Kate and Phil Smith on sat 14 mar 98
A key issue in installation of a ventilation system, in this case an
exhaust system may be the atmospheric pressure relationship with any
other combustion appliances and with any other exhaust fans within the
home.
It is quite easy for a home to be depressureized leading to a backdraft
or down draft within a flue to relieve the suction. We percieve
leakyness in houses but our perceptions do not match reality.
This problem is worse in summer for a driving force "working the flue"
temperature difference, is gone. A negative pressure of 3 pascals(-3pa)
will cause a down draft in a typical water heater in summertime.
"Ah, waterheaters they dont run often" is a common response among the
trade.
Water Heaters have been found to go from producing 20 ppm Monoxide to
2-3,000ppm monoxide in seconds. A Building Scientist I know had one go
to 10,000 ppm. (What kind of reduction firiing is this gas kiln folks?)
Exposure above 15ppm will lead to a distortion of perception and its all
down hill from there.
If you take air out of your house you need to replace it. Dependent upon
the volume exhausted in a best case you may get by with a passive
opening, but you may need a power make up system.
Find someone to do a blower door test and as part of it a worst case
depressurization test to determine which way to go.
Phil Smith
White Bear Lake, MN
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