few weeks back, a reader contacted me with a concern
that the portable humidifier his daughter was running in
a bedroom could contribute to a mold problem, although
he had seen no evidence of one yet.
my household, we have run humidifiers in bedrooms
because, for example, one son suffered from croup-like
symptoms as a baby and the house we owned back then had
radiators and the air was very dry. I never saw any
evidence of mold as a result, but we had a leaky house,
so the ventilation appeared to deter growth.
current house is much, much tighter, yet as I write
this, with the outdoor air temperature 27 degrees, the
indoor relative humidity ranges from 30 percent (60
degrees) in the second-floor master bedroom to 34
percent in the first-floor kitchen (62 degrees). The
master bedroom formerly was the attic.
range puts my house below the 45 percent to 55 percent
that Philadelphia-based energy expert Hap Haven says is
the relative-humidity range he commonly finds in homes
with mold problems.
the typical house, such moisture can easily find
somewhere to condense, Haven said. That is especially
true if the attic is well-connected to the house and not
a 68-degree home with a 40 percent relative-humidity
level leaks that air into an attic, it will condense on
any surface less than 43 degrees, he said.
a 70-degree home leaks 45 percent relative humidity air
into an attic, it will condense on any surface less the
like those can easily be found in an attic throughout
late fall, winter and early spring, Haven said.
the Mid-Atlantic, the indoor relative humidity tends to
level off in the mid-30s (percent range) when you
air-seal a home properly," he said.
relative-humidity range we should strive for in our
houses to reduce viruses, bacteria and respiratory
infections is 30 percent to 60 percent, say the
Environmental Protection Agency and industry
keeping the relative humidity in the mid-30s is good on