# Humidifier wiring



## sgw1064 (Oct 28, 2010)

I have a humidifier with a rotating cage and float switch for water supply. 25 year old lennox. Nothing labeled. Can I use the white and red wire coming from house thermostat to control humidifier cage motor


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## paul52446m (Oct 28, 2010)

sgw1064 said:


> I have a humidifier with a rotating cage and float switch for water supply. 25 year old lennox. Nothing labeled. Can I use the white and red wire coming from house thermostat to control humidifier cage motor



I have been in the heating bus. for 40 years. If you are determined to wire it that way then go ahead. If you run too much amperage through the thermostat 
 you will burn it up. Most thermostats are made for max 1.2 amps, you might be running as much as 1/2 amp. right now, so how much amp draw is the other things you are adding. Then you have a transformer on the furnace that has a VA rating. To find out how much amperage you can run on a transformer, you take the VA rating and divide that by the voltage. 20Va divide 24volts is .8 so if you are already using 1/2 amp or .5 amp that only leaves you .3 amps left to run the rest of the things you want to add.  I hate to get to tech. here, but these are the facts.    Later Paul


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## sgw1064 (Oct 29, 2010)

Thanks paul i was just trying to find out if i could use existing 24V circuit to run humidifier motor. i decided to take your previous advice and tie into the blower circuit and add a transformer. works great and thanks again


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## ccpyue (Feb 1, 2011)

Hello paul52446m  -  My humidifier cannot give me humidity over 26%. Pls help. Detail:

I newly installed a Lennox furnace and a Honeywell HE225 Flow-Thru Humidifier. I have the furnace FAN switch to ON all the time. My house humidity is as low as 26% only, can never exceed this. I need at least 35% for my skin problem. Problem I found is:

Water only supplies to the humidifier to make wet air is when the furnace is heating. Once the the furnace stopped heating (the FAN is still ON), water to the humidifier also stopped. I tried to turn the Humidistat, it "click" at around 25; but even I turn it to 40 and higher %, still on water supply to the humidifier. Therefore, my house humidity it very low.

What is the problem that cause this? How to overcome the water supplies problem, so that even the furnace is not heating, water still can supply to the humidifier to make air wet?

Thank you.


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## paul52446m (Feb 1, 2011)

ccpyue said:


> Hello paul52446m  -  My humidifier cannot give me humidity over 26%. Pls help. Detail:
> 
> I newly installed a Lennox furnace and a Honeywell HE225 Flow-Thru Humidifier. I have the furnace FAN switch to ON all the time. My house humidity is as low as 26% only, can never exceed this. I need at least 35% for my skin problem. Problem I found is:
> 
> ...


 how is humidifier   wired into the furnace? If its wired to the HUM. post then it will only be powered when the furnace is heating. 
 Did you use a add on  transformer to power it? If you did ,just power that 
 transformer from 120 volt so it will be hot all the time, then you can control it by the humidistat. Later Paul


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## Josty (Jan 2, 2012)

I have my humidifier wired to the HUM terminals and am also having trouble getting the humidity level in the house where I want it.  Going to try moving it to the EAC terminals so the cage will spin whenever the fan is on (not just when the furnace is running) and then set the fan switch on the thermostat to "ON" for a couple of days and see it that helps.


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## paul52446m (Jan 2, 2012)

Josty said:


> I have my humidifier wired to the HUM terminals and am also having trouble getting the humidity level in the house where I want it.  Going to try moving it to the EAC terminals so the cage will spin whenever the fan is on (not just when the furnace is running) and then set the fan switch on the thermostat to "ON" for a couple of days and see it that helps.



That should do the job of letting it run through the hum. stat.  Paul


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## shake (Nov 7, 2012)

sorry for highjacking this thread but it's the most relevant one I can find that is still recent. I'll make it short.

I have a furnace from the 80's so no humidifier connector.

I have a newer, dc wall-plug transformer powered, humidifier. So it basically runs all the time because there's no control.

I only want it on when heat is on.

Can I not just simply buy a 24vAC relay switch, connect one end to the furnace to toggle the switch, then connect the other end between the dc supply and the humidifier motor?

I don't know much about hvac but to me this sounds like it would work.

Where do I connect wires from the furnace / thermostat to the relay switch? To me, white = heat and black = common seems like the proper choice, but I'm uncertain.

I guess I don't know some fundamentals like is white positive or does it go to ground, does that wire switch - or + from the stat I suppose.

Thanks!


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## Wuzzat? (Nov 7, 2012)

You can put the 120vac AC input to the humidifier transformer across the 120vac blower motor "heating" winding but you have to unplug it when air conditioning is selected 
because the blower motor acts like a transformer and there will be much more than 120v on this winding when the blower motor "cooling" speed is selected.

Another way to do it is with a sail switch in the duct.

You want an AND function: the humidifier comes on when 
the air is too dry
 AND
 the heat is selected.


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## shake (Nov 7, 2012)

Thank you. I'd rather not rig something up where the furnaces AC is literally connected to a two pronged ac to dc wallplug transformer like that one my humidifier uses. I think all I really need to do is put the relay between the power going to the humidifier motor. It seems like the simplest solution to me. I just don't want to drive that relay off the wrong wires, so I'm hoping do get that cleared up.


Thank you all the same 

And yes you are exactly accurate:
what is want is so the humidifier comes on when the air is too dry AND the heat is selected. 

I believe the setup should be, wall socket > wall ac to dc transformer > power wire from that to humidistat (old analog one) > line to relay switch > relay switch to humidifier motor. 

Heat controls whether this relay switch is on or off. When heat is on, switch closes, circuit to humidifier is complete. When heat is of, relay switch opens, circuit to humidifier is incomplete.


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## Wuzzat? (Nov 7, 2012)

A typical HVAC transformer supplies 40 VA, 1.7A at 24V, so your relay coil should probably pull a max current of 0.2A or so in order that it doesn't significantly load down the existing transformer.

When I added an Aprilaire 760 to my '82 furnace I was surprised to find that the humidifier solenoid valve was working on 17 vac, down from the nominal 24 vac.  I would have said that the humidifier's transformer was being overloaded but the thing has worked now for years.

When you get your system working, make voltage and current measurements so you have troubleshooting data for when you'll need it.


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