With all of the frigid air that has descended upon many areas of the US
over the past few weeks, I would like to bring up the potentially dangerous
issue of maximizing indoor humidity levels when outdoor temperatures are very
cold.
Has anyone seen the following warning from the American Society of
Heating, Refrigeration and Air Conditioning Engineers, that comes with
room-sized or heating system humidifiers?
" Do not exceed these following humidity levels when the outside
temperatures are less than those stated for each humidity level"
Has anyone seen the question and answer section from a Sears
installation instruction booklet for their heating system humidifiers? A
section from this is quoted later in this post.
What I'm talking about is that if one's intent is to bring up the
humidity level in the piano room during the cold months, then all of the
humidifier manufacturers and re-
tailers and the American Society of Heating, Refrigeration and Air
Conditioning Engineers (ASHRAE) provide very specific instructions that urge
that the humidity level one should
attempt to attain be limited when outside temperatures are below 30 Degrees
F. They are universal in this regard and say that humidity levels above the
following should not be
attempted given the following corresponding outdoor temperature levels:
Outdoor Temperature OK Humidity Level
Degrees F. % RH
+30 40
+20 35
+10 30
0 25
-10 20
If the 40% RH is to be maintained in the winter so that the RH spread
from winter to summer is minimized, then it really needs to be done within
the piano itself. Of course
there are exceptions, the obvious being where temperatures don't go below 30
Degrees F. or don't do it long enough for moisture to condense and freeze
within the wall. The most significant other exception is in newer homes
where a moisture barrier (plastic sheet) has been added to the wall during
construction.
Aprilaire publishes a marvelous booklet on humidity with a sectione
entitled "What Indoor Relative Humidity is Correct" and if anyone would like
information on this, please get in touch with them, or call and we'll send
you their address.
Aprilaire has further begun to make a humidistat that changes the
humidifier setting to automatically compensate for changing outdoor
temperatures.
Sears provides a question and answer page with their installation
instructions. One of the questions with the Sears response follows:
(6) What is the safe humidity level for my home?
" In order to determine the safe relative humidity for homes exposed to
various low outside temperatures, NESCA (National Environmental Systems
Contractors Association) conducted tests and published recommended humidity
levels for various outdoor temperatures. These are shown in the chart below.
These levels help prevent damage to your home such as water running down the
walls or even building up inside the walls. The safe indoor relative
humidity percentage is not a fixed number but will increase or decrease as
the outdoor temperatures rise or fall.
Outside Maximum Safe Recommended
Temperatures Indoor Relative Humidity
-10 Degrees F. 20%
0 Degrees F. 25%
10 Degrees F. 30%
20 Degrees F. 35%
30 Degrees F. 35%
I could add quotations from a number of other sources voicing the same
concern but won't in the interest of brevity.
Bob/Gayle Mair
Damppchasr@aol.com
This PTG archive page provided courtesy of Moy Piano Service, LLC