Wiring Aprilaire 500A to Armstrong Air Ultra V

[DoinItMyself]

I'm almost ready to tackle the installation of my Aprilaire humidifier, but I need some advice on powering the humidistat. The humidifier came with a 24v transformer, but I noticed that there already is a 24v transformer installed inside my furnace that is powering the thermostat. Is it a bad idea just to piggyback off the thermostat power terminals to power the humidistat?

The Aprilaire instructions specifically state that the humidistat power should not be tied to the blower motor's power... I'm assuming that doesn't mean I need to run a whole new feed from my electrical panel just to power the humidistat, correct? I'm assuming they don't want the humidistat power source to either turn on and off or vary in voltage?

Assuming I can piggyback on the thermostats power source, would it be safe to connect the humidistat's "R" to the furnace control panel's "R" and the "C" to the "C", respectively? That would sure make wiring easy.

Aprilaire 500A wiring schematic:

http://www.filtersusa.com/Aprilaire/install_500A.pdf

Wiring diagram and photos of the control board in my furnace:

Armstrong Air Ultra V Tech 91 Furnace album | Todd Taylor | Fotki.com

(Note that you can download the original photos via the link below the photos so the diagrams can be read.)

Thanks for your help!

[Jay11J]

The best way to wire this is use the trasnfromer that comes the humidifier.

You wire the transformer (Line voltage to HUM and Nutrural)

Low voltage side of that goes to Cf and C/G.

Then R and C from the furnace board to R and C at the humidistat.

[DoinItMyself]

Thanks for the reply, Jay.

Reading your post forced me to take a second look at the wiring diagram on the furnace. It's a good thing you pointed-out that the "HUM" connection on the furnace's control board is 120v.

Just to confirm, you stating that it's OK to tap the same "R" and "C" connections on the furnace's control board to power both the thermostat and humidistat? I spoke with an electrician and he thought it might be best to tap a new power source for the humidistat and leave the furnace control board alone. That, however, would require me to have 2 step-down transformers (one for the power and one for the HUM wire.)

[Jay11J]

Originally Posted by DoinItMyself

Just to confirm, you stating that it's OK to tap the same "R" and "C" connections on the furnace's control board to power both the thermostat and humidistat?

Yes, it's OK, the power use is very little to run the display on the humidistat.

I spoke with an electrician and he thought it might be best to tap a new power source for the humidistat and leave the furnace control board alone.

No need to worry about that. R and C as I said above takes very little power.

The W/G, and Cf is the one going to use a little bit more power since that powers up the water valve on the humidifier. and you have that on the transformer by itself.

[DoinItMyself]

Took me most of the weekend, but I got it in and working (or at least it seems like it is!)

The only real problem I had is that when I went to cut the hole for the bypass in the return vent, I didn't tighten the pivot point enough on the circle cutter tool I had and the hole ended-up being oddly shaped by the time I realized what was going on (hence the square patch in the photo).

Other than that, I'm pretty happy with how the project turned-out... especially when I powered it up and everything worked as planned. It figures that it's been raining here for the past day or so and a bit warm, so the relative humidity isn't too bad in the house. I'll have to wait until it gets colder before I can see if the humidifier actually solves the dryness problems I was hoping to solve.

For those of you who own a Dremel tool, I found using it with one of the new "quick connect" steel cutter discs to be a great way to cut the square opening for the humidifier. I cut a nearly perfect square and the edges weren't too sharp. I also used it to cut a 1 ft. piece of 6" duct... much nicer than using a tin snips.

[Jay11J]

Originally Posted by DoinItMyself

Took me most of the weekend, but I got it in and working (or at least it seems like it is!)

Glad to hear you are up and running. Looks good too!

It figures that it's been raining here for the past day or so and a bit warm, so the relative humidity isn't too bad in the house. I'll have to wait until it gets colder before I can see if the humidifier actually solves the dryness problems I was hoping to solve.

How warm was it your way? Right now, it's 3˚, and we got ice and some snow last night.

For those of you who own a Dremel tool, I found using it with one of the new "quick connect" steel cutter discs to be a great way to cut the square opening for the humidifier. I cut a nearly perfect square and the edges weren't too sharp. I also used it to cut a 1 ft. piece of 6" duct... much nicer than using a tin snips.

I'll have to keep that in mind.. I have a Dremel, but haven't really used it as much as I thought I would. I'll have to dig mine out again, and see if I have the quick connect steal cutter or not..??

I didn't see a full mode # is your furnace a two stage or not?

[DoinItMyself]

Originally Posted by Jay11J

Glad to hear you are up and running. Looks good too!

Thanks! I figure that even if it doesn't work like it was installed by a professional, it should at least look like it was! ;)

Originally Posted by Jay11J

How warm was it your way? Right now, it's 3˚, and we got ice and some snow last night.

We've got a balmy 6˚ this morning. On Saturday night, we got a LOT of rain which then froze solid on Sunday morning... so we got all sorts of humidity, but it's now frozen to my driveway :(

Originally Posted by Jay11J

I'll have to keep that in mind.. I have a Dremel, but haven't really used it as much as I thought I would. I'll have to dig mine out again, and see if I have the quick connect steal cutter or not..??

I guess the correct name is "EZ Lock". I bought a 5 disk starter set that included the "EZ Lock" mandrel for about $15.00. Considering that cutting metal seems to be the most common use for my Dremel, these new discs are much more user-friendly than the tiny standard discs that require replacing a tiny screw to get them attached.



EZ406 EZ Lock Starter Kit / Model: EZ406

Originally Posted by Jay11J

I didn't see a full mode # is your furnace a two stage or not?

I *think* it's a single stage? It's an Armstrong Air "91 Tech" running on LP gas:

91 Tech - Armstrong Air High Efficiency Gas Furnace

[Jay11J]

Originally Posted by DoinItMyself

Thanks! I figure that even if it doesn't work like it was installed by a professional, it should at least look like it was! ;)

I'd say you did better than some Pro may of done! The way the lighting was on the photo, almost looks like it could be used for an Ad for Aprilaire.

but it's now frozen to my driveway :(

Same here... Going to go out and try to clean it up before I head out of town, and before the mail lady comes.

I guess the correct name is "EZ Lock".

I know for sure I don't have that.. I"ll have to look for it when I return to work on Wed.

I *think* it's a single stage? It's an Armstrong Air "91 Tech" running on LP gas:

Yep, it's a single stage furnace.

What do you have for a thermostat on this?

[DoinItMyself]

Originally Posted by Jay11J

I'd say you did better than some Pro may of done! The way the lighting was on the photo, almost looks like it could be used for an Ad for Aprilaire.

My camera was having issues with the highly reflective surface of the steel. My basement is a bit too dark to not use a flash, but the bright reflection from the flash apparently messes-up the camera. :o

Originally Posted by Jay11J

What do you have for a thermostat on this?

Some el-cheapo Honeywell thermostat that came with the house. I can program the weekdays and weekends and that's about it. Would there be any reason to get anything *better*? There seems to be a million of them on the market... are there some whiz-bang features that I don't know about that I shouldn't be living without? :D I wouldn't mind having a built-in humidistat.

On a somewhat related note, do you have any experience with whole-house dehumidifiers? Wisconsin summers get really humid and our basement got really damp. However, our house stayed relatively cool almost all summer long... we only turned the A/C on a few times. I'm thinking that if I got a whole-home dehumidifier that not only would it help keep the basement dry for when I decide to finish the walls, it might nearly eliminate the need to use the A/C? I see Aprilaire makes a few whole house dehumidifiers. Do you have any experience with them?

[Jay11J]

Do you notice if your furnace turns on and of often?

Newer t-stat you can get the smart recovery, and if you are thinking of maybe getting a new one, any of the 7000 series t-stat would be fine. Or if you want a nice touch screen, i'd suggest the VisionPro, and they are really easy to program! heck, my own mother can program the VisionPro now herself, where the older basic model, she could not get it figured out, and was on HOLD.

A whole house dehumifier would be best if you did have the windows shut, otherwise, it's going to run all the time in mild summer that you may have the windows open. I would suggest the stand alone unit in the basement.