Nest wiring to Generalaire 1042 humidifier


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Old 01-08-20, 01:27 PM
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Nest wiring to Generalaire 1042 humidifier

Hi all, hope you'll bear with me and my amateur knowledge or lack thereof

I have a 3rd generation Nest thermostat that is successfully hooked up to my home furnace (which also has central air conditioning). I also have a Generalaire 1042 humidifier that is on the furnace, hooked up to an old manual humidistat via a solenoid. I'd like to connect things so that the Nest can control the Generalaire humidifier.

I've done a bit of reading here and elsewhere on the internet, but still just have a few questions--some to confirm my knowledge is correct, and some because I don't know the answer Hope you can help....

1. My understanding is that because the Generalaire 1042 doesn't have a transformer, no relay is required. Is that correct, or do I need to install a relay?

2. This may be an obvious question, but...what exactly should I buy in terms of the physical wire that will run from the Nest down through the wall to the lower floor and connect to the furnace and the solenoid? I know very little about physical wire other than what the term "gauge" refers to

3. Is this wiring diagram how I have to wire it (minus the HRV, which I don't have in my house)? https://www.doityourself.com/forum/a...7.41.57-pm.jpg

4. What equipment do I need to turn off at the breaker when doing this install, and at what point in the installation process? It's really cold here, so would prefer to be able to leave as much equipment running and heating for as long as possible while installing this.

Thanks all!!
 
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Old 01-08-20, 10:25 PM
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Welcome to the forums.

Maybe there is a spare wire in the existing thermostat cable ?
I will normally run a new larger cable. The actual wire size is #18 solid.
You can run a piece of two wire cable..... #18-2 thermostat cable.... and just use one wire.
You could run a single piece of #18 bell wire.

One wire from the solenoid goes to Common.
The other wire from the solenoid goes to the *.
 
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Old 01-09-20, 07:01 AM
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Thanks very much, appreciate the help!

I had thought about using 18/2 wire...but if the solenoid is down near the furnace and needs to be connected to its Common, and since the Nest is upstairs and needs to be connected to the solenoid, I probably need two completely separate wires because they'll be in two completely separate areas, right? i.e. both wires will connect at one end at the solenoid, but then one of them goes in one direction to the furnace wiring block a couple feet away, while the other one goes up into the ceiling to the second floor and up to the Nest's * connector, right?
 

Last edited by canadavenyc; 01-09-20 at 07:18 AM.
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Old 01-09-20, 08:09 PM
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The reason for using 18-2 thermostat cable even though you only need one wire is that the brown jacket protects the wiring inside. You can use a single wire from a two wire cable. You can also run single conductors.
 
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Old 01-09-20, 09:05 PM
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OK thanks--pardon my ignorance again, but is the need to protect the wire with the brown jacket simply because it's being dragged through walls and could snag or snap otherwise? I can see that for the wire going from the solenoid to the * on the Nest. For going from the solenoid to the furnace that sits next to it, I'm guessing I can just use a four-foot single wire (that's what you mean by "single conductor", right? Sorry...I'm not quite up to speed with the terminology).
 
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Old 01-10-20, 06:05 PM
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The jacket is for general protection...... from chafing.... heat.... abrasions.
Yes.... single conductor is just one solo wire.
 
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Old 01-10-20, 06:35 PM
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OK, got it, thank you

So I'll go get 18/2 wire, use just one of the two smaller wires inside the 18/2 wire to connect to the * slot on the Nest, connect the other end of that smaller wire to the solenoid once I've fished the 18/2 wire downstairs, then find a separate basic single-conductor 18-gauge wire to connect the other part of the solenoid to the furnace's C terminal a few feet away.

Will report back on how it goes
 
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Old 01-13-20, 07:42 AM
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Well, I decided to just bring in an HVAC person. There's other things going on--looks like whoever hooked up the furnace originally may have not set it up properly (it's a two-stage furnace but it looks like only the single stage wire is hooked up...?) Also the hole for the wiring for the Nest is extremely small...would be difficult for me to get the wire run. I'll just have a pro do it and save myself the hassle But thank you!
 
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Old 01-14-20, 08:55 PM
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OK, installer got everything hooked up.

On a side note, I'm not sure I understand how humidification is supposed to work. All day the humidifier has been running, including often with the furnace pouring out heat. Yet the humidity in the house is showing as 25%. Now, here in Edmonton, it's been extremely cold outside, to almost -35C. I keep being told "in those cold temperatures it's normal for humidity to be about 25-30%." I don't understand that though--what difference does it make what the temperature is outside and how dry it is outside? Inside, where I'm running the humidifier, it's room temperature. Given how much the humidifier is running, the humidity should be really high. I understand that you don't necessarily want humidity to be too high because of the possibility of condensation and mold growth, but we're nowhere close to that. How do I get the humidity to be at around 40%? I understand that may not be desirable, but I can't seem to get remotely close to that level even if it was advisable to do so.
 
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Old 01-17-20, 10:39 AM
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HVAC tech Nest/humidifier wiring incorrect?

So, an electrician from an HVAC company came to my house to wire my whole-home Generalaire 1042 humidifier properly to my Trane XV95 furnace, all of which is to be controlled by a Nest 3rd gen thermostat (I had asked about this in a separate thread on these forums, but eventually decided to just have the HVAC tech do it).

My understanding is that the humidifier's solenoid is supposed to be connected on one wire to the Nest's * terminal, while the other solenoid wire is supposed to go to the furnace's common wire C terminal. However, instead of going to C, the electrician apparently hooked it up to the furnace's Y terminal.

Is that how it's supposed to be connected? I want the Nest to be able to control the humidity to be around 35% in our house, no matter what the temperature is outside (right now it's -35C outside). However, even though the Nest is showing an icon saying it's trying to humidify, the humidity for the last couple of days is stuck at 25%. Does this mean the wiring isn't correct, and the Nest thinks it's controlling the humidifier but actually isn't?

I wasn't home when the install was happening, but my wife told me she asked the tech why he wasn't hooking the solenoid up to the C terminal and snipping the BK JUMPER on the furnace that it says to snip, and he said "oh that's one way to do it, but that's not how we prefer to do it." He didn't explain further.
 
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Old 01-17-20, 09:11 PM
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I combined the two threads.

You've got me completely lost with cutting the BK jumper. Typically that used to slow the blower down for de-humidifying the air when in A/C mode.

As discussed........ the solenoid gets connected to the * terminal on the nest and C on the control board.
You can only deliver so much humidity into the air. As the air gets colder outside and infiltrates the house..... your humidity level will go down. 40% humidity is pretty high in the winter especially at extreme cold outside temperatures.

 
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Old 01-24-20, 07:05 AM
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Just wanted to say thank you...I finally got around to screwing up the courage to switch the solenoid wire from the Y terminal where the electrician installed it to the C terminal (I couldn't find the breaker to control the furnace, and I didn't want to blow anything up or break the furnace during our recent very cold snap, so I just turned off the furnace disconnect electrical switch and hoped that was enough). Once the solenoid was on C rather than Y, everything worked (of course).

The only reason I can think of why the electrician from the HVAC company wired the solenoid to the Y terminal is that on the furnance terminal block, the letter labels for each terminal might look slightly offset if you look at them from a slight angle....and "B/C" is right next to "Y"....so maybe he thought he was wiring it to B/C?? I don't know. Anyway, it's working now, and just wanted to say thanks for all the help and advice.
 
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Old 01-24-20, 08:04 PM
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Good job. Thanks for letting us know how you made out.
 
 

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