?

I agree with all points about BTUs per pound of wood, wood type and density, heat of fire, etc. Adding to that, I'm guessing two more causes of thick black smoke in Maine are short (and thus generally inefficient) chimneys and burning softwoods, mostly pine, which is cheap but (to borrow language from American Idol) pitchy.

That said, to talk about what wood to burn without mentioning what stove to burn it in is like having a discussion about gas vs. biofuels without mentioning whether you're driving a Hummer or a Smart Car.

In the fall of 1991, not long after finishing building my own house in the Blue Ridge foothills south of Charlottesville, VA, the day came when it was cold enough to light my brand new Vermont Castings Intrepid stove, complete with catalytic combuster (which reburns the particulates in the smoke). I put some seasoned hickory in the stove, lit a fire, and when it was going good, I ran up the big hill near the house, so I could snap a photo of my snug little home with curls of storybook smoke rising from its chimney. Boy, was I surprised when I looked down and saw barely a hint of flickering heat wafting above the chimney, looking no more picturesque than the vent duct of a suburban gas furnace. Which of course is a good thing, and I quickly got over my disappointment, especially because my super-efficient stove meant splitting less wood. All to say, the stove you use (if you burn wood), like the car you drive (if you drive), makes a HUGE difference.

Sea Wolf

by Sea Wolf at 7:08 AM on 19 Jan 2007

airtight

Okay, I guess maybe with hickory an airtight stove burns most efficiently, but my experience--growing up in New Mexico with only a woodstove for heat and only softwoods to burn--was that when we got an airtight stove, we were never able to get the fires as hot or as clean except by leaving the door open, thus nullifying the "efficiency" vs. our old, drafty stove.

Softwoods only gum up your chimney (and your atmosphere) if you let them smolder.

by willa at 7:43 AM on 19 Jan 2007

Be careful about your firewood.

Ohio, along with many other states around the Great Lakes, is currently under siege from the Emerald Ash Borer. The borer, an exotic, promises to do to our native ash trees, what the Dutch Elm disease and the Chestnut blight did to our native elms and chestnuts.

One of the reasons the bug has spread so quickly is the trade in firewood where diseased ash firewood can be transported for hundred of miles, giving the bug a chance to spread to new areas.

So only burn wood that you know comes from your local area, and burn it completely. Otherwise you may be helping to drive another nail in the coffin of an important American hardwood. For more info: www.emeraldashborer.info

randino

Randy Cunningham

by randino at 1:16 PM on 20 Jan 2007

Fire and sun

I survived school working as a fireman and selling firewood, though I never had the same customer for both.

We heat exclusively with sunlight and firewood, mostly Doug Fir. Burn it hot. We need about two chords per winter. (Western Washington has tons of windblown firewood from our storm.) One chord is worth 3 to 4 barrels of oil.

Our sun system is like an attached greenhouse. We get the equivalent of one barrel of oil per 14 days of sun. If you need to retrofit an existing building with an attached greenhouse then use a Trombe wall between the home and greenhouse and locate your hot water preheat somewhere in the greenhouse. I buried rows of plastic pipe in the greenhouse concrete floor for hot water preheat.

by sunflower at 2:35 PM on 20 Jan 2007

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