One effect from forced air systems is under-emphasized, and sometimes
mistaken for air dryness. Unless you have a very good filtering system,
such as the HEPA type or an electrostatic precipitator that is
maintained regularly, using the air that you breathe as your heat
transfer medium is prone to distribute dust and keep fine dust in
suspension. The smaller the dust particles, the harder they are to
filter out, and the longer they will remain in suspension. Dust
particles can cause throat and lung irritation, and this sensation can
be (and probably often is) mistakenly assumed to be "dry air". For
example, when you wake up in the morning in the winter and your throat
is "dry" - a sensation that most of us have experienced in some of the
houses we have lived in.
We've had some discussion on this list in the past, and people have
described their personal experiences, including how humidification has
solved the dry air problem in their house. I'm sure that many of these
observations are accurate. It would be useful, though, to figure out how
to differentiate between the two different causes (dust and low R.H.) of
a similar effect, namely the sensation of dryness. This will be
complicated by the fact that two different individuals might have
different levels of sensitivity to both dust and dryness. A further
complication is that remedial measures for dryness can also be effective
against dust, since dust particles have shorter settling times with
higher R.H. In other words, you may think you have a dryness problem and
that you have fixed it with a humidifier when actually you have a fine
dust problem that you have, in fact, fixed with the humidifier.
A good test case might be a sensitive individual who lives in a house
with both a radiant heating system and a forced air heating system run
with, and without, a HEPA filter.
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Norbert Senf email: mheat@mha-net.org
Masonry Stove Builders mheat@hookup.net
RR 5, Shawville website: http://mha-net.org/msb
Quebec J0X 2Y0 fax: 819.647.6082
voice: 819.647.5092
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