I've read the "benefits", and I've seen how mine is installed. But is
this really practical or at least optimal?
I have a 100 BTU furnace to heat 1700 sqr feet mainfloor and about
1300 basement (partially finished). The 2 stage functionality works
like this. I have a normal programmable thermostat. On the furnace
they installed a "timer". After the thermostate turns the furnace on,
it will run at low heat (3 burners) for 1 to 10 minutes (depending on
the manual setting of the timer). After that time it will kick into
high heat (2 more burners). It runs at high heat until the thermostat
kicks it off.
Theoretically, on milder days, the low heat will be enough and it will
never go into high heat. Then for the fewer cold days it will crank
up the heat. However, we set the temp to 65 for the night and 69 for
the day. So I can be sure that in the AM, it will crank up to high
heat to get to 69 as that will take 30 minutes or longer.
Does this really matter? Would a 2 stage thermostat make a big
difference? This all seems pretty questionable to me. Sounds like
On Thu, 13 Jan 2005 12:35:04 -0700,
nospam firstname.lastname@example.org wrote:
Who installed a timer on your furnace? Is your furnace new or some
pieced together self help project? 3 burners for 1-10 mins? What
controls that? Then 2 more burners?
At this point I have no idea what you have and Ive seen a lot of
Yeah, its all marketing hype. Keep your "project" just the way it is.
'I have a normal programmable thermostat. On the furnace they installed
I think by 'timer' , you mean an automatic Time Delay Relay (perhaps ?)
whereby the signal to the 2nd stage is delayed for 10 minutes.
'After the thermostate turns the furnace on, it will run at low heat (3
burners) for 1 to 10 minutes (depending on the manual setting of the
timer). After that time it will kick into high heat (2 more burners). '
From this description, it would only be possible if you had a split
manifold in your furnace with one gas valve controlling 3 burners, and
another gas valve controlling the remaining 2 burners. I doubt this is
what you have very seriously. Typically on a 2 stage gas furnace, you
would have ONE gas valve that works in 2 incremental stages : the first
stage produces a smaller flame thru ALL burners...then, when second
stage is demanded, the same gas valve would let more gas into the ALL
the burners thus increasing the flame (and hence , heat output) until
the thermostat is satisfied then all gas is shut off to the burners. A
2 stage setup is advantageous , especially in areas where there is a
significant milder winter period . Personally, a 10 minute time delay
before 2nd stage is engergized..is too short of a duration ; 15-20
minutes would be better to give low stage a chance to satisfy the
On Thu, 13 Jan 2005 16:28:50 -0600, email@example.com (Hello
Not at 6am on a butt-ass cold morning after you've programmed the
thermostat to go back to 62 or 64 degrees at night. In the morning,
you want that stat to kick in high immediately and stay there till its
warm. THUS, the need for a 2 STAGE STAT! If you dont have a 2 stage
stat you dont need a 2 stage furnace.
It's a Maytag 2 stage 80% eff, variable speed, 100btu, new furnace. I
posted previously with some related Qs, but this 2-stage stuff is
The "timer" (relay, delay, whatever) does this: The igniter starts,
gas is delivered to 3 of the 5 burners. After the time set on the
"timer" (1 to 10 minutes), if the stat is still wanting heat, the
other 2 burners will start.
Near as I can tell my "fan-only" blower speed remains the same during
"fan only" and low heat. The speed increases with high heat.
Without sitting around all day and watching and listening to this
think I cannot measure how ofter the low heat get the job done before
the high heat kicks in.
I guess waiting up to 10 minutes before the high heat kicks in is not
all that bad, although this seems pretty rudimentary, but I'm not sure
how a 2-stage stat could really be all that more intelligent. It
would come down to the stat having some kind of knowledge systems that
would tell it when to kick into high asap vs wait 5 or wait 10, etc.
It seems like the characteristics of the furnace, the current inside
temp, the outside temp, the desired temp, and the efficiency of the
furnace/ducting would all have to be constantly analyzed to sort out
the best approach. Seems like too much to ask of a $100-$200 piece of
On a somewhat related note, how can I tell what fan speed my blower
should be set at? I guess there are like 10 low/high settings. I'm
currently 2 down from the highest output.
Some (well at least one :) ) simply look at the temperature differential
(setpoint-actual) and the rate of change of the actual and use that...if
delta_T is so big, then both stages or if dT isn't quite so big but T
isn't catching up, etc...is an application of "fuzzy logic"
algorithms....whether it is any more efficient in the end, I have no
data to help...but it doesn't use any additional inputs, just a simple
microprocessor and some logic.
Don't recall which thermostat used it, saw it in a new product section
in a mechanical engineering trade mag some years ago...
If you look at the manual that came with the furnace you will note that
there are some very small switches called "dip switches" the "On-OFF"
settings of these switches dictate (at least on my Trane furnace) how the
furnace will operate---Motor speed time delay: that is,:how long at low
speed before ramping up to high etc. The manual shows a number of switch
combinations and what function(s) it will perform. The default settings are
On Fri, 14 Jan 2005 01:45:01 -0700,
nospam firstname.lastname@example.org wrote:
I can honestly say Ive never seen this in a new furnace yet and I
think Ive seen every residential furnace. All the burners fire on low
or high. 3 of 5 burners dont burn unless 2 are stopped up.
The only relays/timers/delay that control this are on the main circuit
board of the furnace.
and if you do know this answer then I will know you have NO LIFE.
A 2 stage manual mercury stat will sense the temp in the home and turn
on one or both stages as it feels is needed by sensing actual room
A digital thermostat will basically do the same with a little more
algorithm knowledge of its own.
By knowing the proper temperature rise of your furnace, the actual
heat stage you are in and the proper gas pressure and mixture.
Look around a bit, lots of people have asked the same questions.
The 2 stage thermostat basically decides if high heat or low is
(as opposed to the furnace timing out to high from low)
Depending on the heat loss of a house, you might short cycle
the furnace too often (not good) plus the temp variance would
be noticable (not good either)
Lets say it takes 11 minutes to heat the home from 64 - 66
after 10 the unit kicks into high. Its basically putting the
unit into overdrive and then boom, its off. Over and over
isnt a good thing, plus it wastes energy to boot.
Another advantage is this.... When you have a call
for heat from say 60 - 68 it should go right to high
and then within a 3 degree range (65) it go to low and slow the
heat process down to the desired range. Makes it much more
I have a 2 stage furnace and love it. (Once I had the
thermostat dialed into my preferences)
I personally use Honeywell thermostats (I have the new
touch screen series, its freekin cool lookin) and they served me
well so far. Check out ebay for 2 stage units
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