rewiring humidifier control

[Nate Nagel]

Hi all,

I have an old Aprilaire powered humidifier connected to my furnace, which is an old Ruud 90+ gas unit. Currently the humidifier is enabled whenever the fan is running. I assume that there is a terminal on the board that goes hot when the fan runs, intended for this connection. Here's the issue - it's cold enough here and the insulation in my house is uneven enough, that currently I have the fan manually turned on low speed all the time to provide circulation. Otherwise my bedroom gets as cold as 62 degrees when the downstairs, where the thermostat is located, is 67 degrees. This allows the humidifier to operate when there is no heat call. What would be the best approach to change things around so that the humidifier operates only when the furnace is actually firing? I bet I could come up with something that works by looking at it myself, but I figured I'd throw this out there in case there were any "gotchas" that I might overlook.

thanks,

Nate

[Pete C.]

While you could simply reconnect it so that the burner firing enables it, I'd suggest connecting it to a humidistat, so that when the fan is running *and* the humidity is low it will run, and of course not run when the humidity is high.

[Nate Nagel]

It's already got the humidistat control, the problem is that it gets so dry indoors when it is cold out that it's calling for it to run near continuously. This means that when the fan is running but the furnace isn't firing, there's still water flowing through the humidifier which is likely mostly going down the drain rather than into the air. I'd rather fix it so that it only runs when the furnace is actually firing so most of the water gets into the air and then it shuts off when it goes back to the low speed circulation fan.

I suppose I could also move the humidifier feed over to the hot water line, but I don't know if that would still work well when the furnace isn't firing.

Nate

[Mikepier]

I have an Aprilaire hooked up to my furnace also, but it only comes on when heat calls, not when the fan is running by itself. I just checked the wiring on my furnace and the humidifier is hooked up to the W and C terminals on the circuit board, so you can check if thats correct on your furnace. You might have your humidifier wired up wrong and thats why it comes on even if you only have the fan running.

[Nate Nagel]

Follow up: I started looking at what I have closely, and the only "control" wiring from the humidifier is to the humidistat itself. So I figured that it must be controlled by cutting power to the receptacle that it's plugged into. Unplugged it, powered furnace back up, 120V at receptacle. Waited for heating cycle to finish. 0V at receptacle (which is mounted on the outside of the furnace) OK, so there's a relay inside there that is cutting the 120V to the humidifier to shut it off. Powered furnace back down again, opened up control box. I see that there is a "HUM" terminal but nothing is connected to it. There is a pair of black and white THHN entering the area the white is connected to neutral and the black is connected to "EAC." Not sure what that stands for - but I suspect that that is somehow controlling the humidifier because it's obviously field wiring (looped 14AWG rather than a stranded wire with a factory crimped end.) I can't see where it goes, but am I on the right track?

Main questions:

- What does "EAC" mean on a furnace control board?

- What are the typical voltages on the "HUM" and "EAC" terminals?

120VAC? 24VAC? 24VDC? I'd check 'em myself but it's kinda hard to keep my thumb on the pin switch, hold a multimeter, *AND* operate the thermostat upstairs :) I guess I'm wondering if that's just taking 120VAC direct to the recep or if there's a relay hidden somewhere in there that I need to dig deeper to find and verify. It's pretty hard to pull the cover on the recep box too, once it's warm I really need to relocate a lot of this stuff to make it more user friendly (one screw is partially blocked by a drain line, etc.)

thanks

nate

[Nate Nagel]

More info...

I took the humidifier apart to check it out... has its own internal

24VAC transformer, but the blower motor is 120VAC. Also, after much web searching, it appears that "EAC" is usually 120VAC and does in fact go hot when the blower is active, "HUM" is usually 24V and goes hot only when there is a heat call. I guess I still need to verify this with a meter on my particular furnace because neither the board nor the wiring diagram pasted on the inside cover explicitly states. Unfortunately Ruud's web site seems to be completely down otherwise I'd just look for install docs... (the "owner's manual" that the PO's left us is useless) I assume that "common" is a common neutral for everything 120 or 24?

Am I mostly correct so far?

So... it would seem that the easiest way to make this work is to ditch the wires coming from "EAC" and "COM" which presumably run straight to the recep for the humidifier, wire that recep always hot, then run a pair from "HUM" and "COM" to a 24VAC ice cube/PAM/whatever and intercept one of the legs from the humidistat? Actually I wouldn't even theoretically have to rewire the recep if I'm understanding this correctly, but I like to keep things clean and easily understandable so nobody looks at my work and goes "what the hell was he thinking?" Also that would make it neater if I were to have to replace the humidistat down the road because if I understand it correctly the newer electronic ones need a constant 24V (which I assume I could pick off of the xformer built into the humidifier) and like to be powered up all the time not just when the air handler is running.

Is there some handy online magic decoder ring for all the terminal designations for HVAC stuff, e.g. furnace control board, thermostat, and humidistat? I've DL'd all the manuals I can for equip. that I have but it seems that there is a basic assumption that one knows what all those letters stand for and while I'm relatively handy and (I'd like to think) intelligent, I don't have much (OK, any) experience with HVAC. What the heck does "EAC" mean, anyway? (I'm sure that I'll smack my forehead when someone tells me, but it's not coming to me right now.)

If you've read this so far, I greatly appreciate any insight :) Wow, I apologize for how long this has become... only explanation I can offer is when I start to get into a project, I really get into it until I understand exactly what I have to do.

nate

[hrhofmann]

de quoted text -

Since you have a voltmeter, you chould be able to poke around and find some point that is only energized when the gas valve is energized. That may be the primary of the transformer that feeds the gas vavle. If the thermostat and other controls are all on the 24V side of the trransformer, you are SOL unless you want to buy a transformer and wire it backwards to develop 120 V from some point in the 24V control circuit. Can't you throttle down the water flow slow not so much goes down the drain on a continual basis?

[Nate Nagel]

Forgot to mention, none of the above is really meant as a knock on the original installer of this setup. When we moved into the house the HVAC was heat only, no AC, and the thermostat was an old honeywell round mercury thing. So there was no possiblity of running the fan without the furnace being active. This whole situation is entirely caused by our desire to have AC and a fancy electronic thermostat with all these features... just trying to make it right, is all.

nate

[Mikepier]

My partucular model has no blower, it's mounted outside the return plenum and it's only the 24VAC that opertes it. I was not aware there are 120VAC models with blowers, so I have a totally different animal than you.

[Paul Franklin]

EAC == Electronic Air Cleaner

Paul F.

[ransley]

You are still evaporating water without heat on, just less. Do you have an accurate humidistat, analog need calibration every year. If you condense anywhere you have to much humidity, April air sells a system that tracks outside temp and automaticly keeps you set point, which you set at just under condensation. How much water per day does it use

[trader4]

That leaves me confused because previously you said the humidifier was plugged into a 120V outlet on the furnace. The Aprilaire's I'm familiar with that require 120V use powered fans and mount on the hot side. The bypass models do not use 120V and mount on the return.

I have an Aprilaire powered unit that is connected the way you want. When I installed it, I found 2 convenient 24V terminals that come on when the gas burner is on. You should be able to do the same thing.

But, on another note, I'm wondering how energy efficient your whole situation is. I would think constantly running the blower to even out temp differences presents two problems:

1 - The blower constantly running uses a considerable amount of electricity. 2 - Constantly moving room temp air through ducts has to result in some additional heat loss, which I would think could be considerable. For example, in my house the ducts run through the basement, some up outside walls, where due to the ducts vs wall size, mean those ducts have no insulation around them inside the walls, etc. Also, most duct systems are far from perfect with some air leakage, etc. The more air moved through there, the more loss.

I would suggest looking at:

balancing the system better by closing off some of the downstairs registers, particularly those that are on a duct run that also serves upstairs

consider getting booster fans, either the kind that sit at the registers and come on automatically with the heat, or the kind that you can insert into ducts and wire to the furnace blower or other AC

consider some small electric heaters upstairs to supplement the existing heat

[Nate Nagel]

D'oh! that makes sense. My "HUM" terminal must be 24V that would explain everything. I do have an air cleaner, but it was installed with the A/C and is not connected to the furnace control as it has its own control (differential pressure switch turns it on)

nate

[Nate Nagel]

Right, I was just kind of hoping that someone could point me in the right direction before I had to draft a helper to turn on/off the thermostat while I probe around in there.

Meh, not so much. I am only aware of one "hot" duct that runs up an outside wall. Most of the ductwork runs right up the center of the house. I agree, loss of any kind is bad, but I don't think there is a whole lot.

I have done this, although some of the dampers do not close all the way. I'm trying to get the design department to agree on a style/finish and replace all of the registers/return grilles throughout the house.

Not sure how this would help...? problem seems to be that the masonry walls of the 1st floor simply lose heat at a much slower rate than the wood framed walls upstairs. I ASSume that the eventual solution is to insulate the upstairs walls, but until I can afford to do that I'm just trying to keep it comfortable inside... Only really need to do this when it drops below about 25 degrees outside which is not that often.

nate

[Mikepier]

In my first post( 4th one down) I never metioned 120V on my unit. Are you referring to the OP?

[nicksanspam]

Airseal the house.

Nick

[trader4]

The aux blowers help by moving MORE hot air upstairs when the furnace does run. An additonal small electric heater in an upstairs bedroom could use less electric than running that big blower all night

Also, along the line of what Nick said, if the humidifier is constantly running, it suggests moisture is somehow escaping at a high rate. That could be due to a lack of vapor barrier or air leaks. With it constantly running and very cold, I'd be concerned about where that water is going and condensing.

=A0problem seems to be that the masonry

de quoted text -

[trader4]

Yes, sorry got the posts mixed up.

[Nate Nagel]

Well, after all that I got lucky. Drafted the girl to work the thermostat while I probed the connectors on the control board (oh, that sounds so dirty) here my furnace has a 120VAC "HUM" terminal so I moved one wire about an inch and now it works correctly. Didn't have to buy a relay or anything.

nate

[Tony Hwang]

Hi, Your humidistat will llow it to run only when humidity is needed as is. No need to change anything.