We just had a new Carrier Infinity 80% furnace installed. It has a two stage
heater and continuous fan. Our installer recommended against the special
Carrier thermostat because he says it's not worth it, and we were glad after
seeing the $250 price tag.
Anyway, the brochure states that the furnace is supposed to provide a "near
continuous flow of warmth in low capacity operation for a steadier, more
consistent indoor temp. Longer gentler heating cycles combined with lower
fan speeds help keep your utility costs low."
So we were expecting fewer temp swings, with lower heat coming on for longer
periods. And we do run the fan constantly.
So far, this new furnace has operated exactly like our 20 yr old furnace:
heat coming on full blast, then cycling off for half hour or so, before it
kicks in again and does the same thing. And our installer said that after so
many minutes of the furnace kicking out heat, it'll go from low heat to high
heat. But I don't feel any noticable change in the temp of the heated air
after the furnace has been running for a long time.
It has been cold outside since we had the furnace put in, with the outside
temp being -10 to +20 outside, so is that why we are feeling high heat
cycling on and off all the time rather than the more prolonged low heat?
Even so, the heat will cycle off for 30 minutes between cycles. Then I just
feel the fan pushing air out of the vents that seems to be room temp. Will
the "nearly continuous" low heat feature be more noticable when it warms up
Anyway, how is the continuous fan and two stage heat settings supposed to
work if you don't have the special Carrier Infinity Thermostat? Will it work
OK without the big-buck thermostat, or is the only way to get that near
continuous flow of low heat to get the Carrier thermostat? Or does it sound
like it should work fine with a regular thermostat but that our installer
doesn't have the furnace's settings correct?
Any advice would be appreciated!!
Yeah, it's pretty steep for what it does. There are much cheaper
aftermarket units that evidently do the same stuff.
He should've left the installation manual with you. Dig in. Without
the Carrier Infinity stat (identical to my overpriced Bryant Evolution
control I believe), at least on my 94% 2-stage unit, the CPU in the
furnace controls this stuff.
It's entirely possible the installer screwed up a dip switch setting
and it's firing on one speed only. But, it's also possible though
that your heating needs right now are such that high heat is being
called for, based on the CPU's stored run history. Is it cold there
now? How long are your heating cycles?
On my Bryant high efficiency furnace installed a few months ago,
there's a switch SW1-2 for "adaptive heat mode." described as "allows
2 stage operation with a single stage thermostate. Turn on when using
2 stage thermostat to allow low heat operation when..."
The description the installation manual for my furnace says that in
the absence of a 2-stage stat, and in adaptive heating mode,
V. Sequence of Operation
A. Single stage thermostat and two stage heating (adaptive mode)
NOTE: This furnace can operate as a two stage furnace with a
single-stage thermostat because furnace control cpu includes a
programmed adaptive sequence of controlled operation, which selects
low-head or high-heat operation. This selection is based upon the
stored history of the length of previous gas heating periods of the
single stage thermostat.
Your mileage may vary, but I wouldn't be surprised if yours works very
So, if you're really hearing only the 2nd stage and high fan speed
when yours kicks on, it could be because adaptive heating mode is
disabled by this switch being on (or its analog on your furnace) or
because run time was such in prior cycles of operation that high
output got selected, and because of the CPU's algorithm and
hysteresis, it's selecting the high setting because it hasn't
encountered a short enough run cycle to tell the CPU to do anything
On mine at least, if you power down the system, it resets/erases the
history, and wll start on low heat mode and stay there for up to 16
minutes before going to high if needed.
If I were in your position, I'd look for the relevant portion of your
own install manual, eyeball the switch settings, and if you can
confirm the adaptive heat mode isn't set correctly for a 1-stage
t-state definitely get the installer back out there to fix his
installation. If you still can't figure out why you're always seeing
high heat, hell call him anyway, other things could be wrong
(including "they may have undersized the entire unit").
Hope that helps some.
Thanks for the advice, Todd. I dug out my furnace install manual, most of
which I don't understand, and saw the same explanation as you quoted. I also
powered down the furnace and restarted, and for the first time felt the low
heat coming out of the vents. So if that worked, then I'm guessing the
switch is correct and the only reason it's always on high heat is because of
the cold outside temps.
Glad to hear I don't have to buy a new expensive thermostat!!
Yeah, your conclusions make sense to me--"normal operation."
After enough cycles of low-heat timing out to engage high-heat (to
keep up with your desired temperature), I suspect that the furnace
will begin starting immediately on high heat again, and you won't see
a low heat cycle until the weather warms up enough such that your
high-heat-only cycle times get too short for its liking.
The only thing I'd be concerned with potentially is that if it's not
_that_ cold outside for your area, and/or your furnace seems to be
running really long cycles or almost continuously, I'd be concerned
that the installer put in an undersized furnace.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.