Whole house humidifier

So I have a honeywell whole house humidifier hooked up to my HVAC. I'd like to control it a bit better. I figure I would need a relay to be inline with power so that let's say RH is at 48% and the furnace comes on but the humidifier would not. But anything lower it would come on when the furnace kicks on until that set point was reached again. Not sure about how I would go about writing the rule nor what relay (shelley?) I should use. Maybe @aaiyar can chime in as he's pretty rad with HVAC stuff.

If I had to do this, I would use an original ecobee3 or ecobee4 thermostat, both of which can control a humidifier (or dehumidifier). The ecobee3 lite cannot.

If you're doing this with a relay, you can use one of these:

Works with Hubitat and the relay terminals can handle the 24VAC/1A that your humidifier is probably controlled by.

I'm 99% node-red for my automations, so I'm tagging @neonturbo and @dylan.c who are both really good with HVAC stuff and RM.


Yeah my humidifier is connected directly to the board in my unit. Wirinig diagram on last page https://www.acwholesalers.com/manuals/GMEC96Tech.pdf

I figured using a relay was my best bet.. Another option is I could simply use a smart plug to accomplish the same thing... The unit plugs into a 120v outlet. I could use that instead of the relay I think and just write a rule. (Again I'm not sure how to address the rule) It would still go off when the furnace turns off because of the terminals but would only have power if RH was at 48%. Does that make sense?

Your diagram shows the HVAC board supplying 120VAC to the humidifier. It shouldn't need both the wall plug and 120 from the control board. Can you confirm that both are indeed connected?

Also, does your humidifier have any control devices that are not connected to the HVAC unit? For example, mine has a separate humidity [garbage] and a pressure switch that indicates when the fan is running.

And lastly, what device tells your current humidifier to run or not, and are you planning to use the same device for the control scheme described above?

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Define "better".

My advice is that you are much better off using a dedicated humidistat if your thermostat isn't doing what you need it to. You need to look for a humidistat (or a better thermostat) that has outdoor temperature compensation. There is a fairly complex formula that compares inside humidity and outdoor temperature to calculate dewpoint, and keep your windows from sweating.

Here are a couple examples:


The humidifier has its on 24v relay that connects to the main board and is activated/deactivated by the furnace turning off or on. The primary power comes from 120v

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Yeah, a humidistat and a pressure switch in the cold air return

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Is this the relay? The coil voltage is likely 24VAC but the switched side appears to be 120VAC. Unless your unit is not connected to these terminals. In the end, if you don't modify this part, it really won't matter.

This is probably your easiest point of control. Put a relay (Zooz ZEN17 would be my go to option) in series with these and either crank the humidistat to the max or just bypass it. Option 2 is a smart plug ON the main power. The rest is just rules to control how/ when you turn it on.

Yes... something connected to HE that gives reliable humidity measurement.

That's one option. I use a forecast app and RM to adjust my humidity based on the lowest temperature in the 3 day forecast. This really depends on where you're located. I'm looking at -14 F on Saturday night. You might live somewhere warmer. I can share my rule if you'd rather go that route.

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I have this humidifier https://images.thdstatic.com/catalog/pdfImages/e2/e2af7dfa-f704-4954-9366-e117312abd8b.pdf

The relay is right on it. The two wires from there are connected to the common and a switched 24v terminal on the furnace board. (it uses a PCBBF139 CONTROL BOARD). 120v powers the motor and the relay. That's why I was thinking of a zigbee outlet instead of an additional relay. The zigbee outlet would only energize the humidifer when the furnace comes on when rh is below 48%... Does that make any sense or is my brain off?

That is the same humidifier that I have and the same way I currently control mine.

What color are these? As I mentioned earlier, it might not matter but I want to understand.

Also, you should hear a loud click every time the humidifier starts. That's not a relay, it's the solenoid valve for the water supply.

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Here is the link to how I have my rule set up. I use an ecobee for my humidity sensor...

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So now I feel dumb. I thought the humidifier was tied in to the control panel of the furnace. I discovered by running new thermostat wire today (to take advantage of the two stage heating they never set up right to begin with) that the humidifier is in fact NOT tied directly in. It's simply the pressure switch, that is activating the solenoid. So at this point it would be just the zigbee outlet needing to turn on when humidity is low turn on but turn off when the furnace turns off..

The pressure switch will take care of this part. The outlet can just be set to look at humidity only.


Humidifiers do no good if you can't run the furnace fan while it is on.


Well, that's the thing, the humidifier only comes on when the furnace comes on only if the RH is below 48 RH... As stated above it goes off when the furnace goes off. So the humidifier is never on when the furnace isn't and only on when the furnace is during a specific condition.

I have a Honeywell. Whole house steam humidifier. Flakey maint but works. The Iaq prestige Therm integrates with it and also has outdoor sensor. It will turn on the fan separate from the heat when needed. I have found at least in NH that you will never get above 40% in the winter unless you want to run 24x7 and have a huge bill. And not above 35% when outdoor temp is near 0 or below. So that turn on below 48% ... at least in our area would keep it on 24x7... if that is what you are trying to do... not good.

Being in western PA, winter humidity is in general pretty good. I'm not even running it right now and RH is about 52% at the moment. (Mine is a honeywell as well, see link above).

Ya not too cold yet in NH so haven't even turned ours in yet. Still between 35-40 % in house. Not to mention that we are in FL right now for 2 more weeks.

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I don't know if yours is the same as my steam one and I also have osmosis filters but the idiot that designed those plastic hose compression fittings should be drawn and quartered.

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This is the one I have

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