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Whole Home Humidifier

1320352173735008201water-droplet-hi.pngDry air is very unpleasant to be in for extended periods of time. Last winter I tried to rectify the problem by using a single ultrasonic humidifier. It seemed totally inadequate, so I purchased a second higher capacity unit. I quickly became annoyed at how tedious it was to fill the reservoirs. And neither really solved my problem well. This year, I decided to install a whole home humidifier system.

Installing a Humidifier is not an easy task, and required quite a bit of knowledge of different building systems. See below for all of the work that I did, what I learned, and a list of parts.

System Selection

The most common type of whole home humidifier is a bypass humidifier, where water trickles down a special mesh pad that heated air passes over. The humidifier unit itself is quite large and must be attached to a fairly large surface area of unobstructed flat ductwork, as well as have a return/supply bypass. Unfortunately I did not have the space on either side of my furnace (cold air return, or heated air supply) to place the bypass unit.

I did quite a bit of research to find some alternatives. I selected a steam humidifier; an AprilAire 800. The AprilAire 800 is a steam generating machine which placed on a wall/support close to the hot air supply of the furnace. A steam pipe is connected from the steam generator to the ductwork. The AprilAire 800 has a replaceable canister with electrodes in it.  The unit fills the canister with water and generates steam. Periodically, the system will flush the mineral rich water out to reduce mineral buildup in the canister.

A significant benefit to a steam system is that it doesn’t need the furnace to run heat at the same time it is humidifying, it only requires air circulation.

The unit has a capacity of 34.6 gallons a day, but my configuration will be at 23.3 gallons a day. Seems the maximum capacity of a bypass unit would be about 12 gallons a day. Ultrasonic units have a capacity closer to 3 gallons a day.


Looking at any HVAC system, the largest part is usually the furnace/blower which heats and moves the air.  The air conditioning coils, which cool air, are usually hidden within duct work following the furnace. It was important not to damage the AC evaporative coils when drilling a hole and inserting the steam pipe.

Vent Stack

In order to fit the steam generator into my closet, and avoid the furnace’s gas supply line, I had to adjust the placement of the exhaust stack. I have an 80% efficiency gas furnace which requires an exhaust stack made of type B vent.  Type B vent is essentially double walled metal duct. I tied into my building’s common exhaust stack on the second floor, so I have to deal with the stack coming up from the unit below me.  The unit below me also has an 80% efficiency furnace.

My first attempt was removing the long 6 foot 5.5″ diameter section, and re-routing it with new 45 degree elbows, and smaller vent sections.  After getting the parts, and starting assembly, I discovered two things:

  1. I did not calculate the section lengths correctly.
  2. Type B vent from Amerivent is painfully difficult to work with.

Instead of buying additional type B vent parts and correcting my calculation error, I decided to rig my own system up with parts from Home Depot. The most important part of this vent stack was that it was double walled. The exhaust from the system below me needed to stay hot so that it would rise and leave the building above the 3rd floor.  And the exterior of the vent needed to remain cool so not to have any risk of fire or burns. My solution was a 6″ to 4″ reducer collar on both ends of the 5.5″ section I was taking out, and a 4″ flexible dryer vent within a 6″ flexible dryer vent as the ductwork.


I installed a Nest thermostat several years ago. I knew it had the ability to operate a humidity supply system when I started on this new humidifier project of mine, however, connecting the Nest to the AprilAire 800 was not as simple as connecting a wire to both devices. The nest can only connect to one device directly. In my situation, it was the furnace/blower/AC system. The AprilAire 800 is turned on and off by completing a circuit. The solution was to add a “common” wire from my furnace to the Nest, and then connect a relay to the common line and the asterisk connection on the Nest.  Here is the wiring diagram:

Nest W-Powered Humidifier

After connecting all the wires, the Nest detected the change, and I went through the options of how the humidifier needs controlled.  I selected that when humidity is requested, the fan should also operate.

The guided setup was pretty slick. I was even able to select what time the humidifier should NOT operate, which is nice when combined with my ComEd hourly electric supply pricing; I only run the humidifier at night when electricity is generally cheaper. If only Nest had a way to integrate the ComEd hourly price API and set an electricity price threshold for the humidifier to operate.

Power Supply

The AprilAire 800 can operate at 120 or 240 volts AC and run at 11.5 or 15 amps. It’s shipped to accept the most efficient and common configuration; 240 volts at 11.5 amps. Lucky for me, my 200 amp load center is right behind where I wanted to put my AprilAire 800, there was plenty of empty positions in the panel, and there was already an easily accessible conduit used for a whole home surge protector to run the new circuit within.  Through the research I conducted, I found 14 AWG wire was plenty for my 4 foot run of cable. One odd thing to me was that I didn’t need a neutral wire. Apparently that is how the 240 volt system works. Instead of a hot and neutral, there are two hot lines, but on different phases.

Water Supply

Almost any humidifier system on the market accepts a 1/4″ connection, which can be installed without soldering copper pipe. I was able to run a poly pipe from my HVAC closet down through my neighbor’s closet, and then into the basement. I tapped into my neighbors humidifier supply line with a tee, so there was no need to pierce another section of pipe.

One important thing I learned is this: when using compression fittings (rather than quick connect), poly pipe should use plastic sleeves, and copper should use copper sleeves. If copper is used on a poly pipe, the copper cuts into the pipe instead of compresses/seals the pipe, leading to leaks and possible 100% disconnection. I ran into both problems attempting to install my line. It’s only after significant research that I found the problem. What is most concerning is that kits sold with poly pipe frequently include all brass fittings! It’s funny to read the reviews on Home Depot’s website where most are negative, and if people are not complaining about leaking or failures, they are suggesting buying the proper plastic sleeve to prevent leaks.

The brass sleeves that came with the copper tee also had to be changed out with plastic sleeves. It wasn’t the simplest task, as the brass sleeves were somewhat “built into” the tee. Some force had to be used to remove them.


My HVAC closet already had a simple PVC drain system in place for AC condensate.  I connected to that with a new tee and even added a P trap.  I feel like such an accomplished plumber. Protecting my floor was important, the PVC cleaner and cement would easily damage the wood floor.


Installed Pictures

  1. idontusenumbers
    January 23, 2018 at 11:07 PM

    I’m pretty confident that an evaporative humidifier would work with just circulation as well.

    My biggest concern with a steam humidifier would be what happens to the moisture if the air was already at maximum humidity. Where would it condense? Is it a total non-issue?

    • January 24, 2018 at 9:47 AM

      An evaporative/bypass humidifier would work without heat, but not as effectively. One of my good friend has a bypass humidifier, and his heat must be on for the humidifier to activate.

      The Nest only allows setting up to 60% humidity.

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