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Two Stage Furnace without W2 Connected

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#21 ·
cottora said:
hmmm. Somebody's Pug must have run away today...poor fella

I could phrase it differently if it helps:

I as the owner of the equipment would prefer a longer run cycle. I came to the board seeking advice as to what effect wiring a single stage thermostat to W1 when the manufactures instruction direct it to be wired to W2. I found this board via Google because it is advertised as a place where an Owner can ask the Pros for advise.

And you are incorrect sir, what I think is the only thing that matters. If I want to burn tires in my furnace to heat the house I can, I own it. I am looking for advise to help form my thinking...Thanks
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Thinking gets homeowners into trouble lots of times. Why do you think you need a longer run cycle? Im not suggesting that it should short-cycle, that is not good. The length of the run cycle has no direct tie to staging. The staging is done via a thermostat that calls W1 or W2 or by the board which runs a timer to activate W2.

What if your longer run cycle was detrimental to the equipment or to your wallet? What i would do in your case it to have a 2 stage thermostat installed and set up the furnace for true 2 stage operation. You may not get the longer run times you want, though.

P.S. you cannot burn tires in your furnace legally just because you own it.
 
Discussion starter · #22 ·
I hear ya. I am not necessarily saying my equipment has too short of a run cycle. I am trying to understand what actions are caused by my furnace having only the W1 connected when the instructions of the furnace state that if using a single stage stat to use only the W2.

I believe that if W2 was used then the furnace would kick to dual stage after like 15 minutes. But what happens on just the W1 connection? My guess is that the furnace runs on either low or high immediately when the call is made and never changes stages.

Thanks
 
#23 ·
Most every two stage unit I know of works on a time delay for second stage if wired only to W1. I believe the units I install (ruud) have to run about ten minutes before the second stage kicks in. I'd have to hunt up a diagram but I also believe many will also change blower motor speeds as well. Some units may have a means of adjusting low fire time.
I really can't see how much you would gain by a two stage stat.
 
#24 ·
as glennhvac stated.

when configured correctly on W1 alone the board calculates by timer when second stage should engage. if it's not set up for a single stage thermostat on the board then you will get only first stage. 1st stage alone may not heat the house adequately on the coldest days. you may also notice excessively long run cycles.

most boards have additional settings for stage delays times and blower speed adjustments.
 
Discussion starter · #26 ·
It is a RUUD Ultra Super Quiet 80 Two-Stage
Model # UGPR-07EBRQR

Under notes on the board layout it states "With single stage thermostat connect "W" to "W2" on IFC"

My single stage stat was installed connected to W (in case someone is just catching this thread)
 
#27 ·
w to w2 makes it fire in high (2nd) stage all the time. as it is only wired to W (W1) it is running in low (1st) stage only according to the note.
 
#29 ·
Powering w and w2 at the same time means high fire always. Powering w by itself will revert to a staged high fire determined by time. I install that equipment
 
#32 ·
yes. thanks to glennhvac's clarification -

only W will allow you to save a small amount of energy/fuel. Only W+W2 will set it as a single stage furnace. it would use the max all the time.
 
#33 ·
If only w is powered the furnace will come up to high fire after about ten minutes. I don't think anything will happen just powering w2 alone. Right now it's probably powering w and w2 on a call for heat. So you have basically had a one stage unit since the day it was installed.
 
Discussion starter · #34 ·
Sorry to kick the stuffings out of this dead horse and thank you all for you time! I am going to supply pics if that helps clarify anything. I believe the consensus is that my unit may be coming to high fire immediately (firing W and W2). Thanks

Also, I assume the below circled note means connection from Stat to IFC W2 and not Jumping W1 and W2 on the IFC??
Image

Image
 
#35 ·
connecting W to W2 will make it come to high fire immediately.

W by itself causes it to time the stages.

Connecting W to W and W2 to W2 from the thermostat to the furnace individually would mean you have a 2 stage tstat and not a single stage tstat.
 
Discussion starter · #36 ·
Thanks again for everyone help. I connected to W2 and the furnace does not fire at all with W2 wired only. When I connected back to W1 it fires as it has been. I have no idea why the service panel states to connect single stage stats from W to W2.

Ultimately Marc was right all along. Shouldn't have done any thinking on this...Cheers
 
#37 ·
The way I read it the 2nd stage NEVER fires the way it's currently hooked up. I see no option such as a DIP switch to tell the board if it's a single or 2 stage thermostat. The board has no way to know if a 2 stage thermostat is hooked up unless W2 is calling. not sure if W1 hooked to W2 causes high fire immediately or gives delayed high fire. CLOCK YOUR GAS METER and find out for sure how many BTU the furnace is burning. I highly suspect it's a typical oversized install where stage 2 is completely unnecessary. It does not surprise me one bit that the 42k low stage is more than enough to heat 1/2 of a 3100sqft house in Atlanta.
 
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#38 ·
54regcab said:
The way I read it the 2nd stage NEVER fires the way it's currently hooked up. I see no option such as a DIP switch to tell the board if it's a single or 2 stage thermostat. The board has no way to know if a 2 stage thermostat is hooked up unless W2 is calling. not sure if W1 hooked to W2 causes high fire immediately or gives delayed high fire. CLOCK YOUR GAS METER and find out for sure how many BTU the furnace is burning. I highly suspect it's a typical oversized install where stage 2 is completely unnecessary. It does not surprise me one bit that the 42k low stage is more than enough to heat 1/2 of a 3100sqft house in Atlanta.
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Again, the unit will fire on a time delay to 2nd stage after so many minutes if wired to W1. If you wire to W1 and W2 off a one stage stat it kicks in high fire. Another thread that was essentially answered on the first reply.
 
#39 ·
How does the board know if a 2 stage stat is connected and simply not calling for W2 vs. having a single stage stat hooked only to W1? Or does the board go into high fire after a delay regardless?
 
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#40 · (Edited)
Glennhvac said:
Again, the unit will fire on a time delay to 2nd stage after so many minutes if wired to W1. If you wire to W1 and W2 off a one stage stat it kicks in high fire. Another thread that was essentially answered on the first reply.
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I'm with 54regcab on this one. Hooking up only to W1 should cause that unit to only run in low stage. I don't think it has a timer or anything to kick it into 2nd stage. The only way 2nd stage can work is if both W1 and W2 are energized at the same time (by a jumper wire or a 2 stage thermostat). That's what the note on the schematic means. If you only have a single stage stat they want you to jumper W1 and W2 together to get maximum btus. Most of the commercial 2 stage rtu's that I come across are this way.

To the O.P... it sounds like your unit is oversized and is wired up to never run in 2nd stage, which is probably a good thing in your situation. If you do have a tech come out at some point, have them check to see what your gas pressure is set to. It could be that whoever installed your unit cranked the low stage gas pressure up to compensate for only having a single stage thermostat, which would basically accomplish the same thing as jumping W1 and W2. The gas pressure might be able to be lowered to give you longer run times. Like I said though, this needs to be done by a tech that knows what they are doing. Good luck.


edit... I just took another look at the wiring diagram that you posted. Since your unit has a 2 speed inducer motor, hopefully what I said about someone possibly cranking your low stage gas pressure up at some point to compensate for only having a single stage stat is wrong, because in that case your inducer would be running too slow. I'm guessing everything is fine how it is, but if you ever do have a tech come out it would probably still be a good idea to have him check the gas pressure to make sure it is set to it's minimum level. If you ever come to the point where you need a new furnace, get a proper load calc done first to find out the proper size that you need, so that your next furnace isn't oversized.
 
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