This article is the first Examiner column written by Richard Thornton, exactly three years ago today. At the time, he had just moved out of a tent in the Nantahala Mountains of North Carolina, to temporarily live in an unoccupied cabin in the Smoky Mountains. The only source of heat in the bitterly cold weather was an inefficiently designed fireplace. This discomfort inspired the article. Later it was learned that the cabin had been a hideout for Olympic Games bomber, Eric Rudolph. His experiences while living in the Southern Highlands wilderness would ultimately change the history books.
Somewhere, long ago, a lightening bolt struck a dead tree and set it on fire. One especially clever individual put another dry branch on top of one that was aflame. When that one kindled, he or she placed another and another. Mankind had learned how to control and maintain fire. That is the essence of heating with wood burning fires.
Brief history of heating with wood fires
For most of mankind’s existence, home heating has consisted of an open hearth – essentially a campfire on the floor of the house. Heat emanating from the fire directly raised the temperature of the air of house’s interior, while smoke drifting through a thatched roof. The efficiency of an open hearth is almost 100% since the interior is heated directly. However, excessive smoke could make things quite unpleasant for the occupants, while a spark rising from a large fire could ignite the roof. The effectiveness of an open hearth was dependent on the capability of the house to retain heat, since the hearth itself quickly cooled after the coals died. The choko, a prefabricated, heavily insulated, winter house built by the Creek and Choctaw Indians, could maintain very comfortable interior temperatures during the coldest of winter weather, with only a couple of logs in the hearth.
About 3200 years ago, clay & stone baking ovens were developed by the Greeks, which retained heat in their walls and then radiated it out into the house over a period of time. However, the smoke from the ovens still drifted through the roofs of houses.
The Romans constructed large commercial bakeries that used holes in the walls to conduct smoke out of the buildings, but most homes used charcoal braziers for both heating and cooking. Some large villas did have hollow masonry floors which were heated with wood fires from beneath.
Fireplaces and chimneys were first developed in the 12th century in northern Europe. They solved the problem of smoke and sparks, but about 95% of the heat went up the chimney! That is still the problem with conventional fireplaces today.
The first “wood stoves” for heating were developed in the 1700s in Northern and Eastern Europe. They were a response to dwindling wood sources and consisted of large ceramic structures with chimneys. About the same time, ironworkers in northern England developed a cast iron front for fireplaces that retained more heat, and controlled the flow of air. Benjamin Franklin developed the concept further by designing a free standing cast iron stove, which radiated heat in all directions.
The technology for wood heating changed little until the late 1980s, when the EPA set minimum standards for the design and efficiency of wood burning stoves. During the late 1970s energy shortages, the “back to nature” movement and policies of the Carter Administration had encouraged many Americans to install wood burning stoves, or even central furnaces, in their homes. These stoves DID substantially reduce energy bills for Americans, who had inexpensive sources of firewood. However, they had several drawbacks. Only about 50-60% of the heat actually radiated into the house. Damp wood and insufficient supply of oxygen caused these stoves to produce large volumes of creosote, smoke and potentially toxic gases. The creosote (congealed smoke) accumulated inside chimney flues until either cleaned out or burning explosively. Another problem with wood stoves was that the interior air temperature dropped as one becomes more distant and isolated from the stove. Pipes could freeze in remote sections of the house, while the room containing the stove was quite comfortable.
Perhaps the most dangerous trait of conventional wood stoves and fireplaces are their potential for creating poisonous gases. The burning wood draws large volumes of air from the house’s interior. This was not usually a problem in historic houses, with their inherent cracks and leaking door frames. However, modern building codes have substantially sealed these gaps where fresh air may enter the interior. When a fire has consumed much of the oxygen in a house, its chemical reactions produce carbon monoxide rather than carbon dioxide. The combination of oxygen deprivation and carbon monoxide can quickly kill the house’s occupants while they sleep.
21st century wood heating technology
Wood stoves produced since the EPA regulations went into effect, use catalytic converters to burn the organic residue in smoke. The new generation wood stoves are designed to efficiently inject combustion air into the fire, while retaining heat in the air tight body of the stove. A homeowner can expect about 70-80% of the heat produced by a modern stove to be radiated into the home. With these new generation stoves, firewood would have to cost over $250 a cord for electrical or gas heating to be more cost efficient. However, there are several other technological innovations that homeowners can install to further reduce their energy bills.
During the late 1970s the presence of Mother Earth News Magazine encouraged a large number of farmsteaders and alternative energy factories to locate in the Asheville, NC area. Wood heating was particular attractive to farmsteaders because petroleum base fuels were trucked into the North Carolina Mountains and therefore, relatively were more expensive than other areas. Also, there was an abundance of firewood in the surrounding Pisgah National Forest. During this period, architects, builders and wood stove manufacturers developed several innovate technologies, which were applied locally, but are usually not seen in other parts of the United States. Most of these innovations were originally shop built by local metal craftsmen or constructed on the building site by contractors.
Firebox with a combustion air intake: The most important innovation from the Asheville area was the firebox. It has seen some acceptance elsewhere, and can even be purchased off the internet. The firebox is a freestanding heavy, wrought steel burning chamber. It has fire resistant glass doors on 1-3 sides. Structural steel welding techniques are utilized to insure air-tightness for the life of the house. The precise construction of the firebox makes possible the connection of the box with outside air via a four inch galvanized metal pipe. Oxygen within the house is only consumed when the firebox doors are open. Combustion air intakes for wood stoves are quite common in the Asheville Area, but are not prevalent elsewhere.
Combined firebox and heat pump system: Two of the biggest disadvantages to wood burning stoves is that firewood must be placed periodically into the stove, or it will go out – and that the heat is unequally distributed in the house. The first innovative stoves of the late 1970s partially solved the first problem by having adjustable air intake and flue dampers. Stove owners could stoke the stove full of wood and tighten the dampers before going to bed and night, in hopes that hot coals would remain in the morning. However, the damped stoves injected immense quantities of smoke and carbon monoxide into the air. If the occupants left for the day or the weekend, pipes within the house would freeze.
In a combined firebox and heat pump system, first developed in western North Carolina, the cold air intake for the central furnace is near the firebox. The air is circulated around the exhaust flue (metal chimney) of the stove before entering the heat exchanger of the furnace. Typically, metal fins are welded to the section of the flue within the cold air return to enhance the flow of heat from the flue into the duct. The fan of the furnace circulates warm air around the house. The heat pump will start operating, if the temperature of the air leaving the fan chamber is below that set by the thermostat.
A 3200 sq. ft. passive solar, house built near Weaverville, NC in 1986 was located in the shadow of a mountain all winter. This type of location traditionally insured enormous winter heating bills for its owners. However, it had a combined firebox and heat pump system. Two oak logs in the fire box would keep the house at 75 degrees F. when the temperature outside was in the 20s – without operating the heat pump.
Pre-heating of water: Households can also pre-heat water using wood heat. The simplest way to accomplish this is to first coil the copper pipe carrying the water supply around a non-insulated exhaust flue of the wood box, before it attaches to the water heater. In order to enhance heat exchange efficiency, it is typical for an outer sleeve or duct to be placed around the coiled copper pipe. Generally, the water, pre-heated by the exhaust flue, is sufficiently warm to negate the need for the electric coils of the water heater to turn on. However, any heat added to the water by wood heat equals less energy being purchased from the electric or gas company.
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