Eight Reasons Why Smoke
Enters Your Home:
(The main reason why smoke enters you home is a matter of
air-pressure phsyics covered by the section above: "How & Why
Chimney's Draft." Here are eight additional factors to keep in mind):
1) (The most obvious): Upon closer inspection, perhaps the damper is actually closed, and not open? Use a flashlight and poke your into the hearth enough that you can see the damper assembly.
Damper assemblies are mechanical, and mechanical devices malfunction--this is the only way to tell for certain that a damper is open properly.
Perhaps the damper is only partially open? This could allow some, but not
all, of the smoke to exit through the flue.
Is your chimney flue excessively dirty? Creosote deposits can cause a partial obstruction in the flue, just like plaque can clog a human artery.
Do you have a cap? Caps can prevent sudden down-shears that can literally push smoke down a flue and back into the house.
Caps also serve to interfere with direct wind, creating turbulence that permits smoke to escape the flue during high winds that would otherwise act as a lid at the top of the chimney.
Is your chimney tall enough? In order to draft properly, a chimney flue must extend up at least 10 or 12 feet from the hearth.
It is extremely difficult to reliably control the draft of fireplaces
with flues that are too short, since they are so susceptible to wind
gusts and sudden pressure changes.
Caps not only block out rain, but also interfere with heavy
winds that otherwise would create a shear effect, acting like a lid and therefore keeping smoke from getting out.
Is your flue large enough for the fireplace opening? The
rule of thumb is that the surface area of the fireplace opening
(width multiplied by height) can be no more than 10 times the area of
the flue opening at the top (the ratio is 12:1 for rounded flues,
including metal liners).
Flue opening that are too small will not
able to handle all the smoke, which will instead follow the path of least
resistance and go back into the house.
Because there is no practical
way to make the flue opening at the top larger, the only realistic
option is to make the hearth opening smaller by installing metal
smoke guards (a strip of metal placed on the top of the hearth that
reduces the size of the hearth opening).
Is your chimney on the outside of the house? If
you have a masonry chimney that is located on the outside of the
house, anytime it is cold outside the air inside of the chimney flue
will be as well.
Because cold air is dense, it will tend to sink down
the flue, rather than rise up, as warm air does. In
general, the temperature of the air inside the flue should be
relatively warm before efficient drafting can begin (ideally 200 degrees Fahrenheit or more).
For this reason,
outside-the-house chimneys can make it a challenge to start a fire, and may
cause some sporadic back-drafting until the fire heats up, and then once
again when the fire cools down.
A time-honored trick to get a fire
drafting well quickly is to light some rolled up newspaper, and hold
it near the flue opening (or even extend it directly into the flue,
perhaps with the thongs that come with your fire place tools). This
will heat up the air in the flue enough to jump-start a draft.
Is your home too tight? Modern homes have increasingly been
made airtight (with gasket triple-seal windows, millimeter-precise
door fittings, and modern insulation).
That is fabulous for energy
conservation, but it makes it much harder for a chimney or wood stove
to quickly replace the air that drafts up the chimney during a fire.
The result? Fireplaces will burn sluggishly, burn-out early, or cause
smoke to enter the living area.
Oftentimes the only option to
facilitate good drafting during a fire is to open just a crack any
window or door that is as close to the fireplace or wood stove as possible (and which, ideally, faces the wind).
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