Author Topic: Two Stage Thermostats for Two Stage Furnace  (Read 12797 times)

Offline lymer

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Two Stage Thermostats for Two Stage Furnace
« on: September 24, 2015, 04:13:37 AM »
I am having a two stage furnace installed to replace an old single stage.  I purchased a programmable thermostat years ago, model Honeywell CT3200.  I am 99% certain this thermostat is not really compatible with the new two stage furnace I am having installed.  My contractor insures me it isn't necessary to purchase a new T-Stat.  Research on the topic suggests to me that a single stage thermostat can be rigged in such a way to work with a two stage systems, but that this may not be the most desirable situation for reasons often unclear to me.

Opinions One:
I am shortchanging, in some significant way, the advantages of a two stage furnace wiring it to a one stage thermostat?

Presently,(Single Stage Furnace), my thermostat wiring is basic and has only four telephone typed gauge wires.  Green, Yellow ,Black and Red.

Opinions Two:
If I choose to use a two stage thermostat, do I have to fish through my walls additional wires OR Can I not just use the existing four wires and wire differently.  Other options that do not force me to fish wires through my walls?

Thanks


Offline Admin

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Re: Two Stage Thermostats for Two Stage Furnace
« Reply #1 on: September 24, 2015, 04:09:08 PM »
If you install a 2 stage thermostat it's unlikely it will save you what the thermostat has cost you.  Using a 2 stage thermostat would improve comfort but not efficiency.

Any two stage furnace will have a control board that can be adjusted to use either a single or 2 stage thermostat.  The control board will simply time the second stage if you use a single stage thermostat.  I honestly doubt the average person could tell whether their furnace was controlled by a single or 2 stage thermostat.

Most 2 stage thermostats would require a W2 and common wire and would need at least 6 wires.

There are controls that only require 2 wires to the thermostat, but require an additional module installed at the furnace to make things work.  You could look at getting the Honeywell Prestige 2.0, which only needs 2 wires but can control a 2 stage furnace, AC, HRV and humidifier.  It also has the option to be controlled remotely by using an app and the Redlink gateway system.

Offline lymer

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Re: Two Stage Thermostats for Two Stage Furnace
« Reply #2 on: September 25, 2015, 04:10:21 AM »
"Any single stage furnace will have a control board that can be adjusted to use either a single or 2 stage thermostat.  The control board will simply time the second stage if you use a single stage thermostat."

Did you mean to write that any two stage furnace will have a control board that can be adjusted to either a single or 2 stage thermostat.  Presently I am taking away from your comment that the control board of a two stage furnace can be adjusted to to time the need for the second stage.  (IE) After 12 minutes if desired temp set by your thermostat is not reached the second stage kicks in until it is.

"Using a 2 stage thermostat would improve comfort but not really efficiency"

How do you believe comfort would be lost if wiring the two stage furnace to a single stage thermostat?

Lastly, I have not trouble with losing a little efficiency and agree it may never equal the cost of a new thermostat, especially the Honeywell Prestige 2.0, but I do not wish to impede the function of the furnace in such a way that either the manufacturer has a reason to void my warranty or the unit prematurely breaks down because it has been set up within the control board to operate in such a way that it was not designed to.

Perhaps these are sill stupid questions, but my thought was I do not wish to merely save a few bucks on a thermostat if (1) I am losing comfort in some major way OR (2) Doing harm to the furnace by not installing a two stage thermostat

Thanks

Offline Admin

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Re: Two Stage Thermostats for Two Stage Furnace
« Reply #3 on: September 25, 2015, 05:47:15 AM »
Yes, I meant to say any two stage furnace...

Using a 2 stage thermostat will not harm the furnace.  And because the control board is compatible with a single stage thermostat, the furnace will still operate both stages.  The control board would, as you say, start the second stage after about 10 minutes.  You won't notice a difference between the control board or a 2 stage thermostat controlling the furnace.

Unless you purchase a expensive thermostat or upgrade the wiring I would just stick with a single stage thermostat.

Offline Trainerguy

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Re: Two Stage Thermostats for Two Stage Furnace
« Reply #4 on: September 25, 2015, 01:21:36 PM »
The only real complaint I have received from customers regarding the use of a single stage programmable stat on a two stage furnace is that in the morning, the time to bring the house up to temperature takes too long.
The reason for this is that the control board in the furnace brings the first stage of heat on first at a lower btu output and and will continue this way for 12 minutes. After that time lapse as long as there is a call for heat, the board will then call for the gas  valve to open fully and the full btu output of the furnace will be used, The temperature will rise in the house until it reaches the setting of the stat.
By using a two stage stat, in the morning when the stat calls for the temperature to be brought up to the programmed temperature, the second stage of the stat will be calling for the full output of the furnace immediately thus raising the temperature much faster.
The use of the two stage stat requires an adjustment of a switch on the control board.

Trainerguy

Offline harshal

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Re: Two Stage Thermostats for Two Stage Furnace
« Reply #5 on: September 25, 2015, 07:40:13 PM »
I would tell the customer to use the programming options, as even with single stage thermostat it would reach the require temperature at that specified time.

Offline walker

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Re: Two Stage Thermostats for Two Stage Furnace
« Reply #6 on: September 27, 2015, 04:02:10 PM »
The only real complaint I have received from customers regarding the use of a single stage programmable stat on a two stage furnace is that in the morning, the time to bring the house up to temperature takes too long.
The reason for this is that the control board in the furnace brings the first stage of heat on first at a lower btu output and and will continue this way for 12 minutes. After that time lapse as long as there is a call for heat, the board will then call for the gas  valve to open fully and the full btu output of the furnace will be used, The temperature will rise in the house until it reaches the setting of the stat.
By using a two stage stat, in the morning when the stat calls for the temperature to be brought up to the programmed temperature, the second stage of the stat will be calling for the full output of the furnace immediately thus raising the temperature much faster.
The use of the two stage stat requires an adjustment of a switch on the control board.



Trainerguy

12 minutes??? it depends on the furnace, some have a 5 or 12 minute option, some have a 10,15,20 option, some have a 5 minute or an auto option.

Not all 2 stage tstats will call for the 2nd stage heat immediately, it depends on how much of a climb in temp is being called, if it only needs to go up 1 or 2 degrees it may start up in first stage, if it's calling for a 3 degree rise or more then probably go straight in to 2nd stage heat. depends on the tstat though.

Some thermostats will have an option to have your house at a desired temp at that time, and not just turn on at that time, some also build algorithms internally that will time how long it takes to get to that temp based on past experience and will have the house at the desired temp at the desired time.

there are a plethora of different options to get the customer the comfort they desire.

Offline 44trane

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Re: Two Stage Thermostats for Two Stage Furnace
« Reply #7 on: December 22, 2017, 09:12:11 PM »
Lyric T5 vs T6 controlling my two stage furnace:

I asked Honeywell and received this response:

"The T5 will uses a algorithm to control the electric backup.

The T6 would be the better option as it allows more control option that you can set. that will let you have a say over how and when the 2nd stage comes on."

I have two questions:
What is "electric backup" and it sounds like this implies that the T5 would not give me the complete control I need? 

This furnace I had installed in August is very noisy in stage 2 and it spends most (80%) of each cycle in stage 2 at average winter temps (about 5-10 degrees below freezing).  It doesn't matter where you are in the house; you can tell when the furnace is on.  It has not improved the comfort level as was promised.  I need to extend the time spent in stage 1.

Offline walker

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Re: Two Stage Thermostats for Two Stage Furnace
« Reply #8 on: December 22, 2017, 09:16:10 PM »
Lyric T5 vs T6 controlling my two stage furnace:

I asked Honeywell and received this response:

"The T5 will uses a algorithm to control the electric backup.

The T6 would be the better option as it allows more control option that you can set. that will let you have a say over how and when the 2nd stage comes on."

I have two questions:
What is "electric backup" and it sounds like this implies that the T5 would not give me the complete control I need? 

This furnace I had installed in August is very noisy in stage 2 and it spends most (80%) of each cycle in stage 2 at average winter temps (about 5-10 degrees below freezing).  It doesn't matter where you are in the house; you can tell when the furnace is on.  It has not improved the comfort level as was promised.  I need to extend the time spent in stage 1.

They probably thought you had a heat pump with auxillary electric heat strips.

Offline 44trane

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Re: Two Stage Thermostats for Two Stage Furnace
« Reply #9 on: January 10, 2018, 11:24:27 AM »
SUCCESS!
I have installed the Lyric T5 to control my two stage Trane 80K BTU furnace.
I had the tech install a six wire cable when they installed the new furnace.  I am using the black wire for the W2 at the thermostat.

I attached the black wire to W2 at the furnace and removed the jumper between W1 and W2. 

So in the morning when the temp needs to rise from 15ºC, the T5 thermostat calls for auxiliary heat (W2) and it kicks on stage 2.
Once the house temp has risen to within 1ºC of the setting (19ºC), it drops back to stage 1.  The rest of the day it runs on stage 1 only.  The furnace is a lot quieter during the day now since it never goes into stage 2!!

I showed my son how to do the same on his Rheem 85K BTU furnace.  So you don't need a Lyric T6 to control a two stage furnace.