Wiring humidifier directly to furnace board


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Old 10-28-16, 10:06 PM
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Wiring humidifier directly to furnace board

Hello everyone,

I came across this old thread but wasn't able to reply due to its age.

http://www.doityourself.com/forum/hu...-question.html

I want to eliminate the transformer as described in that thread, but have a question on how to close the loop. My furnace board has a HUM connection that supplies 24VAC.

My board here:
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I follow all the other connections.
-Humidistat control H2 to Yellow1 on Humidifier.
-Yellow2 on Humidifier to Hum (24VAC) on furnace board

What do I do with Humidistat H1 that shows it's running to C on furnace control board? Is that C = Common? I have neutral terminals that I can use, but wanted to be sure before proceeding.

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Thank you for your time!
 
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Old 10-28-16, 10:42 PM
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I don't recommend using the G and Gf connections. The humidifier should only run when in heating mode to be most effective.

The C connection is available at the furnace in the same place the other thermostat wires are connected. C is not neutral..... it is 24vac common.
 
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Old 10-29-16, 10:29 AM
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So I connect the humidifier control panel to C (where thermostat connects) twice? The left portion of the humidifier control panel is already connected to R and C. The two H for output then goes to the same C and the Hum on furnace board?

I will try without the G/Gf connections as you suggest since I am using cold water.
 
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Old 10-29-16, 10:38 PM
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This is like what you're doing. Having some comp. trouble so I couldn't post it last night.

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Old 10-30-16, 01:15 PM
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Wow, that's more simple than I imagined it to be. Wiring in this fashion will only turn on the humidifier when there is a call for heat correct?

Thank you!
 
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Old 10-30-16, 08:41 PM
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How does the system work differently if I used the Hum terminal that provides 24VAC instead of the R?

I plan to use your wiring diagram, just wanted to understand.
 
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Old 10-31-16, 05:35 PM
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Yes.... power (24v) on the W wire is what activates the automatic humidistat to turn on.

The HUM only becomes lives on a call for heat. You could use it to power the solenoid but not the humidistat. Using the R for all power only requires one wire.

If you were NOT using an automatic humidistat.... then you would need the HUM connection.
 
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Old 11-01-16, 08:36 PM
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Thank you so much for your help. Everything is installed and wired up. It functions properly in the test mode. I'm glad I was able to install this without having to use the included transformer. One less part to break and the wiring was easier your way.

Thank you!
 
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Old 11-01-16, 10:09 PM
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You're very welcome. Good job!
 
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Old 11-14-16, 07:44 AM
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Hi all, new to the forum and didnt want to start a new thread since this one seems like it's exactly what I need. About to install an Aprilaire 400 to a Payne PG9M condensing furnace that I believe has the HUM option. If I am reading this correctly, I should wire up per post#4 without using the HUM option or the external transformer so that it only runs when it's heating for max efficiency. Ill post a new thread if thats preferred, but I think this is what I need to be doing. Thanks!
 
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Old 11-14-16, 09:47 AM
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You can use the furnace for power. I like to use the separate 24vac transformer to run the solenoid but it is not critical.

If you are using an automatic humidistat.... you don't need the HUM connection.
 
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Old 11-15-16, 08:17 AM
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Thanks Pete!

I would consider installing the 24 transformer if there were a benefit, otherwise I prefer to get out of the attic ASAP. Is this just a preference thing or is there some benefit to doing it that way?
 
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Old 11-15-16, 09:21 AM
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It's not always known if the air handler/furnace uses a 24vac 40watt transformer. The worst that can happen is the smaller transformer fails from too much current draw and gets replaced with a larger one.
 
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Old 11-16-16, 12:19 PM
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In my case, the PG9M specs indicate it has a 40va 24V transformer. If I understand correctly, 40va is the same as 40 watts, and I should be fine to run this entirely as you had posted with minimal wiring.
 
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Old 11-16-16, 12:52 PM
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Yes... you are all set. V x A = watts
 
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Old 11-16-16, 04:59 PM
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Thanks for being super awesome!
 
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Old 11-26-16, 05:33 PM
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Hey Pete or anyone who knows.

Should this be in manual or automatic mode on the humidistat? Got everything completed today, and I when I was testing the solenoid didn't open up until I flipped the switch to manual mode. Maybe I was too impatient in my testing, so I figured I would ask, I wanted to get out of the attic as I was pretty tired of being up there, It's crawl room only. I do have the remote sensor run to the outside.
 
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Old 11-29-16, 05:04 PM
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Just re-read my post. I meant I flipped the switch to blower activation mode from off to on. Tried again today, and it did not turn off when I flipped it back (while in test and with the heater running). I am guessing that the way I have it wired, it wouldn't really matter which way the switch was flipped anyway.
 
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Old 11-29-16, 08:17 PM
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When you make a switch change..... you must turn power off to the humidistat and then back on to register the new setting.
 
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Old 11-30-16, 07:23 AM
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Thanks for that info. I believe I did not power it off last night, I will have to test again.
 
 

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