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MMD > Archives > January 2001 > 2001.01.19 > 09Prev  Next

Relative Humidity and the Piano
By Cecil Grace

I do not have any pianos here yet (they are being restored) but I am
working to get the humidity under control in this large steam-heated
house with no air conditioning and no ducts.  Although I have much to
learn, I thought I'd pass on some information that MMD readers may find

Mr. Vanderhoofven mentions Radio Shack hygrometers.  I have several of
these, and get all different readings.  I also have one from Bionaire,
which may be a little more accurate.  However, I would recommend using
a wet and dry bulb psychrometer to calibrate them.

He also mentions humidistats.  An excellent one is available from an
electronic surplus house, Herbach and Rademan, of 16 Roland Avenue,
Laurel NJ 08054-1012.  It is their catalog no. TM89HVC5203, and only
costs $4.95.  (However there is a processing fee of $5 unless your
order is for $25 or more, so you may want to order other things from
their catalog, which is available by mail or online at  The humidistat has a double-pole switch, so you can
connect it either to open or to close on rising humidity.

In summer, I use four dehumidifiers, all controlled from one
humidistat, using X-10 controls that send signals over the power lines.
These are available from Radio Shack (which calls them Plug 'n Power),
Herbach and Rademan, and other suppliers.  I leave it to electronics
professionals or hobbyists among your readers to work this out, for the
way I did it would take to long to describe here, and in any case
cannot be duplicated because I used surplus parts, some of which are no
longer available.  Basically, I put a "Sundowner" controller (which
contains a photocell) in a light tight-box, and used light bulbs to
control the system.  (For skilled engineers, there are better ways.)

One thing you must consider in your design is power outages, for the
humidistat may switch over when the power is out.  Your system must
resynchronize itself when power returns.  I also included a timer to
silence the noisy humidifiers for up to an hour when I want to listen
to music, and then turn them on again, which I often forgot to do
before I built this system.

Perhaps one of your subscribers would like to make such a system for
sale to piano owners, or a kit to build it.

In winter, I use four of the largest Bionaire humidifiers, each with
three large water reservoirs.  The problem is that refilling the 12
reservoirs is such a chore that it does not get done when it should.

I would like to get some humidifiers that refill automatically from the
plumbing supply.  Bionaire used to make them, but no longer does so.
If anyone can tell me where I can obtain new or used ones, I would
greatly appreciate it.  Naturally, they should have overflow pipes,
to avoid the flooding that some or your contributors described.  These
would be connected to the same tubes used to drain the dehumidifiers in

I don't know whether this will help anybody, but hope it will.

Cecil Grace

(Message sent Sat 20 Jan 2001, 00:43:43 GMT, from time zone GMT-0500.)

Key Words in Subject:  Humidity, Piano, Relative

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