Tom Powers, retired Air Force technical sergeant and member of Peruvian City Council, is monitoring a wide range of issues affecting this city in northeastern New York: zoning issues, local water supply, Road maintenance. In the past two years, one of the main items in his diary was the smoke plumes from a dozen wooden boilers in the backyard of the city.

A number of these wooden boilers are located in the hamlet of Peru, about 750 houses along the banks of the Little Ausable River. The others are scattered around the city, a sample of 80 square miles of rolling woods, farms and apple orchards about 10 miles south of Plattsburg. On a cold and matte gray day earlier this winter, all seemed to be in the process of operating, the lazy spiral in the descending clouds.

These exterior boilers burn wood – and almost anything else – and usually provide heat to one or more buildings at much less cost than it takes to heat a house or barn or greenhouse with Oil or propane, a growing disparity The cost of oil is increasing.
Smoke, however, is a very serious problem. Most exterior wood boilers are paramount from an engineering point of view – simply metal boxes surrounded by a small water jacket. The wood burns in the box and heats the water, which is distributed to the building. If it is inconvenient for the owner to cook the boiler, he can charge it with fuel every 12 to 24 hours or so and adjust the thermostat so that it produces a constant heat wire all day.

Burned in this way, the fire only crosses paper during much of its burning cycle, sending smoke out of the pile. The piers are usually fairly short, roughly half the height of the roof line of a two-storey house, which means that the smoke can form a hug near the ground. If there are neighboring neighbors, their homes may be invaded by smoke. The problem is exacerbated when operators burn green or wet wood or, worse, things like garbage cans or old tires that some do.

At the same time, potentially external boilers are a very cost-effective way to use firewood, which has enormous supply, particularly in the heavily forested areas of the northern US. In addition, burning wood for fuel is sustainable because wood, unlike coal or oil, is a renewable resource. Replacing these fuels with wood reduces the user’s carbon footprint and thus reduces global warming. And these boilers can be burned cleanly. Some producers have developed boilers with considerably reduced emissions and increased efficiencies. It is more expensive to install, but the savings from more efficient use of fuel help to reduce the initial investment.

These factors – the threat of low wood smoke, the prospect of significant financial savings and potential environmental benefits – have combined to constitute a highly controversial public issue. Some states, including Vermont and Maine, and later Michigan and Washington, have established strict constraints on boiler emissions. New York is currently developing a state-wide regulation. Meanwhile, many municipal governments, particularly New York and Massachusetts, have moved alone to regulate outdoor boilers.

In response, the boiler industry has mounted an aggressive campaign to protect its right to continue producing boilers of all types, including poorly designed and wetter units.

Heating with wood

For a process whose roots have fallen back into prehistory, burning wood to generate heat can be surprisingly complex. In this country we started with chimneys, where much of the heat went directly into the chimney, and then we moved to various types of stoves inside. The generation of wood stoves that appeared in the mid-1960s was not much more efficient than chimneys. The fact that they can be mitigated – deprived of a filling of air – meant that an owner could load them, stifle the flow of air, and then obtain a more or less stable heat flow for hours.

The choking of the air supply, however, is an inefficient way to get out of the heat from the fuel and also very dirty: these stoves generated a lot of smoke and pollution, and that was a major problem. In a city like Waterbury, Vermont, which is in a bowl of hills along the Winooski River, a winter inversion of temperature could trap the smoke near the ground and make the city almost uninhabitable.

In response to the public breathlessness on this issue, Environment (EPA) issued rules in 1988 obliged manufacturers of wood stoves to improve their products. Older cookers, pre-EPA certification, generally emit 40 to 60 grams of fine particles in the air every hour. Once manufacturers were required to meet EPA standards, the allowable limit was first set at 8.5 grams per hour; In 1990, this limit was cut to 7.5 grams per hour (4.1 grams for catalytic stoves). So to stay in business, manufacturers have completely redesigned wood stoves with catalytic converters or improved airflow to burn wood efficiently and cleanly.

These regulations, however, have exempted wood-fired central heating appliances, including outdoor wood boilers. When manufacturers have recently begun to accelerate the production of these devices, many of them have used the same inefficient box technology as forbidden interior stoves, which is simpler and cheaper to manufacture – and as smoked as Prohibited wood pits.

Even the cleanest wood stove emits pollutants, which can include soot, fly ash, creosote and heavy metals. These chemicals can be very dangerous in themselves, but perhaps the greatest danger of wood smoke is that the particles produced can be very small, smaller than 2.5 microns. One micron is one millionth of a meter and 2.5 microns is about one-20th of the diameter of human hair. When a person breathes these tiny particles, they penetrate deep into the lungs, bypassing the normal respiratory tract structures that catch larger particles. All particles less than one micron in size do not penetrate only the deepest part of the lungs but also directly into the bloodstream. A growing body of medical research shows that these particles are carcinogenic and dangerous to human health.

Proven technology

It does not necessarily have to be that way. There are outdoor boilers on the market that can burn wood with negligible emissions and a minor health hazard, producing even cleaner smoke than the new EPA certified wood stoves. One is the Garn Boiler, produced by the Dectra Corporation of St. Anthony, Minnesota. The Garn, which stands out in the air, resembles a miniature tank car, constructed of solid steel and well insulated. The main combustion chamber is a fairly small box that is inside a large pool of water that acts as a heat sink.

The air is sucked into the unit by a constant rotating fan and is divided into two streams before it enters an insulated combustion chamber. The lower stream passes through the burning logs and generates a very hot fire. The second flow passes over the combustion chamber and collects the volatile gases released by the combustion logs. This stream enters a secondary combustion chamber, where these gases are themselves burnt. The remaining exhaust, most of the water vapor, passes through a serpentine exhaust system that flows through the water basin, enveloping even more heat.

This kind of wood gasification boiler solves the problem of emissions by addressing the fundamental physics of the issue, namely that wood burning and heat storage must be treated in two distinct stages. In order for the wood to be burned efficiently, it requires a well insulated chimney with plenty of air circulation for high temperature combustion. For the resulting heat to be used effectively, it requires a large storage tank that can hold heat between the tie rods. Rather than burning, therefore, a Garn is burned warmer (and less frequently) than low-tech smoke boilers, whose design places a small tank of cold water directly against the chimney.