SB: Air supplies

[dfugler@cmhc-schl.gc.ca]

David,

You have been getting good advice, in my opinion, from Norbert and Rob. If
you want a scientific report, CMHC published something called Fireplace Air
Requirements in 1989 that dealt with different fireplace air supplies and
their effects at isolating the fireplaces from depressurization. You can
order it 623 748-2367 or, if you are Canadian, phone 800 668-2642 and they
will send it for free. The five fireplaces tested were all metal, factory
fireplaces, but the air movement characteristics could equally apply to
masonry.  Basically the research showed the amount of air that entered
through intakes vs the amount of air required by the fireplace and chimney.
Having an air supply to a fireplace does not isolate the fireplace from the
effects of house depressurization. If you have a big fan operating in the
house, your fireplace is at risk at the diedown stage whether or not you
have an air supply to the fireplace.

As far as house air leakage, the testing standards in the US are:

1. ASTM. 1999. ASTM Standard E779-99, Standard Test Method for Determining
Air Leakage Rate by Fan Pressurization. Philadelphia, PA; American Society
for Testing and Materials..

2. ASTM. 1997. ASTM Standard E1827-96, Standard Test Methods for
Determining Airtightness of Buildings Using an Orifice Blower Door.
Philadelphia, PA; American Society for Testing and Materials.

I have a great deal of confidence that these tests can provide you with a
measure of building airtightness which will help you to assess ventilation
requirements. However, I use the same analogy as Rob Tom - "try blowing
through stucco" - to convince people that straw bale houses do not
"breathe" through the walls. If you want decent ventilation then, you have
to rely on leakage through other house components (i.e. flaws), or open
windows, or install a ventilation system.

Don Fugler
CMHC Research


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