How to heat with wood?

Proper heating with wood is essential for reducing the risk of fire and achieving significant financial savings.

Here are some important considerations and steps to follow:

Chimney maintenance: When was the last chimney sweep? Ensure that your chimney is regularly cleaned and inspected for any cracks or damage. Chimney sweeps recommend having the chimney swept twice a year instead of just once, as it helps save the equivalent of two rooms full of trees.

Proper fuel selection: Be cautious about what you put under the stove. Over his long-term experience, Madis Mäe, the master chimney sweeper of Saaremaa, has come across various items that should not be burned, such as tetrapacks that produce combustible pitch, films that emit toxic smoke, plastic bottles that generate chlorine compounds and corrode the chimney, as well as non-combustible materials like glass, foil, cigarette packs, and children’s diapers. In one instance, he discovered 17 buckets of wood chipper waste in a chimney leg, which resulted from long-term neglect rather than burning.

Air supply: Proper heating requires sufficient air circulation. To achieve a high combustion temperature, ensure that the fireplace receives enough air. Grate hearths, stoves, and some ovens have separate sliding doors under the hearth, which should remain open throughout the combustion process. Furnaces and fireplaces without these separate doors receive air through the air door and the outer door of the hearth, which should be fully open at the beginning of heating. The damper should be completely open during the entire heating process. It’s important to note that a common misconception among housewives is to heat with a half-closed damper, thinking it prolongs the burning and provides more heat with the same amount of fuel. However, in reality, incomplete combustion occurs when the damper is half closed, resulting in soot buildup and increased fuel consumption.

Calling the chimney sweep more often: It is advisable to have the chimney sweep called more frequently to ensure proper maintenance and minimize potential issues.

Avoid wet fuel: Burning wet fuel, such as wood with high moisture content, is inefficient and leads to the formation of pitch in the chimney. Approximately 70% of the heat is wasted in the chimney due to the need to evaporate the water. A stove full of wet wood can contain up to 8 liters of water. The water vapor and soot released during incomplete combustion can settle on the cold flue surface and create pitch. It is recommended to use air-dry wood, which provides 80% more heat compared to wet or raw wood. Ensure that the hearth receives sufficient airflow, especially at the beginning of heating when the smoke passages are cold, to reduce moisture and pitch formation.

Proper use of the oven: The oven acts as a heat accumulator, storing heat and gradually releasing it into the room. By heating the oven or stove correctly, you can save 20-30% of fuel and extend the lifespan of the appliance. Follow the steps mentioned earlier to ensure proper heating.

By following these guidelines, you can heat your home effectively, minimize risks, and optimize the use of wood as a fuel source.

In a closed hearth oven, the damper is fully open during combustion. In a stove with a closed hearth, the hearth must be cleaned of old ash before heating because the heating material can accumulate inside it and not burn properly. In the front of the hearth, ignitable materials such as paper, sticks, and rags are placed. Finer kindling is placed on top of them, followed by coarser pieces. It is more beneficial to choose shorter sides, around 40-50 centimeters long. Very thin slices will burn quickly, and the oven will not have enough time to heat up. The average diameter of the firewood logs could be 10-15 centimeters. Conifer wood can be slightly thicker than birch and alder, and dry wood should be thicker than wet wood. The firewood logs should be placed as close as possible to the mouth of the hearth, leaving the rear part of the hearth about a third empty. If the logs are very short, around 20-25 centimeters, they can be arranged in two rows behind each other, with the thicker and wetter logs at the back.

When the logs are ignited, the draft door is closed, while the front door remains open initially. At the beginning of the heating process, the flues are still cold, and when the logs burn, water vapors and tars are deposited on the flue walls. After about 10-20 minutes, when the fuel is burning intensively (with yellow flames directed upwards and a characteristic rumbling sound from the furnace), the front door can be closed partially, leaving a gap of about 10 centimeters. At this point, an additional log can be added to the front of the hearth. The oven will heat up over the next one and a half to two hours. Towards the end of the heating process, it is advisable to further reduce the gap in the front door to about half a finger’s width. The front door should only be closed when the flame is no longer visible, and only glowing coals remain in the oven. Important note: the damper should remain fully open throughout the entire burning time and can only be closed about twenty minutes after closing the oven door. However, if the front door and damper are left open for too long after the heating is finished, the heat will escape through the chimney.

A stove with a grate hearth receives air through the ash chamber and the grate. In an oven with a grate hearth, the ignition materials are placed beneath everything on the grate: paper, straws, and kindling. Then finer and drier pieces are added, followed by coarser and moister ones. Once the wood is fully ablaze, the hearth door is completely closed. The hearth receives air through the ash chamber and hearth grate. If the grate is absent and the damper is open, the fuel will burn completely. Closing the ash chamber door and later the damper creates a closed hearth stove. Such stoves tend to accumulate more soot in the flues. In stoves, the path of flue gases from the hearth to the warm wall and through the flue to the chimney is relatively long, while the temperature in the hearth is lower compared to the oven. Consequently, more soot and residue accumulate in the flues of the stove. However, the primary source of this buildup is incorrect heating. Proper draft is essential. If the hearth is obstructed, the ash chamber beneath the hearth becomes filled with ash, and closing the damper halfway results in the formation of pitch in the flues. If the fuel is still wet, and therefore the temperature is particularly low, water vapor and tar substances will deposit on the flue walls more significantly. Therefore, it is important to empty the ash chamber and clean the hearth before heating. However, during heating, the damper should be kept fully open.

Let me provide another cautionary example regarding the impact of humidity: burnt-out frying pans. In some households, apples, wet clothes and shoes, and even firewood are dried in the oven. And then they wonder why the furnace is rusted from the inside, not burnt from the outside, as chimney sweeper Madis Mäe explains.

Preheating is helpful when starting with a cold oven. It should be emphasized that poor draft lowers the combustion temperature. If the heating is done with the oven door closed or with the damper only half open, the gases move slowly in the chimney, cool down faster, and deposit in the flues. If the oven has not been heated for several days, it cools down to an extent where the draft diminishes. Preheating the chimney flue can help with this by starting a small fire in the hearth, for example, using only paper. Sometimes burning paper is inserted into the chimney flue through the soot hatch, although this practice is not recommended. If the chimney is not cleaned, the soot and pitch can catch fire.

Excessive air is also detrimental to the oven. Air that does not participate in combustion passes through the furnace flue, unnecessarily cooling its inner surface. Therefore, the draft and outer door of the hearth should not remain fully open throughout the entire heating period. Instead, the draft door should be closed as soon as the fuel is completely ignited, while the outer door should be closed. Simply opening the draft door reduces the temperature in the hearth by several hundred degrees. However, having excess air is less harmful than heating with a half-closed damper. It is better to allow more air into the oven rather than obstructing it with a damper or closing the oven door completely.

Overheating can damage the oven. One of the typical mistakes is overheating, which often occurs in winter in country houses and cottages that are rarely visited during winter or in extremely cold weather conditions. The room is cold, the oven is cold, and putting firewood in the oven doesn’t help immediately. Then, as the process continues, the oven becomes slightly lukewarm. Finally, when more firewood is added, the oven breaks. If the oven has not been heated for a while, the heat does not reach the outer surface as quickly. Therefore, it is important not to overload the oven with too much fuel at once. In this case, the inside of the oven heats up faster than the outside. Since the stones expand unevenly when subjected to intense heat, this can cause the furnace to crack.

If the fuel does not burn completely, it produces combustion byproducts such as smoke, soot, and pitch. Smoke is composed of various vapors, tar particles, resin, grease, and tiny coal particles. The smaller the coal particles, the longer they remain suspended in the air. The color and odor of the smoke depend on the burning material. Master chimney sweeper Leo Kalme possesses the ability to identify the type of fuel being burned solely by examining the smoke. When burning wood, the smoke appears as a greyish-black color. Paper, hay, and straw produce whitish-yellow smoke that can cause eye irritation. Burning cloth results in brownish smoke with a bitter smell. The smoke from rubber and petroleum products is dark black and possesses a distinctive odor. These fumes, which may taste bitter or sweet, often pose a hazard. Therefore, it is advisable to periodically monitor the smoke emitted from your neighbor’s chimney, particularly in densely populated areas. Let’s establish a “neighborhood watch” for this purpose!