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

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.

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.

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.

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.