# How to install Aprilaire transformer?



## Studly (Feb 27, 2009)

I just bought an Aprilaire 58 digital humidistat (I believe this humidistat comes standard on Aprilaire humidifier models 600 and up) to install on my existing model 550 humidifier. I think I understand the instructions pretty well, except a couple things.

The instructions say it needs a constant power source. The humidistat runs on 24v, so it has a transformer. The instructions say:
"Wire the external 24 VAC transformer into a constant power source other than the heating, ventilating, air conditioning equipment (HVAC) blower circuit. The transformer can be powered off the 120 VAC line at the junction box before it enters the HVAC."​I'm no electrician, but I'm guessing that means I can just wire the transformer into the electrical box that has a switch to allow power to the furnace.

It doesn't say much more about the transformer than that. The transformer has two leads that go to the 120v power source, an odd angled screw (looks too thick to be for a ground wire and it's not colored green) and then on the other side, the terminals to run the 24 volts to the humidistat.

I'm planning to put this transformer in a metal box, near the switch to the furnace. However, what is the angled screw for on the transformer? Is this used to somehow mount the transformer in a metal electrical box? But if it was for that purpose, I don't know why they'd angle the screw. Or am I mistaken ... that this is the ground screw?

If anyone can advise if my wiring plan sounds good and what this mysterious angled screw is for, I'd appreciate it. Thanks for the help!!


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## biggles (Jan 1, 2008)

you can mount it inside the furnace compartment and catch the 115V coming in there from the same switch that powers the furnace off.that screw on the back of the TR is for mounting it into a utility plate then onto a 1900 box so the 115V is boxed and then just the 24V is exposed.


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## Studly (Feb 27, 2009)

Thanks for the help, biggles. I'm guessing you mean that if I mount it inside the furnace compartment that I don't need to bother with the metal box, correct? How do I mount the transformer in the furnace compartment ... is there a spot where I can use that angled screw on the transformer to mount it in the furnace?


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## chris75 (Aug 25, 2007)

Studly said:


> Thanks for the help, biggles. I'm guessing you mean that if I mount it inside the furnace compartment that I don't need to bother with the metal box, correct? How do I mount the transformer in the furnace compartment ... is there a spot where I can use that angled screw on the transformer to mount it in the furnace?


You have to use a box for the transformer. Just mount it to the disconnect switch box, I personally like the transformer switched with the furnace power. The angled screw is what holds the transformer to the box as well as bonds the transformer.


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## beenthere (Oct 11, 2008)

You knock out a knock out plug on the box.
The angled screw is used to hold the transformer on the box.


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## chris75 (Aug 25, 2007)

beenthere said:


> You knock out a knock out plug on the box.
> The angled screw is used to hold the transformer on the box.


 
So easy a caveman can do it. :thumbsup:


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## AndrewF (Dec 29, 2008)

Or, if your furnance has a 24 vac transformer already, you can tap off the C and R wires as a power source.

I did that instead as I dont have a 115 vac power source near my unit as it is all 220. It also took a lot less work than having to install and run separate wires for the aprilaire unit. Since I already had to run control wires from the humidistat into the furnace (air handler) it was a simple install.


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## biggles (Jan 1, 2008)

if you mount it on the horizontal or vertical inside the control section of the furnace you don't need any box.screw it down on the 2 foot mounts, wire the 115V to the incoming 115v from that utility toggle outside the furnace,and you good to go.outside you will probably have to add a 1900 box to an exsisting box with plate and knock out...because you won't have the room to side mount the TR to an exsisting box if that is screwed onto the side of the unit....that the reason for a plate cover with a knock out and that angled screw on the 115V side.


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## key1cc (Nov 21, 2008)

*If a picture is worth a thousand words, what's a video worth?*

Attached is a link that gives you access to a video instructing how to install an humidifier including the transformer. The site shows you a little 3 minute teaser video for free but you have to buy something to get the DVD. The DVD also shows you how to do a few other HVAC related installations. 

I got mine free when I purchased a Generalaire 5" filter media cabinet from them (with merv 10 filter for only $99 at the time...it may be a couple of bucks more now).. My point is you don't have to buy the video for $50 bucks since they sell most HVAC related items, you can buy something and get it free. 

http://www.alpinehomeair.com/view.cfm?objID=55762B49-9E5E-483A-9781-FE867F34FC44

Key1


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## princesnicole (Sep 18, 2009)

if you arise it on the accumbent or vertical central the ascendancy area of the boiler you don't charge any box.screw it down on the 2 bottom mounts, wire the 115V to the admission 115v from that account toggle alfresco the furnace,and you acceptable to go.outside you will apparently accept to add a 1900 box to an existing box with bowl and beating out...because you will not accept the allowance to ancillary arise the TR to an existing box if that is busted assimilate the ancillary of the unit....that the acumen for a bowl awning with a beating out and that angled spiral on the 115V side.

_________________
Aprilaire


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