Fireplace & Woodstove Indoor Air Quality Improvement Guide InspectAPedia® -
INDOOR AIR QUALITY IMPROVEMENT, KEY STEPS
Removing or keeping out indoor contaminants
Home ventilation strategies
Best methods for cleaning & filtering indoor air
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Traditional open fireplaces
and older leaky woodstoves burn very inefficiently
and produce hundreds of chemical compounds, including
carbon monoxide, organic gases, particulates, and some of
the same cancer-causing agents found in tobacco smoke.
Minor spillage of these pollutants occurs regularly, primarily
when starting or stoking the fire. However, the larger
concern is when the fire smolders late at night, producing high levels of CO and a weak draft. Backdrafting at this
time can be dangerous or even fatal.
Another problem, particularly with fireplaces, is created
when the fire is roaring and drawing up to 400 cfm of
combustion air. At this point, its voracious appetite for air
can cause backdrafting in other combustion appliances
such as a gas water heater. Also, the need to reheat all the
makeup air drags down the fireplace’s heating efficiency
to less than 15% and, if the fireplace is allowed to smolder
all night, it becomes a net heat loser.
Woodstove efficiency has improved dramatically in
response to EPA emissions standards (begun in 1988 and
updated in 1990), which apply to most freestanding wood
stoves and to fireplace inserts with air-supply controls and
tight-fitting doors. To meet these standards, manufacturers
use either a catalytic converter, similar to the ones used in
cars, or a reengineered firebox. The new fireboxes have
primary and secondary combustion zones capable of
reaching system efficiencies of 60% or more and reducing
combustion air intake to as little as 10 cfm. If installed
with an outdoor air supply, these can be successfully de-
coupled from household air pressures.
While many fireplaces are fitted with glass doors, and
some have outside air intakes, nearly all of the glass doors
leak air. Even with low levels of depressurization, these
fireplaces can still backdraft, and the fireplace’s outdoor
air supply might become the makeup air for the kitchen
range hood or other exhaust fans, drawing fireplace fumes
along with it. The best solution is an airtight fireplace
insert.
To minimize pollution, indoors and outside, from wood-burning appliances
Choose a properly sized stove or insert certified as meeting EPA emissions standards.
Make sure the door gaskets are in good shape, the doors fit tightly, and the stove is free of air leaks.
Make sure the flue is the correct diameter and height,
and have it inspected and cleaned annually.
Use wood that has been split and dried for at least six
months. Try to use small pieces, and do not overload
the firebox. Leave enough room for air to circulate
freely around the wood.
For safety purposes, install a smoke alarm and carbon
monoxide detector in the same room as the woodstove
or fireplace.
Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education.
Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com.
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