OK to have RH 45% in cold climate?

Old 01-05-08, 04:27 PM
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OK to have RH 45% in cold climate?

I have been following a thread in a piano owner's forum I look at. Relative humidity is a big deal to piano owners since fluctuations of RH lead to tuning problems and possible structural damage to a piano if they are severe enough. There is a company that makes humidifier/dehumidifier systems for pianos, complete with humidistat, water tank, heater bars, etc., and it is set for RH of 42%.

Someone posted that they use a room humidifier to keep their piano room about 40-45% in the winter, and this is in a cold climate. I posted that I would be concerned about condensation in the walls, possible mold damage, etc. and wouldn't recommend keeping a room with outside walls that humid in a cold climate. Several wrote in to say that they have been doing this for years but no noticeable damage to their homes.

Any thoughts on this?

Old 01-05-08, 06:45 PM
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Humidity levels are best maintained at 35-55%. Piano manufacturers tend to recommend 40-50% humidity of for pianos. Temperature should be constant and not to exceed 70 degrees.

It's not so much the humidity level that is important. What is important is to maintain the humidity level at a constant year round. Wood expands and contracts as humidity and temperature levels fluctuate. The expansion and contraction can affect the piano.

Purchase a hygrometer (sold where thermometers are sold) and monitor the humidity. If humidity falls below 40%, you need to humidify. If humidity exceeds 50%, then you need to dehumidify. Again, the most important thing for piano owners to do is to keep humidity level at a constant year round.

Never place piano near or over or under a heat vent or near a heat source. If no inside wall is available, place piano away from outside wall. Six inches minimum will provide an insulating air space. Protect piano from the heat of sunlight. Insulated draperies will help protect piano.

Learn more about the effects of temperature and humidity on pianos and humidifiers at: http://www.beethovenpianos.com/tuning2.php
Old 01-05-08, 07:42 PM
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As far as effects on building materials "It's not a problem unless it's a problem". At home inspects in my Chicago climate you can certainly see problems at 50% RH in cold weather, for example I recently saw an example were condensation on the only single-pane window in the house had been sufficient to severely rot out the window sill below during the seven years since the house was built.

As for more widespread problems, sure, you can get them, but again the extent depends on many factors.

For example in my climate if 70F 50RH air is infiltrating into an attic, I would expect to see sheathing damage and perhaps mold growth on the north side, while the south side could be in pristine condition, here's a recent example:

North side of attic

South side of same attic
Old 01-05-08, 07:43 PM
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It depend on where or the temps you call "Cold Climate".

There are some homes that just luck out with a higher humidity! I know my home would not make it that high! That's why I have an outdoor sensor on my humidifier.. When it starting to get below 25, house is less than 40%, and as low as 25% when it's 0˚ out, it was higher, the windows would be dripping wet.

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