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Concentration of CO2 in the Atmosphere

Heat with Wood — Past and Present

Great Kitchen, Rochlitz Castle. Photo: Norbert Kaiser, bit.ly/Wikimedia-Rochlitz-kitchen

George Harvey and N.R. Mallery

We hope no one minds if we ramble down memory lane. The history of heating can be instructive.

One of the holiday season’s many customs is to sing about a Yule log. The songs refer to a way of life many may not be aware of, before chimneys existed. In those days, a fire in a home was on a raised hearth or in a fire pit, in the middle of the main room. It was used for heat, as well as cooking.

That was the reason why the great hall of an old castle had such a high ceiling. The smoke was vented in a hole above the fire in the roof or as high as possible on a wall. The great hall was where everyone slept during the winter, because it was the only place that had any heat. Of course, with the wind blowing through the open vents, it was often not very warm.

The great hall also had a problem some people still have today, though this is a medieval problem that has been dealt with. The indoor air was polluted because of all the smoke.

Chimneys seem to have been invented a bit less than a thousand years ago. It seems odd to think that the ancient Romans, consummate engineers, did not develop them, but such is apparently the case. With the invention of the chimney, people could have fireplaces. By the time of King Henry VIII, wealthy people often had fireplaces in their bedrooms. The vented fires were a little safer with somewhat improved indoor air. Sadly, they were also less efficient and more used, leading to both outdoor pollution and loss of forests.

Wood stoves were the next improvement. They were far more efficient for delivering heat to the home, and air quality in homes improved even more. The old wood-burning systems were still not perfect, however. The old cannon or box stove could release smoke, and that smoke is a form of pollution. Their replacement, the now-outdated so-called air-tight stoves, are arguably worse polluters, partly because they starve the fire for oxygen, and that produces carbon monoxide, a pollutant you cannot smell. Also, air-tight stoves can produce a lot of creosote, which can clog a chimney and fuel a chimney fire, not to mention asthma and other health issues. Fortunately, we have new, modern wood stove technology that does not have these problems.

It was common during the 19th century for farmhouses in New England to operate sustainably, using forest products from their own wood lots. But with a growing population, and the increased availability of fossil fuels, many chose to use first coal, and then oil and gas for heating, which appeared to make lives easier. You might say there actually were some benefits from the switch to fossil fuels. They have the advantage over old wood-burning technology, which is that they can produce fewer particulates, both in the home and in the environment. The biggest problems are that fossil fuels are unsustainable and are destroying our climate.

A Discovery series Wood Stove from Quadra-Fire Stoves. Image from quadrature.com

Fortunately, now we have better alternatives. The modern wood stoves built today are engineered to reduce emissions considerably. A wood-burning system that is well designed and maintained can actually be much cleaner than many heating systems using fossil fuels. Clearly cleaner than coal or oil, in terms of pollutants, modern wood stoves do not add to atmospheric carbon the way all fossil fuels do, including gas. A well-managed woodlot is a carbon sink and can actually be part of the solution. The low amounts of carbon dioxide that are still released come indirectly from the atmosphere, so the net addition to the atmosphere can be very low. (Note: can be.)

Today’s wood stoves produce low emissions and release low particulates via different technologies. One is to have a catalytic converter in the stove. This causes more complete combustion of the fuel, making the exhaust gases much cleaner, with far lower particulates.

However since the catalyst needs to be replaced after a period of time, at rather high cost, some modern stoves have a non-catalytic design that does not need it. Modern stoves with non-catalytic designs produce relatively particulate-free exhaust by having a secondary burn after a hot initial burn via chambers built into the design with lower emissions. The higher initial burn temperatures must be maintained to keep the system relatively clean, but the stove does this automatically in normal practice.

Pellet stoves operate at very high temperatures so their fuel burns completely and cleanly in a pyrolyzing chamber or firebox. Most of these stoves have fuel fed by an augur, and their air flow is regulated automatically, so they can operate with minimal human supervision.

Froling S3 Turbo wood boiler, courtesy of Tarm Biomass.

Another option is central heating fueled by wood or wood pellets. Modern wood and wood pellet boilers and furnaces often use precise combustion controls that measure the temperature and residual oxygen content of exhaust to fine tune air or fuel mixes. Special combustion chambers with advanced computer modeling are designed to provide precise air and fuel mixes and high temperatures for clean combustion. Boilers and furnaces are not made with decoration and fire viewing as major design considerations, and they achieve excellent efficiency and produce very few emissions. Chipped wood and wood pellets enable automation that makes modern boilers excellent renewable heating sources for everything from passive houses to large industrial or municipal buildings.

With forestry practices that provide wood fuel sustainably, modern wood stoves can be about as environmentally sound as combustion heating can get, using the newest technology. (See “Advanced Wood Heating,” in the December, 2017 edition of G.E.T. (bit.ly/GET-advanced-wood). There are a lot of old (pre-EPA regulation stoves sold prior to 1990) wood-burning stoves in use in the Northeast, and environmentally conscious people might want to upgrade them. Fortunately, states sometimes run incentive and change-out programs to make this affordable.

New Hampshire has a Residential Bulk-Fed Wood-Pellet Central Boilers and Furnace Rebate Program (http://bit.ly/wood-in-nh).

New York has a Residential Pellet Stove Program (http://bit.ly/pellet-ny).

Massachusetts has a wood stove change-out program that runs through 2019 (http://bit.ly/mass-changeout).

Various incentives in Vermont, including for heating with wood, are found online (http://bit.ly/vt-incentives).

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