Author Topic: Installing basic humidifier in a Rheem with standard thermostat  (Read 1424 times)

Offline Porcupinepuffer

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How many of you guys have installed a humidifier and humidistat on a Rheem with a non-communicating thermostat?

I installed one a week ago with an older tech who just showed me a quick and basic way of installing it by having the humidifier transformer power up from the EAC connection.

When I go through the manual " Rheem Furnace 92-24161-124-03 " it has a somewhat overly complex wiring scenario that seems to involve using an additional relay along with the humidifier transformer (apparently the furnace transformer is too tiny and weak to also power a humidifier), and essentially running 3 wires outside of the furnace cabinet just for the humidifier.

I have pretty much got it understood to the best of my knowledge, but it seems like a lot of connections and wiring for such a simple add-on. It seems the way it's shown in the manual is the best way to have the humidifier only work in heating mode and with the blower running, but it does seem like a lot of work.

I'm used to simply hooking up a common and a hum terminal on a carrier and calling it a day.

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Re: Installing basic humidifier in a Rheem with standard thermostat
« Reply #1 on: June 09, 2018, 06:34:18 PM »
I have never had a problem using the furnace's transformer to run a bypass humidifier.  With the R96VA furnace I would jumper the R and HUM STAT terminals on the control board.  Then install a jumper wire from R or HUM STAT to one of the HUM terminals.  When there is a call for heat and the fan is energized the HUM dry contacts will close.  Wire the humidistat in series with the solenoid and the 2nd HUM terminal and back to the C terminal.

The manual wants you to install the humidistat in series with the R and HUM STAT terminals, then a jumper from HUM STAT to the HUM terminal.  When the HUM dry contacts close it will power a field installed SPST relay.  They want you to use a separate transformer to power the relay and humidifier solenoid.  I agree this seems like overkill.

Offline walker

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Re: Installing basic humidifier in a Rheem with standard thermostat
« Reply #2 on: June 10, 2018, 06:34:17 AM »
is this the board with the humidifier dry contacts?

if so

there is many ways of doing it.

first wire a jumper between w and hum on the terminal strip. this will arm the dry contacts whenever in heat mode.

this is assuming a 24v humidiifier with a humidistat run in series, run one wire from the humidifier to one side of the dry contacts, run the other side to the c terminal, then run a wire from r to the other dry contact.

I can draw up a diagram if you need.

Offline Porcupinepuffer

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Re: Installing basic humidifier in a Rheem with standard thermostat
« Reply #3 on: June 10, 2018, 08:19:34 AM »
 Thanks guys. The company I work for is wanting the transformer installed, so with the additional information provided, I've drawn out a diagram that I believe will work while keeping only a 2 wire running to the humidifier/solenoid. I like the idea of powering the hum stat contacts by using the W terminal. Although I'm to the understanding that even with a jumper from R to hum stat, the IFC is still supposed to only engage the onboard hum relay contacts when there is a call on the heat speed blower. So I'm thinking either R or W jumpered to the hum stat should still achieve the same result.

Since I'm going to be using the transformer that comes with the humidifier, I believe I can install this without the use of an additional relay. If I go by figure 47/48, they basically show me needing a relay.

But if I go by figure 46, they show not needing a relay and 120v can be used on the hum terminals to the humidifier transformer... I know figure 46 is a diagram without a humidistat, but I believe i can easily wire it like figure 46 and use the 120v hum terminals as the neutral break on the transformer to turn it off/on only when a heat speed blower is present.

I just want to be sure the two hum contacts are basically you're common and n/o of a relay and wouldn't normally have any connection in any position to the board. I wouldn't want to backfeed 120v to the board where it only wants to see 24v.

I don't know if would trust the tiny onboard relay to be switching power on/off on a transformer. I know they usually give a nice little spark of in-rush current when they're switched on/off. Maybe I'll just install a relay to play it safe and know I can't fry anything.

Offline walker

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Re: Installing basic humidifier in a Rheem with standard thermostat
« Reply #4 on: June 10, 2018, 08:26:25 AM »
Of you want to use a transformer then of more the wiring from R and C to the dry contacts.  Keep the w to hum jumper.  Wire the transformer from L1 to Neutral, there is an an extra L1 on those boards.  On the low side of the transformer wire one leg from the humidifier to one of the dry contacts, then wire one side of the transformer to other dry contact and then wire nut the other side of the transformer to the other side of the humidifier, I can draw a picture of you don't understand what I'm trying to say.

Offline Porcupinepuffer

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Re: Installing basic humidifier in a Rheem with standard thermostat
« Reply #5 on: June 10, 2018, 11:12:33 AM »
If you don't mind making a drawing, that would be cool. I'm good with schematics, but I hate rheem's drawings and hate seeing contacts on a board without a real drawing to show exactly how the onboard relay is setup.

Offline Sergroum

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Re: Installing basic humidifier in a Rheem with standard thermostat
« Reply #6 on: June 11, 2018, 02:56:48 PM »
Would someone be able to explain to me the negatives of simply running a wire from W terminal through the humidistat relay then to the humidifier itself, and then back to common?  I understand that it would overheat the anticipator on the old thermostats, but any digital ones should be fine. Am I missing something?

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Re: Installing basic humidifier in a Rheem with standard thermostat
« Reply #7 on: June 11, 2018, 04:23:59 PM »
That would work with a single stage thermostat if the furnace was set to auto staging.  The problem is if you use a 2 stage thermostat with the furnace set to 2 stage, the humidifier would only run when W1 was energized, but when W2 was energized the humidifier would not work.  Essentially the humidifier would only work during low fire but not high fire.

I attached a diagram showing how I would wire a bypass humidifier with this furnace using the 2 stage setup.  I would use R to power the HUM STAT terminal.  This will tell the HUM dry contacts to close during a call for heat once the blower has started.  I'm not sure if you could jumper both W1 and W2 to the HUM STAT terminal without issues, but using only one would mean the humidifier would not work during one of the stages.  If you're using a single stage thermostat and auto staging then I would just wire the humidifier and solenoid in series with W1 and C, and ignore the rest.

Offline Porcupinepuffer

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Re: Installing basic humidifier in a Rheem with standard thermostat
« Reply #8 on: June 11, 2018, 06:29:56 PM »
So I re-wired it when I went back today. I started with the R to hum as it shows in their instructions and assumed that when they say the relay will only come on with 24v on th hum stat connection and "heat speed blower" that it would only work in the heating stage. But it will work during any moment the blower motor works. So with cooling and just regular fan ON, it will allow the humidifier to work. I very clearly get the audible thunk of the solenoid engaging. So since it's a single stage thermostat and the auto staging is set on the board, I just wired it from W1 to the hum stat so it would only work during heating. I'm assuming this should be good.

I had drawn out a diagram and it's identical to what you've posted except that I did use the add-on transformer. I had an empty L1 and Neutral stake on available on the board for the high voltage side, and ran one wire from the low side of the transformer to the solenoid, ran the other to the first hum terminal, then second hum terminal, then to the stat, then back to the solenoid... I think we're all good now. I just really don't want to rely on the customer to have to remember to turn off the humidistat and have it battling out a humidity war with the a/c.

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Re: Installing basic humidifier in a Rheem with standard thermostat
« Reply #9 on: June 11, 2018, 07:10:04 PM »
I have never worked on this furnace but thought the HUM dry contacts only closed if there was 24V on HUM STAT and the heating fan speed was running.  I wonder if you were using a 2 stage stat, once W2 became energized then W1 would de-energize and HUM STAT would lose 24V and the HUM dry contacts would open.  I wouldn't think we can jumper both W1 and W2 to HUM STAT without back feeding 24V.

It looks like this furnace is shipped with auto staging off.  S2-10 & S2-11 would both be off.  It's possible whoever connected it to a single stage thermostat may not have turned on the auto staging and the furnace is stuck on low fire.  If auto staging was on then your wiring should work as we would never get 24V to W2.

Offline Sergroum

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Re: Installing basic humidifier in a Rheem with standard thermostat
« Reply #10 on: June 12, 2018, 12:23:49 AM »
Are you certain that w2 gets de-energized during 2nd stage? For two stage cooling to work, both y1 and y2 needs to be energized. I would assume it is the same with w1 and w2. Are you certain the furnace does not need both Ws to be energized to kick into high stage?

I've jumpered R to w1 and w2 both before to initiate high stage immediately. Somehow I think w1 stays energized during high heat.

Offline Porcupinepuffer

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Re: Installing basic humidifier in a Rheem with standard thermostat
« Reply #11 on: June 12, 2018, 03:49:30 AM »
I had no issue with the humidifier coming on for heating, I just didn't want the humidifier coming on for cooling and/or the fan on. I did set the autostaging on the board s2-11 to ON since the stat is single stage.
I'm also curious about sergroum mentioning that both W's may be energized on second stage heating. I know the carrier's would require a jumper between w1 and w2 on the board to make it kick in to 2nd stage for high fire pressure adjustments.

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Re: Installing basic humidifier in a Rheem with standard thermostat
« Reply #12 on: June 12, 2018, 04:13:14 AM »
I would think W1 gets de-energized when W2 high fire gets 24V from a 2 stage thermostat. Regardless, if both W1 and W2 are energized with 24V, using a 2 stage thermostat, the furnace would only run in high fire and not low fire.  So if we jumpered both W1 and W2 to HUM STAT the furnace would be stuck in high fire.

Offline walker

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Re: Installing basic humidifier in a Rheem with standard thermostat
« Reply #13 on: June 12, 2018, 04:53:14 AM »
I would think W1 gets de-energized when W2 high fire gets 24V from a 2 stage thermostat. Regardless, if both W1 and W2 are energized with 24V, using a 2 stage thermostat, the furnace would only run in high fire and not low fire.  So if we jumpered both W1 and W2 to HUM STAT the furnace would be stuck in high fire.

It doesn't on these boards if you wire it w1 it also works in high fire.

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Re: Installing basic humidifier in a Rheem with standard thermostat
« Reply #14 on: June 12, 2018, 06:00:28 AM »
Even if you have a 2 stage thermostat wired to both W1 and W2?

Offline walker

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Re: Installing basic humidifier in a Rheem with standard thermostat
« Reply #15 on: June 12, 2018, 06:07:22 AM »
Even if you have a 2 stage thermostat wired to both W1 and W2?

Not sure, I'd have to try, 99% of the ones I work on have a single stage thernmostat or use the Econet thermostat.

Offline Sergroum

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Re: Installing basic humidifier in a Rheem with standard thermostat
« Reply #16 on: June 12, 2018, 11:33:16 AM »
If even a single furnace requires both W1 and W2 to be energized to kick into high fire, then I imagine 'none' of 2 stage thermostats  de-energize  w1 during high wire. And my experience states that that's the case. For high hire wire, at least for some boards, you need bot h Ws energized. So just using w1 and c for hum should  be working out. At least ... it has so far. Which is what made me wonder if I'm missing something.

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Re: Installing basic humidifier in a Rheem with standard thermostat
« Reply #17 on: June 12, 2018, 12:06:24 PM »
I'm talking about using a 2 stage thermostat and setup.  There would be no jumper between W1 and W2 if you're using a 2 stage thermostat.  The thermostat W1 is wired directly to the furnace W1 terminal and W2 is wired directly to W2.  On this furnace even if auto staging is on, if W2 is energized it goes to high fire.  So if you jumper W1 and W2 on a single stage setup your furnace is stuck in high fire.  With single stage you don't jumper W1 and W2 if you're using auto staging.  See the wiring diagram below.


Offline Sergroum

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Re: Installing basic humidifier in a Rheem with standard thermostat
« Reply #18 on: June 12, 2018, 12:39:11 PM »
Yeah. There is no jumper between w1 and w2.  Both w1 and w2 get power from the thermostat via individual wires.  The logic when the voltage gets sent is in the tstat, not the board.

So on stage one. w1 receives power from the 2 stage tstat.
On stage two, w1 and w2 get power from the tstat. Each via its own wire. Though the source comes from the same R.


I'll need to try when I get my paws on my next furnace. If two stage heating works like two stage cooling, then some furnaces upon receiving power to w2 will do ... nothing. They will only do something if they get power on 'both' w1 and w2 at the same time. At least that's how y1 and y2 works, no? Both terminals need to be energized.

Offline Porcupinepuffer

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Re: Installing basic humidifier in a Rheem with standard thermostat
« Reply #19 on: June 12, 2018, 03:20:06 PM »
Yeah I know carrier requires the R to be connected to W1 and W2 to force second stage heat... And I have been in some scenario's where the high stage cooling did nothing without the other Y energized... That particular furnace wasn't a Carrier, I think it was a rheem.