I have been using the Honeywell HCM-6009 humidifier for one year to increase the relative humidity in my apartment during winter. Here is my review of the device and the improvements I made over time to make it more tolerable.

Review

I needed a humidifier that can pump a lot of moisture in the air, has a large water capacity to run at least a day without filling it, is easy to clean, has an hygrostat and not too noisy. The Honeywell HCM-6009 seemed to fit the bill. This device works by evaporating water from a wicking filter using a fan. Initially I wanted to use an ultrasonic humidifier, but I have hard water at home and I was worried that I would have to clean white dust all the time.

After one year of use, I have mixed feelings about this humidifier. On the positive side, I love the design of the water tanks. In total, they contain 3 gallons of water (around 12L) separated equally between two tanks. This amount of water is enough to last more than 24 hours. Also, the tanks are used sequentially, i.e. one tank is emptied before the second starts being used. This way, you generally have to fill only one tank per day, not two half tank per day.

Even on the slowest fan speed setting, the humidifier generates a lot of moisture quickly, so it doesn’t have to run continuously. The last positive point is the hygrostat. It is a mechanical device, not electronic. The lowest setting is around 35% relative humidity. It is not super precise, but more than enough to keep the room humidity within around 5% of the desired humidity.

Then, there is the major problem with this device : noise. A series of questionable design decisions have created a device that is much noisier than necessary. The first source of noise is the generated wind. There are three fan speed settings. The slowest is reasonable, but the two others are much too fast. The slowest setting generates more than enough air, I don’t see the use of the faster settings.

Then, the impeller was not properly balanced. It might be a defect that affects only the one I bough, but after opening the device, I see no effort to balance it, so I feel that a lot of HCM-6009 in the wild must be out of balance.

The final noise source is probably the most irritating : humming. The second the motor is turned on, there is an audible electrical humming noise. To give you an idea, here are two samples of noise coming from the device. The first sample is recorded about 5 cm away from the air vent:

The second sample is recorded at the top of the device to isolate the humming noise:

Generating the sound spectrum of each sample, we get the following graphs :

On the first one, we get a wide spectrum noise typical of wind noise. On this graph, we also see a spike around 120Hz. On the second graph, where mostly the humming is recorded, we clearly see the 120Hz spike. This is indicative of noise coming from the AC motor, since it is the second harmonic of the 60HZ AC signal used here in Canada.

The way the motor is attached to the device makes the problem worst by amplifying the 120Hz noise. The motor is held by the thin plastic cage containing the vents to let the air in and out. This cage has a tendency to resonate at this frequency. Then, the whole assembly is made of thin pieces of plastic that overlap each other and transmit and amplify the noise. While I was disassembling the device, I realized that the AC motor run capacitor is hanging loose and touches the outer wall of the device. The outer wall vibrates at 120Hz and “hits” the capacitor at this frequency, generating even more noise.

Improvements

Most improvements I made were done to reduce the noise. The first I did was placing some foam pads at the bottom of the main cage (the one that holds the fan and motor). The goal was to eliminate the transmission of noise from the cage to the base. It was not very successful.

Then, I balanced the fan by sticking a dime with blue tack on the fan. This helped reduce the noise caused by the fan vibration. When I disassembled the humidifier, I moved the balancing dime to the top of the fan since there is more surface to put it and it is easier to get a good balance.

Then, I added mass to the sides of the cage to dampen the vibrations (mostly the 120Hz humming). I used 2$ coins and blue tack. I moved a finger across the wall of the cage I tried to find the places where I felt the stronger vibrations. It did help a little to reduce the humming.

The final modification was to add a piece of foam in the space where the AC motor run capacitor is hanging. This space is located under the limit switch that stops the humidifier when the water level is low. This piece of foam prevents the capacitor and the wires from hitting the outer wall. This helps a lot to reduce the humming. Previously, the humidifier would start humming much more strongly for no apparent reason. That was probably caused by the capacitor being just at the right place to resonate with the wall.

Overall, if you buy a Honeywell HCM-9006, these are the main modifications I would recommend to reduce the noise :

1. Prevent the capacitor and wires under the limit switch from touching the outer wall.
2. Balance the fan.
3. Add weight to the outer walls.

In the end, I am not sure if I would recommend this humidifier. Maybe if the manufacturer modified the design to eliminate the humming…