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

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.

"Robert11" wrote:

I guess what's confusing me is the "2 stage thermostat" part.

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.

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.

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.

"John Hines" wrote in message
...
"Robert11" wrote:

I guess what's confusing me is the "2 stage thermostat" part.

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.

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.

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.

I have a new two stage furnace running with a 1 stage thermostat. Way too
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

On Sat, 7 May 2005 14:07:53 -0400, "Robert11"
wrote:

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


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.

"JimL" wrote in message
...
On Sat, 7 May 2005 14:07:53 -0400,

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.



IAWTP

Robert11 ) said...

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 ?

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."
- Napoleon
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Calvin Henry-Cotnam wrote:
Robert11 ) said...

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 ?


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.

Hi,
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

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.

"MLD" wrote:


"John Hines" wrote in message
.. .
"Robert11" wrote:

I guess what's confusing me is the "2 stage thermostat" part.

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.

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.

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.

I have a new two stage furnace running with a 1 stage thermostat. Way too
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.

Yep, but that is the advantage of a full 2 stage install, it doesn't
have to fool around with such things.

BTW, have you compared the actual
room temp (at the stat) to the room temp reading displayed by the stat?

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