Changing old manual dial humidifier setting to something smarter?

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 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 app. I could write 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

smart control with dry contacts for low voltage

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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 (

Here is an another app what I found here -

Thanks Alex, I will look all this over when I get home!

What solution did you end up with? I have a furnace mounted drip humidifier thti’d like to adjust the % of humidity in the whole house automatically as our temps outside can swing 30c in a day and the windows build condensation from that. You’d think someone would have made a smart controller by now.

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I would love to hear what others have done too…I’ve been wanting to do this for years and I finally have most of the pieces available…just need to figure out how to control the humidistat.

Why not have it wide open and put some type of smart switch or relay on the power and then a humidity sensor to control on/off…

I do not have a humidifier hooked to my furnaces but I do have 3 humidifiers that I control with Smart Plugs which work out great.

I use webCoRE for my rules.

Thanks for your response. It seems like it should be so easy, but I got a little turned around when I looked at all the options for the switches/relays. Do you have a recommendation?

Depends on what you have. I have regular plug in humidifies and I use Iris Plugs and Peanut Plugs for on/off. I love the Iris Plugs because they tell me how much power I am using. Surprisingly, the humidifiers are pulling around 300 watts when running.

As far as humidity sensors, I would recommend the Zooz 4-in-1s sold by @TheSmartestHouse . They are pretty slick and the newer version’s batteries last longer and the motion sensors are faster.

I also use the super cheap Xaomi Temp/Humidity Sensors (the round ones) but they can be tough to pair and sometimes fall off the network…

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Here is my plan.


The Nutone relay will be in a new plastic gangbox drawing 120VAC from a nearby always hot plug. Two strand bell wire will go from the furnace Humidifier 24VAC power tap, through the Nutone relay, then to the solenoid for the humidifier. This allows the the Nutone relay to replace to rotary control.

I will mimic the knob settings in WebCore based on temperature ranges. If I get creative, maybe I’ll create an equation instead. I will compare the Centralite humidity level to the the desired amount based on the outside temperature. If humidity is too low, I will turn on the relay. If too high, I will turn it off. As I learn with the system, I will adjust the target levels to get the results I want. As long as the Centralite unit is consistent, it can be tuned in.

In theory, easy peasy lemon squeezy.

Did you ever get this up and running? If so, would you mind taking a few pictures of your setup, or perhaps a diagram for how you wired the contact relay?

You can find it here: Smart Furnace Humidifier Control. I have tweaked the Webcore to work a bit better and killed the notifications as I now know that it works.

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thanks for the link a lot. i shall start learning how it works myself too. may i ask questions if would have some? thanks

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