I have an older (Aprilaire? Maybe mid-90’s?) humidifier attached to my HVAC system. It has a little dial mounted on the ductwork next to it that controls the humidity level. Has anybody ever upgraded an existing system like this to something… smarter? It currently has no outdoor temperature sensor, and in the cold winters, where days may swing from 40F down to 0 at night, it can result in lots of condensation on the windows when I do not make those manual adjustments.
I’m also interested on this…
Picture or model number of the dial or humidifier? We need to know what tech it uses to drive the humidifier. Bet it is simply a two wire device, in which case practically any switch type device would work, I think the Linear relays maybe being the least expensive/most appropriate (or the Aeons). There is a SmartApp for humidifier control. You’d need something that reliably measures humidity, not sure what’s best for that.
Sometimes these are REALLY simple, and just plug into 110, and you can simply crank down the humidity dial, and use an outlet switch to run it. Get one with energy reporting and you can see what it costs you to run too.
Just my thinking…
That is an interesting idea… I’ve already automated some other stuff with the aeotec energy monitor switches… And I have a house full of Wireless Tags sensors (temp / humidity)… I’ll definitely need to look at how the device is powered! That might be the easiest way! I’ll also try to check out the model numbers for more info when I get home.
To be precise, if the humidifier has “smarts” in the control like a shutdown process, then you don’t want to outlet control it. My newer Honeywell Tru-steam would not be controllable in this way, but thankfully ties to my thermostats humidity control that has smart limits.
Found the picture I took of the sticker on the unit several years ago:
It appears to be an Aprilaire 560… But I’m discouraged by the labelling… Says:
24V - 0.7A - 60 Hz
Makes it sound like it’s running off the HVAC 24V power delivery, and not a simple 110V mains current 
You can probably apply a plug-in transformer 20VA or more, plugged into a regular Zwave switch. Then turn it off when your glass temp approaches dewpoint.
Now I’m looking at outfitting the HVAC humidifier with one of these:
If I can wire it in, and figure out where to put the outdoor temperature sensor, it should do all I want!
But where is the fun in that? Don’t you want to see status and humidity in your SmartThings?
24V is still ok, you can use a Smart switch and the already existing transformer. Just replace the humidistat with the switch. I think these would work:
A little less reliable, but waaaaay more fun. In all seriousness, don’t do this if you are not comfortable, I’m full of ideas, but I’m not there to help/diagnose, or clean up any puddles. 
This is what I would do. Get a smart supported “dry contacts” relay. Hook the dry contacts “normally closed” in series with your old manual humidstat. Turn the humidstat to the lowest setting. You need 110v to operate the relay but I am pretty sure it’s near by since the humidifier is using 110v. Don’t worry about the 24vac. It’s for a solenoid that’s control by your old humidstat. By hooking it in series and using the normally close contacts if the relay failed in closed positon. You will still be able to use the old humidstat.
Edit: an Aeon micro is not going to work.
I would trust the WST to give you humidity reading just put it in your hvac venting where you current one is at. Then if you have some way to tap into the action of it running you could hook up a monoprice zwave open close sensor contact in line with that so it status would show opened/closed depending if it was running or not running.
This would then allow you to see with ST if it’s running and what the humidity is at. You could get more involved by not using it’s built in brains to turn the device on and off and use ST to do this based on humidity, this would then require a compatible relay to turn it on and off.
I have a few other projects I want to do with the open close sensor contact. I think it’s time I buy a few so I can do a few projects and do some write ups on them.
I have a tru steam and I highly recommend . If u have a newer thermastat like.prestige it can control it and check outdoor temp which.it does. The beauty of this is it can turn on the fan and humidify independent of the furnace being on. The other ones like you have really need to furnace to be on otherwise without heat it will not work well. Anyway if you still want to do this it is simple. As someone mentioned the transformer for these are 110 either plugged in or wired directly as someone said just put a Zwave switch between the transformer and the 110. No need to futz with the humidistat at all. Leave that on.Max… then whenever u turn the switch/transformer on the humidifier runs. Now find or write a smart app that monitors indoor humidity via a device and outdoor temp via a device or weather tile. And have it turn the switch on when needed. There are charts on the web that show when you would get window frost based on outside temp and indoor humidity. The smart app could override running when this would occur
If there is not already such.an app. I could write on.in a few hours if there is enough interest.
this is an old thread… just wondering if anything new has come out for aprilaire humidifiers? thx!
Hey Keven, I just installed a old AprilAire 700 power humidifier today at my house. I think tomorrow I am going to add A relay to make control the heat blower on call for humidity not only a call for heat. I found a smart app that will use one of my sensors but it doesn’t calculate the outside temperature.
I’m hoping someone has an app I can do that with to help lower the level automatically in colder temperatures with outside sensor or local weather app.
Let me know what kind of relay you find to work with this. Would it be inline between the furnace and the humidifier, or is your humidifier plugged in or powered directly some other way?
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To clarify my reason for this is … I have a pellet stove that is thermostatically controlled
that does a lot of the heating load for the home. This keeps my central HVAC unit from running very often which would keep my humidifier from keeping up.
I am planning to use a simple fan relay to on the low voltage wire to the blower motor that is controlled by the humidistat.
Single pole double throw 24v. relay
So when the humidistat sees low humidity it energizes the relay, closing the points on the G wire from thermostat.
If this works the way I believe it will and I find a smart app to see inside multi sensor and compare to weather app for outside humidity. Then I can replace the humidistat with this smart relay
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I am getting an Aprilaire 600 with the digital display. It is connected to the Thermostat to turn it on and off. But my old one is connected with a sail switch and a humidistat . I guess I could wire the sail switch into a relay or something.
Hey Steve, I am planning to install Aprilaire 500M with a manual humidistat control (actually, I will not use its humidistat at all)
I will be wiring the relay with humidifier’s solenoid ( I will be using Dan’s [RELEASE] ST_Anything v2.9 - Arduino/ESP8266/ESP32 to ST via ThingShield, Ethernet, or WiFi based relay) and get the humidity data off my Honeywell T-stat.
You can use NEST Weather from NST Automations (https://github.com/tonesto7/nest-manager/blob/master/)
Here is an another app what I found here - https://github.com/greffinthenerd/automatic-humidifier
Thanks Alex, I will look all this over when I get home!