Installing bypass humidifier with nest

Hi there everyone,

I've stumbled on this forum, much like many other people before me, trying to replace an existing bypass humidifier with a new one. At the same time, I'm also trying to replace the old thermostat, and humidistat with just a single nest that will be able to control both. I'm a little bit confused as to how to hook up the various wires because the nest pro installation doesn't make mention of how to deal with this.



Currently, I had a Wait/Skuttle 900 bypass humidifier and downstairs it is attached to a device that you adjust for the relative humidity of the air coming in (sorry, don't know the technical term). and attached to the back of the humidistat



Coming out of this mechanism is two pairs of wires, one seems to go to the solenoid to run the motor that turns the drum on the humidifier, while another pair of wires goes to a power source.



Somehow, when I get upstairs, behind the humidistat control box, I also have two wires that were coming out of the wall



I have a dessert spring rotary disc humidifier that I'm looking to install as it doesn't use a sponge material which will inevitably become solid as a result of the very hard water that we have here. Based on the wiring diagram provided in the installation instructions it seems like the wiring is more or less what the current setup already has.



My questions are:

1) How would I hook up a nest with this type of humidifier that I want to install

2) Where would one recommend looking for the initial spot of where those mystery two wires came from at the humidistat upstairs.

3) Is there a humidifier that works better for my situation, and would have low maintenance in a hard water environment (I know PJMAX is a big fan of the Aprilaire units.)



Thanks for your help guys.

 

Welcome to the forums.

I have hard water which makes me a fan of the Aprilaire units where the evaporation media is flushed during operation. There are others that use this same format but I've found the Aprilaires easier to wire and maintain.

Most humidifiers have a pair of wires hanging out that need 24vac on them to operate the solenoid and in some cases.... an internal fan. The wiring is very straightforward.... one wire goes to the C terminal at the furnace and the other to the * terminal on the nest. There is nothing else in the wiring.... no humidistat or transformer.

I don't know why you have two humidistats. Maybe only one was actually active or maybe they were both connected and both needed to call for humidity.

 

Hi Pete,

Thanks for the quick reply, I'll try and find the source of those mystery second pair of wires hanging out upstairs and why they're there. One wrinkle to that is that my current furnace is quite a bit of an older model (it came with the house) when I go to look at the control board, it looks like there are only two wires coming out of it that go to the thermostat upstairs.





In this case, would I run the pair of the wires similar to the setup mentioned above with a transformer providing power to the humidifier, and of those two wires from the transformer, one would go to the C terminal on the nest to provide power, with the other return wire going to the * terminal on the nest? or would I need a relay somewhere in the middle to make it so that there is only a single wire going to the nest in the * tab. I know some people have said that the Nest itself can draw enough power to operate without having a common wire, but as I currently have the ability to pull some wires through hopefully, what would be the best manner in which to wire the nests.

Thanks again for your help.

 

That's a pretty old furnace.

You could try posting the model number which can be found on an ID tag on the sidewall near the burner.
See if there is wiring diagram on the blower door you can post for me.

We need to find you a C connection out of that furnace. The nest will need it and so will the the humidifier.

 

The furnace is a Lennox G8-110-5

I couldn't seem to find any wiring diagrams, except for on the blower motor which I suspect will not be helpful for you.



I have taken pictures of the current wiring setup in the furnace.

 

So I don't know if this would be of any help to you Pete, but it appears that the second Humidistat that was upstairs did not really do anything, as I was just tinkering around with the one down here and it can control the humidifier independent of the humidstat upstairs (I've verified this by taking out the humidistat and not having the two wires connected and it seems to run fine.

Now would it work if I ran a pair of the wires from the transformer with one wire going directly to the humidifier that controls the solenoid, with the second wire creating a loop between the Nest and the Humidifier? If so would I plug one wire into the C terminal and one into the * terminal?

 

Ahhhh... a Canadian model. That furnace is well over 30 years old so be sure you have the heat exchanger cleaned and inspected. With that age the heat exchanger is prone to rust-thru allowing CO into the heated air stream.

In post 3.... bottom picture.... is the wiring area. Can you take a picture with that cover off ?
In order to run a nest and humidifier..... the wiring is very important. Right now you have two wire connected to the thermostat. With a nest..... we'll need to identify and label the R, W and C wiring.



Some info... no wiring... Technical/000234.pdf

 

Thanks for the concern, I get our local natural gas company to come out and do a check of the furnace for me, and so far they haven't made any mention of the Carbon monoxide going into the heated area, I think they stick some probe into an opening they've made there.

So I took a couple pictures, not sure which one will be more useful.



The two blue wires appear to go to the blower motor, while the black and white wires go to the thermostat. On that control panel (if you'd call it that, under the black and white wire terminals it says Thermo, while under the blue wire terminals, it says 24V.

Let me know what other information would be helpful

Thanks again for all your help.

 

Does it help if I can run a new 5 pack thermostat wire up to the thermostat from the furnace room/area?

 

I need to see how your thermostat wire connects to the furnace. I don't see it in any of the pictures. I'm guessing it may be inside this junction box. Take a picture of the wiring inside this junction box and one a closeup so I can see what it says on those two modules in this picture.

 

Hi Peter, sorry for the delay and not providing the proper pictures to aid in your deciphering of my dilemma. Hopefully this will be more helpful.

The thermostat currently upstairs is just a very basic unit





It appears that the two wires that are connect to the thermostat are only the W and the R wires



These two wires arrive at the furnace and go to what I would assume be the control board where the two terminals that it's connected to say "Thermo" On the other two terminals it says 24V and it connects to a junction box (I believe that's the term)



This is what the front of the junction box looks like and it goes into another area beside where there's a bit of a mess of wires where it then appears to connect to the power that flows to the blower motor.



Hopefully that is a little bit more helpful for your purposes, let me know if there's anything else that I should actually be providing to you other than what I've sent over thus far.



Thanks,

Kelvin

 

The similar black looking junction box that has the red wires appears to have been disconnected from the system, and might have been used in the past to serve a similar purpose as to the one with the blue set of wires.

 

Thanks for the additional info. Still looking into this.

 

Is it possible to supply power to the nest using a transformer as I have two spare low voltage wires kicking around from what appeared to be from a previous humidistat.

Could I then run a relay to combine the two wires that are necessary to control the new humidifier into a single wire into the * terminal of the nest?