Dual Stage Furnace

grod777 · 10-10-2011, 06:58 PM

I have a dual stage gas forced air furnace. The thermostat that was installed is not a dual stage model.
Is it necessary to have a dual stage thermostat for the dual stage function to work?
If not then why are there dual stage thermostats?

Marty S. · 10-10-2011, 07:04 PM

With a 2 stage thermostat second stage will be brought on by temp drop. With a single stage thermostat the furnaces second stage will be brought on by a timer. Both work but a 2 stage thermostat will run the furnace longer for better comfort.

raylo32 · 10-10-2011, 07:06 PM

I just installed one of these (2-stage var speed york) and you can run it off a 1 stage t-stat but will get only low fire heat. But that is silly. Just get a 2-stage t-stat, they are available anywhere.

One intersting aside to this are some of the modulating furnaces that can work off a 1 stage t-stat and run an on board algorithm to vary furnace output. This in lieu of using the specific modulating communicating furnace that the mfg sells which would take full advantage of the modulating feature... but not required to get some modulating benefit.

Quote:

Originally Posted by grod777

I have a dual stage gas forced air furnace. The thermostat that was installed is not a dual stage model.
Is it necessary to have a dual stage thermostat for the dual stage function to work?
If not then why are there dual stage thermostats?

grod777 · 10-10-2011, 07:13 PM

So a 2 stage t-stat will make it run better (efficient)?

I only ask because I was told it was not needed when the system was installed. Did not make sense to me. If I have a 2 stage furnace then why not a 2-stage t-stat.

raylo32 · 10-10-2011, 07:24 PM

Post your brand and size furnace. That will help folks give you a better answer. I know for mine running with a 1-stage t-stat with the default board setup would limit it to low fire so it would behave like a smaller furnace... and maybe not be able to keep the house warm on the coldest nights. Not sure they all work this way so you need to provide specifics.

My furnace does have a jumper that will provide some high fire capability with a 1-stage t-stat. With the jumper set properly it will kick in high stage after a set number of minutes in low fire. Yours might be set up like that. If so that would work OK, but not have as much control as with a 2-stage t-stat.

grod777 · 10-10-2011, 07:31 PM

It's Sears Branded, model is:
T8MPT075F14B1
This is not variable speed.

Not sure where to look for size n manual.

gregzoll · 10-10-2011, 07:43 PM

grod777, before I changed to the 3m Filtrete CM-50 (radio thermostat model ct-30), I used a Honeywell RTH63xx series for my 2 stage. Only reason I went with the 3m wifi thermostat, is so I have better control while away, and plus the last six months, up until I had surgery in August, I was pretty much bed ridden, or should I say chair ridden, due to a bad neck problem.

I love the wifi thermostat, which now I am running the Ourhomespaces.com radio in it, which is a better site, and app for the iPhone. I would not have it any way now, with being used to having a Internet enabled thermostat. Yes, I am a techie, and will wave my flag on cool technology.

grod777 · 10-10-2011, 08:09 PM

Quote:

Originally Posted by gregzoll

grod777, before I changed to the 3m Filtrete CM-50 (radio thermostat model ct-30), I used a Honeywell RTH63xx series for my 2 stage. Only reason I went with the 3m wifi thermostat, is so I have better control while away, and plus the last six months, up until I had surgery in August, I was pretty much bed ridden, or should I say chair ridden, due to a bad neck problem.

I love the wifi thermostat, which now I am running the Ourhomespaces.com radio in it, which is a better site, and app for the iPhone. I would not have it any way now, with being used to having a Internet enabled thermostat. Yes, I am a techie, and will wave my flag on cool technology.

Not sure how that pertains to me. My question was in regards to single and dual stage t-stats.
My local utility provider has a program where they offer free web enabled t-tats. That is why I am asking this question. I am not sure if the t-stats they provide are dual stage, so I wanted to know if I would be losing out on efficiency with a single stage t-stat.

raylo32 · 10-10-2011, 08:16 PM

I think you do not lose a lot of efficiency... you just don't have as much control as if you had a 2 stage stat. A true 2 stage stat shifts back and forth between the stages based on a temp differential (usually 2 degrees) between setpoint and actual temp. With a one stage stat it will use some other logic, like time running before shifting to high fire... assuming they have configured the board to provide staging with your one stage stat.

Quote:

Originally Posted by grod777

I am not sure if the t-stats they provide are dual stage, so I wanted to know if I would be losing out on efficiency with a single stage t-stat.

gregzoll · 10-10-2011, 08:27 PM

Quote:

Originally Posted by grod777

Not sure how that pertains to me. My question was in regards to single and dual stage t-stats.
My local utility provider has a program where they offer free web enabled t-tats. That is why I am asking this question. I am not sure if the t-stats they provide are dual stage, so I wanted to know if I would be losing out on efficiency with a single stage t-stat.

Actually it does, because you are asking for the difference. Simple answer, a 2 stage capable thermostat determines when the furnace/air handler will make the change, by using the differential and swing settings, such as the 3m 3m-50 & 3m-80 have. Vs. with using a single stage thermostat, the furnace uses it pre-programmed by the factory engineers to determine when to jump from Stage 1 to Stage 2.

Simple answer, go with a multi-stage capable thermostat, because you will see the savings after a couple of heating & cooling seasons.

grod777 · 10-10-2011, 08:39 PM

Quote:

Originally Posted by raylo32

I think you do not lose a lot of efficiency... you just don't have as much control as if you had a 2 stage stat. A true 2 stage stat shifts back and forth between the stages based on a temp differential (usually 2 degrees) between setpoint and actual temp. With a one stage stat it will use some other logic, like time running before shifting to high fire... assuming they have configured the board to provide staging with your one stage stat.

So you are saying that even with a 1 stage t-stat the furnace can still operate in 2 stages?

grod777 · 10-10-2011, 08:40 PM

Quote:

Originally Posted by gregzoll

Actually it does, because you are asking for the difference. Simple answer, a 2 stage capable thermostat determines when the furnace/air handler will make the change, by using the differential and swing settings, such as the 3m 3m-50 & 3m-80 have. Vs. with using a single stage thermostat, the furnace uses it pre-programmed by the factory engineers to determine when to jump from Stage 1 to Stage 2.

Simple answer, go with a multi-stage capable thermostat, because you will see the savings after a couple of heating & cooling seasons.

Understood. I was just not sure about the models you indicated.
My cooling i snot 2 stage though, only the heating.

gregzoll · 10-10-2011, 08:51 PM

Quote:

Originally Posted by grod777

So you are saying that even with a 1 stage t-stat the furnace can still operate in 2 stages?

Ding, ding, ding, we have a winner.

gregzoll · 10-10-2011, 08:54 PM

Quote:

Originally Posted by grod777

Understood. I was just not sure about the models you indicated.
My cooling i snot 2 stage though, only the heating.

Mine is the same way, but the thermostat I highlighted actually makes it more efficient, than the other that I was using, because you can set the stage differential on the 3m-50, vs the honeywell rth6300 series. Efficiency is about using the right equipment to do the job. This past Summer, once I got the new thermostat stabilized with the software I was using to monitor it, I moved the Swing to 1.5 (can not change different for heat or cool, so adjusted to 1.0 for heating), and differential for both heating and cool is the same, set at 3.0, I saw a very noticeable difference with cooling, with the single stage a/c we have. When I had to set for heat a week ago, along with making sure that we are ready for Winter, you can notice a change in operation, compared to the other.

I hated the honeywell, due to it was way too basic, in being able to fine tune it for more efficient operation.

grod777 · 10-10-2011, 08:59 PM

Fair enough. As long as I am utilizing the 2 stage function I am happy with that.
I have an email in with my Utility Co. to see if they offer a 2 stage model for the free program. If not I will go with the 1 stage. It's free and a huge convenience being able to monitor/control remotely.