During the last cold snap, my wife and I were waking-up with sore throats nearly every morning, along with dry skin, static 'shocks', and a constant feeling of being cold even when the heat was set relatively high. Most of these are symptoms of overly dry air, so I started research humidifiers for our home. The previous owner had a relatively large, portable unit sitting in the kitchen. However, I didn't want to go that route for several reason:
- You have to constantly fill the tanks unless you pipe a water feed into the unit.
- You have to constantly adjust the humidity level manually which can be a science in itself (based on outdoor and indoor air temperatures).
- A portable unit won't humidify the air in the whole house.
- The larger portables can be quite a drain on the electric bill.
- Having a big, brown, plastic box sitting in the house is not very attractive!
I decided that a whole-house humidifier was the answer for me. Of course, that opened-up a whole world of things I didn't know. For instance, there are several types of whole house humidifiers: by-pass, steam, and forced air (and maybe more.) Of the 3, the by-pass system is the most common, relatively easy to install, and uses very little power. By "by-pass", it means that air travels from the return ducts, through the humidifier, and then through the supply ducts. Basically, the furnace does all the work as the water in the humidifier is evaporated into the air.
Once I decided on a whole home humidifier, the next issue was choosing a brand. Most big-box retailers seem to carry a Honeywell system and you can purchase an installation kit for an additional $75. However, the Honeywell system, like most other systems online, require you to manually adjust the humidistat as the weather and relative humidity changes in your house. That sounds like a pain-in-the-butt to me, so I opted for the Aprilaire 500A unit from FiltersUSA.com.

Pretty much the only difference between the Aprilaire unit and most other by-pass models is the control unit. It can read the outdoor temperature and use that to make decisions on how to control the humidity in your home.
Thanks to the forum moderator "Jay" on the DoItYourself.com forums and a rather details blog post, "How to install a whole house humidifier in 10 steps", I pretty much new what to expect with this project and what parts to by.
For the most part, the installation was pretty trouble-free, with one exception. When I cut the whole for the 6" pipe in the return duct, the center pin on the circle cutting tool I bought started moving and resulted in a whole shaped more like a "9" than a circle. As a result, I had to put a square patch over the whole and try again.
Rather than use a tin snips for cutting the whole for the humidifier in the supply duct, I used a steel cutting disc with my Dremel tool and that worked great. The edges weren't sharp and the whole was the perfect size when I got done.
Finding wiring to complete the project was kind of a pain and I just opted for a 50' section of 18 gage / 2 wire thermostat wire. I used it for everything, including the outside temperature sensor (which I mounted inside the intake PVC piping for my furnace near where it comes into the house.) Seems that this was the smallest gage wire I could get w/o going into 24 gage data cable.
One challenge I had was wiring the humidistat. My Armstrong Air furnace has a control board on it and not being an electrician, I had no idea how to make sure the humidistat stayed on at all times but knew when to humidify the air, and I didn't want to screw-up any of the voltages and blow something up. After asking a lot of questions, I found that I should wire the 120/24v step-down transformer that came with the humidifier to the connection marked "HUM" on my furnace. This is apparently a 120v switch that only has power when the furnace is kicking in, which is exactly what the humidistat needs (but at 24 volts).
To get the 24 volts of constant power for the humidistat, I noticed that there was already a step-down transformer powering the thermostat. I opted to just piggyback on the "R" and "C" connections for the thermostat, hoping that neither the thermostat nor the humidistat drew too much power to be an issue. After firing everything up, it all seems to work just fine. The transformer I installed in in the lower left-hand corner, and the 120 volt wires from it are coming-out from behind the panel at the upper-left (black and white wires... white to the "Common" pin, black to the "HUM" pin).
If I find myself with some more time, I'll post some more detail installation photos. But for now, he's the final product:
