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When a new load of wood is ignited, there will be a surge of heat from the stove. This heat
surge is welcome when the room temperature is a little lower than desirable, but not welcome
if the space is already warm. Therefore, each load of wood should burn completely so that the
space begins to cool off a little before loading. Letting the space cool before loading is one of
the secrets to clean burning and effective zone heating.
4.5.5 Controlling the Air Intake
Once the firewood, firebox and chimney are hot, air intake can be reduced to achieve a steady
burn.
As the air intake is reduced, the burn rate decreases.
This has the effect of distributing the thermal energy
of the fuel over a longer period of time. In addition,
the flow rate of exhaust through the stove and flue
pipe slows down, which increases the duration of the
energy transfer of the exhaust gases. As the air intake
is reduced, the flames slow down.
If the flames diminish to the point of disappearing, the
air intake has been reduced too early in the combustion
cycle or the wood used is too wet. If the wood is dry
and the air control is used properly, the flames should
decrease, but remain bright and stable.
4.6 Building Different Fires for Different Needs
Using the air intake control is not the only way to match the stove heat output to the desired
temperature in the house. A house will need far less heating in October than in January to
maintain a comfortable temperature. Filling the firebox full in fall weather will overheat the space.
Otherwise, the combustion rate will have to be reduced to a minimum and the fire will be smoky
and inefficient. Here are some suggestions for building fires suitable for different heating needs.
4.6.1 Small Fires to Take the Chill Off the House
To build a small fire that will produce a low heat output, use small pieces of firewood and load
them crisscross in the firebox. The pieces should only be 3" to 4" in diameter. After raking the
coals, lay two pieces parallel to each other diagonally in the firebox and lay two more across
them in the other direction. Open the air control fully and only reduce the air after the wood is
fully flaming.
This kind of fire is good for mild weather and should provide enough heat for up to four hours.
Small fires like this are a good time to use softer wood species and avoid overheating the house.
4.6.2 Long Lasting Low Output Fires
For a fire that will last up to eight hours but will not produce intense heat, use soft wood and
place the logs compactly in the firebox. Before reducing the air intake, the load will have to burn
at full heat for long enough for charring the surface of the logs. The flame must be bright before
letting the fire burn by itself.
Page 20
Figure 9: Air Intake Control
Installation and Operation Manual - Harmony 2.3
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