50 | February 2020
We target 30-40% RH in winter, enough
to prevent nosebleeds and static shocks,
but generally pretty safe for condensation.
We'll come back to this when we discuss
humidifiers.
For now, note how the 30-50% range
is very important to minimize a lot of bad
things in your house. At a minimum stay un-
der 60%.
The Elephant in the Room —
The AC ain't running!
AC tends to be the big dehumidifier in most
homes. There's a huge problem though,
when April showers and May flowers are
here, is the AC running? Or on those lovely
fall days at the end of summer that are still
warm, but the ground is still wet? On those
70 to 75-degree days is the AC going to be
on? Probably not.
But there is a lot of humidity to remove,
right? Absolutely.
That brings us to the elephant in the
room: there is no way to control humidity
with your air conditioner on days like this.
Days like that are getting more and
more common, average dew points are on
the rise as I explored in my The Coming
Mold Explosion video. Here in Cleveland
we have 3-4 months per year of conditions
like this, many "green grass" climates
have more!
Shoulder Seasons — The REAL
Danger Zone
Remember those 40 Foobots we have in
the field? They've taught us a lot. Here's
a Foobot dashboard chart from one cli-
ent home where we performed insulation
and air sealing upgrades but have not yet
touched the HVAC.
The answer? About half the time. There
is a fairly high risk that something bad is
happening in their home.
There's a better metric to look at it
though, called dew point. Dew point is
the temperature that relative humidity hits
100%. It varies from moment to moment,
but unlike relative humidity you only need
to know one number, the dew point, where
This chart is the entire month of September 2019, the home is in Cleveland Ohio.
How much of the time was his humidity above 60%?
The answer this time is almost never, the dew point was higher than we like to see
the entire month of September 2019.
