Two furnaces, one humidifier - wiring help.

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Old 12-18-20, 08:31 AM
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Two furnaces, one humidifier - wiring help.

I have a single Aprilaire 700 humidifier on return that is used by two Goodman furnaces. I need to know how to wire the Aprilaire 60 humidistat to both furnaces so that either one being on will turn on the humidifier.
The two brand new Goodman furnaces (replacements) were professionally installed but I opted to later replace the old humidifier that wasn't working and not hooked up as part of the install.
Now I could use some help as to the correct way to connect the inputs and outputs.
 
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Old 12-18-20, 11:36 PM
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Welcome to the forums.

Do these two furnaces share common ductwork ?
If they do..... they should both be coming on at the same time.
 
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Old 12-21-20, 09:35 AM
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They share the same return and they do not come on at the same time. One furnace/AC is for the up stairs and the other is for the main floor and basement. The unit for the main floor and basement are zoned, splitting the two floors. They turn on when the thermostats for each of the floors require more heat.
According to what I have seen and the installer tells me, this is common for larger houses.
 
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Old 12-21-20, 08:13 PM
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Typically the humidifier is mounted in the supply plenum and the bypass duct is connected to the return.
In your case the humidifier will need to be mounted in the common return and the bypass duct gets connected to which furnace ?

If I were to wire this I would use the 24v transformer that comes with the humidifier to power the solenoid and the A60 humidistat. Then I would use two 24v N.O. (normally open) relays to activate the A60. One relay is connected to each furnace. You could mount the relays near the humidistat. There would be a two wire cable to each furnace. Once you choose the relays I can give you a diagram.

Some relay choices.
Emerson 90-380 relay
Emerson 90-370 relay
Dual 24v relay package (pretty cool)
 
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Old 12-31-20, 07:09 PM
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Thanks for the help!
I if needed I would opt for the dual 24v relay package.
I am thinking that I may not need that as I have 2 Model 50 Current Sensing relays.
But I would be happy to shell out $13.98 for the 24v relays if needed.
Sorry for the slow response... Christmas, New Year and a daughter got married.
--Mark
 
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Old 12-31-20, 10:02 PM
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No problem.
I don't think two of the A50's relay is going to work. You would need to try it. I left a diagram below. Try one A50 first. When that one is working add on the second one. See if one at a time will energize the h'stat and then see if both together will work. The A50's clamp over one of the motor power wires. Typically use the white neutral wire even though I showed the black wire. You can loop the wire twice thru the A50 to increase the sensitivity.

 
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Old 01-02-21, 01:04 PM
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Thanks, I will give that a try, as directed.
 
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Old 01-04-21, 08:59 AM
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As you suspected, using the A50's didn't work. I was surprised to see that they showed 165K if impedance when the blower is running and infinite when it wasn't. I would have expected to see a closed sensing relay show near zero ohms?
Looks like I need the wiring diagram for using the relays you recommended.
 
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Old 01-04-21, 09:20 AM
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Your diagram doesn't use all of the connections in the wiring diagram supplied by Aprilaire. Are they not needed?
I wish that they gave more information about what these connections are supposed to provide.
I do have an outside temperature sensor connected to my Model 700.

Also including the wiring diagram for my furnace to be sure I am making all the right connections.

 
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Old 01-04-21, 11:36 AM
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I don't use any G connections. I don't want the humidistat to call for blower and humidity. I've found that humidifying cool/cold air is water wasteful with a bypass humidifier.

 
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Old 01-04-21, 01:31 PM
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My relays are supposed to arrive on Friday and I will try this out. Thanks for your patience.
 
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Old 01-11-21, 07:46 AM
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I was able to talk with an Aprilaire technician about this subject and he suggested that I hook up the humidifier to only the furnace that supplies heat for the basement and main floor. With the auto mode for the humidistat the fan would stay on to provide more humidity to the air even when more heat is not required. The humidity naturally rises to the higher floor.
After following this advise I found it be a good solution. The upper floor of my house, even thought it does not trigger the humidifier has been maintaining a humidity of 2% higher than the main level. The main level of the house has maintained a 2% higher humidity than the main level.
So short answer, I didn't need to drive my humidifier from both furnaces.
 
 

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