SHADES OF GREEN: Wood heat

I shouldn’t do this. It’s spring, finally, and enough about the cold, already. Still, this is Wisconsin, after all, and we have to face facts. Winter will come again. Eventually. Sooner than some of us would like.

So how can we green up our approach to heating?

To begin with, we can look at the state of our conventional heating equipment. What comes first in sustainability is conservation and efficiency, remember. Furnaces and boilers – whether fueled by natural gas, oil, or propane – have come a long way in the last several decades, and an upgrade may be warranted.

Even the combustion efficiency of oil burners has improved a lot in recent years. Furnaces have for some time been called “condensing furnaces,” because their efficiency is so high that the vented stack gasses are not warm enough to carry off the water vapor formed by combustion, and some provision must be made to drain off the condensed moisture.

Aside from the fossil fuel burning world we are familiar with, what else is out there?

One is burning wood. You might ask, since this is still combustion, whether all the carbon dioxide in wood smoke is just going to contribute to global warming, too. Well, no. The short answer is, “it doesn’t count.”

You see, the carbon we are talking about here was taken out of the atmosphere by tree growth recently. The wood you burn now is being replaced by new tree growth all the time.

This is in contrast to the “fossil” (really ancient) carbon we liberate into the atmosphere when we burn oil or coal or gas. Burning that stuff is dumping extra carbon dioxide into the biosphere, stuff that it has taken the planet millions of years to safely squirrel away. Therefore, when we heat either directly with solar or indirectly with the solar-driven production of that stuff called wood, we are displacing the burning of fossil fuel and the “extra” carbon dioxide thus produced.

In the city, burning wood for heat in a serious way is probably not a good idea, because wood smoke is an air pollutant; and if widely done in a neighborhood, all that smoke is not a good thing. In the country, though, it’s another matter, within reason.

The chief barrier to this, aside from wood availability, is the commitment: You think marriage is a commitment? Burning wood seriously for heat is a lot of consistent work. You have to fire up the stove all the time, clean out the ashes, and occasionally sweep the chimney. It can be done. At our solar house the back-up heat is chiefly wood and we burn about three cords a year, which I produce myself. (A cord is a stack of wood 4 by 4 by 8 feet: 128 cubic feet.) All this keeps me fit, but it’s a significant part of my life, year ‘round.

Another way to burn wood that is partly less fussy is to have one of those outside boilers. They come in various sizes and have impressive heating ability. We hear a lot of objection to these units, especially because of the smoke. They burn “at idle” all the time, and the forced-air combustion goes on when heat is called for.

A local dealer for these machines says the smoke problem is overstated. Properly run, the smoke problem is said to be minimal. He says that, contrary to what you would expect, green wood makes less smoke than dry wood. Also, you shouldn’t burn garbage, animal carcasses and such in these things, as some people evidently do. The wood can be quite large pieces, which means a great saving in cutting and splitting, and you only have to load the unit infrequently. (I must confess that I am still skeptical of these devices.)

There are also units that burn grain, which is fed into the device by an auger from a grain hopper. This sounds attractive, even in the sense that it “supports farmers,” but I suspect that unless the grain we are talking about is waste, stuff that is no longer food-grade, the energy investment in growing that grain is going to offset the energy we would get out of it: In other words, aren’t we then just burning oil by proxy?

Pellet stoves are another matter. They have come into their own. They used to be rather fussy, but are now electric start and fairly sophisticated (and complex) devices. The pellets are made, usually, of compressed ground-up wood, or sawdust. These stoves put out impressive heat, and use an available, renewable resource. Different models, from utilitarian to living-room attractive, are available. The combustion vents just go through the wall, and the burning is remarkably clean. Some models are efficient too, at 86 percent or so, and so qualify for certain incentives.

You can expect to pay a bit over $3,000 for a good residential pellet stove. It’s easy to educate yourself about some of the details on the Internet: how such stoves work, the pros and cons of different models, the cost of fuel.

In general, the idea of using woody sources converted into a uniform, transportable fuel – pellets – has great appeal. Austria was a pioneer in pellet burning and was the first country to establish standards for the pellets. Now, across the European Union, household and large-scale installations for heating with pellets are a growth industry. The EU countries produced 9 million tons of pellets last year.

Applications in the U.S. already include not only residential-size situations, but large installations in which the pellets are delivered in bulk to big hoppers outside of a school, say, or a commercial building. The systems are automatic, with the pellets delivered to the boiler by an auger, or being blown in.

All of this is a promising prospect for us here. We have a fair amount of biomass in Wisconsin, and space heating is a big part of our energy needs. Perhaps my previous column, a piece of fiction visualizing the future energy situation here, should have included widespread pellet burning as part of the scenario, now that I think of it.