Furnace Thermostat: Meaning Of "2 Stage" ?

Hello:
A bit confused over the terminology on furnace thermostats. Embarassed to ask, but really want to be sure I have it right.
Does a 2 stage furnace (where there are two gas valve settings; a high heat and a lower heat output) require a 2 stage thermostat ?
I guess what's confusing me is the "2 stage thermostat" part.
By 2 stage on the stat, do they, perhaps, just mean a programmable setback temp., or is it really that you need this type to control (properly) a 2 stage furnace such as the Trane gas, forced hot air furnace I will be getting installed shortly.
Might anyone please explain this a bit.
Thanks, Bob
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By 2 stage on the stat, do they, perhaps, just mean a programmable setback temp., or is it really that you need this type to control (properly) a 2 stage furnace such as the Trane gas, forced hot air furnace I will be getting installed shortly.
Bob - Keep in mind Im not an HVAC guy, just another homeowner. But yes - to answer your question - you most definately need a 2 stage stat. It's not a setback. For a 2 stage furnace to work fully as designed, the thermostat is the guy who needs to make the call as to wether or not its time to bump up to stage 2.
Don't let the installers mislead you on this - on my furnace, and I *guess* any other 2 stager, the jump to 2nd stage can be a timed event, based upon dip switch settings.
For some reason, it seems to be very common for installers to put in a 2 stage furnace, and skip the stat, so I'd recc. you stress to the installer you want the stat controlling the stages.
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A thermostat which has controls for the additional heater stage. This requires additional wires in the bundle, so unless they replace the existing wires, something else has to be done.

I paid extra to get a good tstat to go with my new Lennox last fall, with the new wire pull and all. Temp stayed right on the money all winter.
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wrote:

much of a job to get the extra wiring between the two units to put in a 2 stage stat. This doesn't impact the temperature holding capability of the stat. Control of the temperature was also right on the money. Instead of the transition between stage 1 and stage 2 being programmed by the stat it is done via dip switches on a timed basis. BTW, have you compared the actual room temp (at the stat) to the room temp reading displayed by the stat? While the two stat readings (displayed room and stat setting) will agree there can still be an error between the actual room temp and the stat displayed room. My stat has the means to make an adjustment to compensate for any difference. MLD
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Yep, but that is the advantage of a full 2 stage install, it doesn't have to fool around with such things.

Yep, right on the money, all across the house. The variable speed blower, left always on, does wonders.
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wrote:

I prefer the standard single stage thermostat to go with a two stage furnace. It is telling the furnace you need heat and the two stage furnace then handles the transition between the stages just fine, without the additional expense and complexity of a two stage thermostat.
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IAWTP
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Robert11 ( snipped-for-privacy@notme.com) said...

Maybe in some cases, but I have a Carrier two stage furnace with a normal thermostat. When the thermostat calls for heat, the 60,000 BTU burner comes on. If the thermostat is not satisfied (meaning, the room temperature has reached the setpoint) within a certain amount of time, it automatically shifts to the "second stage" which means a second burner fires up to provide a total of 100,000 BTU.
Only on the coldest of days is the the full 100,000 BTU actually needed. There's probably a very small, if any, fuel savings since theoretically the house still has to be heated to the same temperature relative to the outside temperature. Losses due to inefficiency would be lower with the lower stage burner, so some fuel savings is possible.
It does improve comfort on the days that are not the coldest. On these days, instead of more frequent temperature swings from the full power coming on and heating up the home in a shorter time and shutting off, the lower stage can do a better job of regulating the temperature.
--
Calvin Henry-Cotnam
"Never ascribe to malice what can equally be explained by incompetence."
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Calvin Henry-Cotnam wrote:

That's right. Thermostat does not care whethere furnace is single or multi-stage. It just sets the desired temp. and when it's reached burner goes off. Stage control is within the furnace(processor logic controlled) Tony Tony
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I have a rheem two stage unit myself and originally had a single stage thermostat. I went for a nice honeywell two stage thermostat to take full advantage of the unit.
A two stage thermostat controls what heating is necessary in the house to get it to the preprogrammed temp (either high or low) The problems without a two stage thermostat is that the thermostat can short cycle a furnace. If it takes 12 minutes to heat the home and it runs on low for 10 and then kicks to high for 2, thats not good. No point in that one. With a two stage unit, generally if there is a 3 degree difference is what the house temp is and what you want it to be it should kick into high first, bring the house to almost temp then go to low and bring house to the desired temp. From there if the temp need to be maintained it uses low to do it. I can also set how many times I want the unit to allow the cycling of the furnace on and off. I have to have something go on 6 times an hour. (I feel there is more wear and tear) A good thermostat can adjust this setting.
As for not wanting to connect it because of the existing wiring??? Bah! Most wires that go down to the furnace are 5 wires. That's all you really need for a 2 stage unit (24volt (that's 2) furnace controls (another 3)) If you dont have it, you can eliminate the 24volt line and go with a battery operated thermostat.
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