Introduction: An Easy-to-make, Energy-saving Piano Humidity Control System (dehumidifier)

Picture of An Easy-to-make, Energy-saving Piano Humidity Control System (dehumidifier)

In this intructable, I'm gonna show you how to build a simple dehumidifier for your precious piano, at a fraction of cost if you buy a similar product. And it uses much less energy than a room dehumidifier does.

We bought a new piano last year for my son. When the tuner came for his first service, he told me that the best humidity level for a piano is 42% to 45%, and he recommended us to install a piano humidity control system - Dampp-Chaser. Their website has an excellent description of the benefits of this system.

I won't repeat all the benefits here, but just in summary:
- stabilizes piano tuning, so you can see your tuner once a year or even longer, instead of every 6 months. This saves you about $100 a year.
- save hundreds of $$$ a year compare with using home dehumidifier

But the cost is over $600, and maybe up to $900 to have it installed!!!

I've used the last penny for the new piano, but the Dampp-Chaser seems promising. So I decided to make my own one.

Stay turned. Here comes my design.

Step 1: Design

Picture of Design

First of all, this system is for acoustic pianos. If you have an electronic piano, never mind. You'll never need tuning, so you don't need it. And it's for upright pianos. I don't have a grand piano to play with.

As looked into the Dampp Chaser system, I decided to get rid of the humidifier part, just to make the dehumidifier part. To avoid to be too boring, I put all the detailed descriptions and explanations in the last step. Find them there if you are still interested.

Therefore my humidity control system is actually a dehumidifier - to be used in summer time to keep you piano not too humid inside while you can also be comfortable outside in a room.

Here's what the system will consist. It's really simple.
- a humidity sensor to sense the humidity inside of the piano
- a heater inside the piano to reduce the humidity when needed
- a RH controller to control the heater

See attached pics for my design. And you can also download the attached pdf file for the complete design that includes dimensions the parts you need to make.

Step 2: Materials and Cost

Picture of Materials and Cost

Here's the materials list:

QTY Description

1 Thermostat with RH display and control

1 120/12/24VAC, 12VA transformer

1 24VAC relay with socket, 3SPDT, 5A 120VAC contacts

4 100W, 120VAC incandescent light bulbs and socket base

2 IN4001 diodes

1 25V 22uF capcitors

2 12VDC, 1.4W brushless electric fan

1 16x48" zinc coated sheet metal for heating duct

1 2 pair shielded cable, 6' long, 24 AWG

1 1 pair shielded cable, 6' long, 24 AWG

1 power cord with plug, 6' long or as needed.

8 Terminal blocks

AR some other scrap wood blocks and plates

The total cost would be less $100 if you have to buy everything, but if you could use something from your stock or scrap, it could be much less, in my case, just $31.24. See the attached file for the details of the materials and cost estimate and my actual cost.

Tips: The Thermostat is the most costly thing here. I bought one from Canadian Tire when it's on sale with more than 50% off. Usually the sale season for thermostat is just before winter.

Step 3: Make the Heater

Picture of Make the Heater

After I had all the materials, I started to make the heater first.

1. Make the heater base. I just cut all parts according to the dwgs and screw them together. There's no much room inside of a piano for you to play with, so measure it and adjust the dimensions if necessary before you actually make it.

2. Mount the light bulb sockets. This was a hard part, because I couldn't find the small round sockets as shown on my design. I had to buy the 6" round sockets and cut them into approx. 3x4". I screwed the sockets to a wood block and use a tablesaw to cut them. I would never do it again, if I can find smaller sockets, even pay more for it.

3. Mount the relay and transformer. This was easy.

4. Mount the terminal blocks to the bottom of the base. 2 for the incoming 120VAC wire. 2 for the control from the thermostat, and 4 for the rectifier circuit for DC fans.

5. Wire all components so far.

5. Attach the support frame for fans and heat shield. secure the fans to the frame ( I just used tie wraps)

5. Wire the fans, and after that install the heat shied. Remember to connect the ground wire to the shield.

6. Screw in light bulbs and test. Haha!

Step 4: Hack the RH Controller (thermostat)

Picture of Hack the RH Controller (thermostat)

Now it's time for our thermostat to give birth to her sensors.

*** CAUTION: Before and occasionally during this procedure, touch a metal faucet or water pipe to discharge yourself.

1. find the sensors - the thermistor is usually a tiny beard, and the humidity sensor is flat. You should be able to see them though the small openings on the back.

2. Take the thermostat apart. Remove the sensors and solder the wires in. Drill a extra hole on the PCB "ground" to connect the drain wire of the sensor cable. Save the sensor to make the sensor plate in next step.

3. Find the terminals for humidity control. Connect the control cable.

4. Close up the thermostat. You may need to drill two holes at the bottom to route out the two cables. The mother thermostat can have a rest now.

Step 5: Make the Sensor Plate

Picture of Make the Sensor Plate

Let's take care of our two little babies now. A 0.75x1.5" plate would be good enough to cradle them. Connect them to the other end of the sensor cable. I also give them a cover. Done!

Step 6: Install

Picture of Install

Now it's time to put the whole system in place.

1. Mount he humidity controller (thermostat) on the wall wherever you like.
2. Remove the foot board of the piano, and seat the heater in.
3. Find a good place to place the sensor sibling. I attached them to the support metal arm of the piano. Tie wrap cables to the arm and pedal wires where suitable.
TIPS: I used nothing other than tie wraps inside the piano. In case you need to call the manufacturer for warranty issues, you can remove the entire system without any trace.
4. Check and test the connection.
5. Put the foot board back, and route cable out from the gap (about 1") on top of the foot board.
6. Oh, I almost forget. Set the humidity setpoint to 45%.

Now plug in and you're all done!

Step 7: Results

Picture of Results

It's raining today. My room thermometer shows 60% of humidity. Plug in the system, and here you get 45% in side! (with 4~5 degree C increase) cycle is about 1:4 (23s ON / 96s OFF), keeping the humidity between 44% to 45%.


Step 8: Q&As and Design Considerations

Picture of Q&As and Design Considerations

Q: Why do you just make a dehumidifier instead of a complete system that includes humidifier?
A: Resons are:
- It's scary to me to bring water into a piano.
- It makes this project much easier and cost much less to complete.
- The only time the humidity is too low for a piano (<40%) is winter - when the furnace heats your house up. This is fine in my case, because I have a humidifier for the whole house to keep the humidity level at around 40% in winter. Nevertheless it's very uncomfortable for me to stay in an environment where the RH is less than 40%.
- Summer time is another story. The humidity can easily go over 80%. You can use your A/C or room dehumidifier to remove moisture when the humidity is too high. However, I'm (and I think most people are) very comfortable when RH is around 60%, until the humidity is over 70%. So it makes no sense to bring the whole room down to 45% by using electricity tigers - A/C or room dehumidifier.

Q: How it works?
A: The relative humidity will drop by a factor of 2 for each 20�F(11�C) of absolute moisture. So even the RH is 90%, we'll bring it down to 45% to suit your piano by increase the temperature up to 20�F(11�C) . Check more out here:


miguel.rey.9889 (author)2015-03-22

This is basically works the same way as the DC. I think much easier to just purchase a Moisture King humidistat and a couple of gun safe ceramic heating rods (same used in the DC) also sold by Moisture king. Cool thing about the Moisture King is it's adjustable depending on your area and you can also plug in a humidifier to hit that will cycle on off according to the RH. Fraction of the cost of the DC since they don't sell parts to the general public

martyjandrews (author)2014-07-10

I can't seem to find any reasonably priced thermostats with RH control. Can you tell me what model NOMA you used? Thanks!

fbartlett (author)2011-04-01

The design is straight forward, but the heating elements could be replaced with a more efficient heating source. Got any better ideas? The retail ones just use a 15 watt electric heating element to do the job, so why use 400 watts of IC bulbs? It would dry it out really fast but do you need that much heat?


Taotaoba (author)fbartlett2011-04-01

I use 4x100W bulbs, but please note that two bulbs are connected in series and then in parallel. Therefore each bulb will work on 25W (approx.), total power is only 100W. The reason to do it this way is to bring down the temperature of the bulbs.

I don't know if the 15W will be enough, because my calculation sugguested 50W. With 100W, I can get some "engineering margin", and the heater doesn't have to work that hard. In really humid days (>70%), it works on 80-90% duty.

This system has been in service for my piano since then, and it really does it job, keeps my piano in good shape. Cheers!

keniris (author)Taotaoba2011-11-08


I have just bought a baby grand and concerned to use a system for humidity control. I note several articles mention using heat to control humidity.
Having taken weather courses (I have a sailboat) heat increases the amount
(percentage) of moisture in the air. Can you explain how a heater reduces humidity. A dehumidifier uses a refrigeration unit to decrease humidity.
In Ontario, Canada, our summers are very humid, and winters very dry, so we need a system to both moisturise and, remove moisture. Perhaps I'm misunderstanding something but at this moment a bit confused.
Would you explain for me please how heat decreases humidity?

lilycjwang (author)2009-10-26

Very good idea and clear instructions. i might ask my husband to build one for me.

Myself (author)2009-06-14

Cool, that's the third nontraditional use for incandescent lightbulbs I've come across recently. They're easy to work with, aren't they? How do you feel about the cycle length of roughly 2 minutes? It seems like the relay and bulbs might not last too long, being operated so frequently. But if you slow it down (by partially enclosing the sensors?), it would mean the wood in the piano would "feel" the fluctuations more. Suppose you had four humidistats, each connected to its own heater, and made their setpoints 40%, 42%, 44%, and 46%, or so? You could probably find an equilibrium state where the appropriate number of bulbs ran constantly, relays operating only when the room's humidity changes.

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