# Connecting humidifier to your furnace



## python01 (Mar 3, 2010)

Where humidifier should be connected to turn on only when the furnace is on?
I think I have seen somwhere that it can be connected to the blower motor via relay, not sure if it means that I would actually cut the cable and connect relay coil in series?
Is there a way to connect it without cutting wires?
I have trane xr90 furnace and flow through humidifier.


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## travelover (Mar 3, 2010)

On my furnace, there was a place to plug in a humidifier on the conduit board. Have you looked there? Other wise, just wire it so it runs with the blower, if you have a single speed blower.


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## python01 (Mar 3, 2010)

travelover said:


> On my furnace, there was a place to plug in a humidifier on the conduit board. Have you looked there? Other wise, just wire it so it runs with the blower, if you have a single speed blower.



I have variable speed blower so I probably can not wire it there. What the markings would be on connector board for humidifier?


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## kok328 (Mar 3, 2010)

If you connect to the blower motor circuit, you'll be running the humidifier when the A/C is on this summer.  However, you could always run the wires back to the thermostat control board in the furnace.


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## Wuzzat? (Mar 3, 2010)

You may be able to use a sail switch, which is a small sail mounted in the duct that actuates a Microswitch that controls the humidifier.


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## python01 (Mar 3, 2010)

Can I get them at most home improvement stores?
What would be proper name for this type of switch?


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## python01 (Mar 3, 2010)

kok328,
I  would like to run them to thermostat control board but don't know which terminals to use on that board and whether I should be using relay and how to connect that relay (series or parallel)


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## kok328 (Mar 3, 2010)

To activate the water solenoid from the tstat control board, connect the hot from the solenoid to the W (white) terminal on the tstat board.  Now when the heat & only heat comes on, so will the water for the humidifier.
If you are installing a humidifier kit, it should come with a humidifier controller to adjust the amount of humidity.  If this is the case, the wiring will be somewhat different.


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## python01 (Mar 3, 2010)

kok328 said:


> To activate the water solenoid from the tstat control board, connect the hot from the solenoid to the W (white) terminal on the tstat board.  Now when the heat & only heat comes on, so will the water for the humidifier.
> If you are installing a humidifier kit, it should come with a humidifier controller to adjust the amount of humidity.  If this is the case, the wiring will be somewhat different.



Yes I have to install it with humidifier controller so I would have to disrupt power to solenoid when furnace is not on and let it go on when furnace is on.
Should I connect relay coil between white and common ( I think it is marked C on the board and then use relay contacts to control the solenoid?


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## Wuzzat? (Mar 3, 2010)

python01 said:


> Can I get them at most home improvement stores?
> *Probably not.  Try HVAC supply houses in your area.  If you sound business-like they might sell it to you for the wholesale price.
> *
> 
> What would be proper name for this type of switch?



Honeywell S688A1007 Sail Switch with 5 in. Wide Sail
or you can make your own with a $2 Microswitch from Hosfelt.com or Radio Shack.

If you use this switch to control the 24vac instead of the 120v, the danger level of this project is about the same as having a meteorite hit the ground 10' in front of you.

I used homebrew logic circuitry to do this function, but my circuit must be unplugged if the AC is turned on because that puts ~2x the rated voltage into my circuit through the blower motor.  
It's not widely known but it is hinted at in the humidifier installation instructions, that when you put 120v into one winding of your blower motor to select the speed, the other windings are putting out all different voltages, some of which are quite a bit higher than 120v.  This motor acts like a transformer with multiple taps on the windings.


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## kok328 (Mar 3, 2010)

python01 said:


> Yes I have to install it with humidifier controller so I would have to disrupt power to solenoid when furnace is not on and let it go on when furnace is on.
> Should I connect relay coil between white and common ( I think it is marked C on the board and then use relay contacts to control the solenoid?



No.  If you do that, then you will be forced to use the humidifier to complete the circuit to enable heat.  As I mentioned, with a humidifier controller, the wiring will be somewhat different.  In this case you'll want to power the controller with the R terminal (Red) and the C terminal (Common).  Now you will enable to option to humidify or not when the heat is on via the controller.


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## python01 (Mar 4, 2010)

kok328 said:


> No.  If you do that, then you will be forced to use the humidifier to complete the circuit to enable heat.  As I mentioned, with a humidifier controller, the wiring will be somewhat different.  In this case you'll want to power the controller with the R terminal (Red) and the C terminal (Common).  Now you will enable to option to humidify or not when the heat is on via the controller.



When you say "power the controller" do you mean that I would use the R and C terminals to supply 24AC power to the controller instead of  using 110VAC - 24VAC transformer? If it is the case wouldn't my humidity controller go off when heat is not on?
Or do I connect relay solenoid between R and C and let the relay contacts complete the water valve circuit?

Sorry for asking so many questions but this is the way I would like to go and I have no experience hooking up stuff in the HVAC area.


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## kok328 (Mar 4, 2010)

When you say "power the controller" do you mean that I would use the R and C terminals to supply 24AC power to the controller instead of using 110VAC - 24VAC transformer?
*Yes.*
If it is the case wouldn't my humidity controller go off when heat is not on?
*No.*
Or do I connect relay solenoid between R and C and let the relay contacts complete the water valve circuit?
*Yes.*


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## python01 (Mar 4, 2010)

Thanks for all your help guys, will try to get it working today.


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