Just wondering if anyone has replaced their conventional furnace /
HVAC fan motor (PSC, single phase, etc) with one of the new ECM motors
to realize a reduction in your electricity bill.
Does anyone know what the "over-the-counter" cost is of these motors?
Also, do ECM motors generate electrical or RF noise that is either
radiated by the motor or fed back into the household wiring, thereby
messing up AM radio reception?
What is an ECM motor?
Just a few thoughts.
Most conventional induction motors don't get that warm, so how much
electricity are they wasting?
Also; let's say that it is a 200 watt (quarter horsepower motor?) and
you can 'save' one quarter of that consumption.
Also the motor runs half the time?
So saving = 0.05 kilowatts x 24/2 = 0.6 kilowatt hours per day.
At 10 cents per k.watt.hr that = 6 cents per day. Roughly $25 per
Versus cost of new motor?
On other hand that 'wasted' electricity is dissipated within the house
as heat so the furnace would have to run a few more minutes, burning a
little more oil/gas each time to compensate?
Might realise more gains by making furnace itself more efficient?
But the motor is outside the conditioned-air area, so it won't affect the
Assuming the motor costs $200, according to your calculations you would
break even in only eight years.
However, there is the opportunity cost to consider. $200 in a savings
account instead of a new motor, at 6% interest, generates $12 per year,
making the savings only $13. At that rate, the break-even point occurs in
Then there's the labor to install the motor, increased taxes, and other
Arghh! I read 200 watts as 200 dollars. Sorry.
Multiply all my calculations by three (45 years to recover the expense). As
for your actual question, I guess I could get a $600 motor for $200 from
someone who was silly enough to attempt this project.
They don't get warm because in a furnace, they're constantly being
cooled by the return airflow hitting them.
In general, from what I've read, a 1/4 to 1/2 hp PSC furnace motor is
shedding 150 to 300 watts of heat energy when in use.
At 100% efficiency, 1 hp = 746 watts. Since efficiency falls with
motor size, a 1/4 hp motor is at best 50% efficient (see reference
below). So it's consuming 373 watts (and shedding 186 watts as heat).
I pay 10.6 cents per kw-hour (about 60% of that is for the electricity
itself, and the other 40% is for other charges related to it's
delivery to me, as well as gov't taxes). In the summer, I'm running
my furnace fan constantly. For the average month, that's 730 hours.
For a motor that's using 373 watts for 730 hours, that's 272
kw-hours. At 10.6 cents per kw-hour, that's $28.83 per month.
Given a usage profile that has me running my fan for 100% during July
and August, and tailing off to 20% in February, I project an average
monthly usage of 49% for the entire year. That's about 4300 hours,
which works out to 1600 kw-hours, which works out to $170.
So if I had a conventional 1/4 hp PSC fan motor (50% efficient)
running for 4300 hours per year, I'm going to pay $170 per year.
If the motor was 100% efficient, I'd be paying $85 - saving $85 per
At best, for an ECM motor, I'm going to increase my efficiency by 25%
(to 75%), so I'm going to save $42 per year.
I'd be saving more if I had a bigger motor, possibly saving $85 per
year if this was a comparison using 1/2 hp motors.
So what is the "over-the-counter" cost of a single speed 1/4 or 1/2 hp
Are there any HVAC jobbers here that can answer that?
Good information really starts on page 13.
Capacitor-start, 4-pole motors have efficiencies from 50% to 65% (1/4,
1/3 and 1/2 hp) with efficiency increasing along with motor hp.
Most fan usage happens in conjunction with household cooling - not
During the non-heating seasons you are going to be running the fan -
sometimes without the A/C going.
I estimate that out of my hypothetical 4300 hours of fan use per year,
1640 hours will happen with the furnace on (about 38% of the time).
Where I live, the climate is similar to Detroit, Buffalo or Toronto.
Further south, more fan use will be for cooling than my projection of
62%. Based on this, the heat shed by the fan motor is not beneficial
or desirable most of the time.
The motor is *inside* the house. And it's placed directly in the
circulating air stream. So of course 100% of the heat it's shedding
will be transfered to the interior of the living space of the house.
Assuming my savings are between $40 and $80 per year (say, $60) and if
the motor costs $180 then it will take 3 years for payback. If the
motor is $240, then payback will be 4 years. If the motor is $480,
then payback will be 8 years.
The idea of earning interest on the money is nice, except that most
likely electricity costs will likely also rise, perhaps in a similar
way as your proposed 6%, so the opportunity cost factor will be a
wash. Especially given the volitile nature of the stock markets, and
declining interest rates. The S&P is up only 4.5% now vs the start of
That was going to be done by yours truly, so that's not a factor.
Don't forget that interest is taxable, not to mention that a 6%
savings account is not realistic. Bankrate.com says CD rates are
still around 5% but likely to drop soon; a savings account would be
Figure 4% savings account, 28% tax bracket. Interest that you get to
keep is $8 times 0.72 a year, $5.76, so the savings would be $19.24 a
year and the payback period would be ten years and a few months.
Unless, of course, you're able to take advantage of some program that
subsidizes replacing inefficient equipment with efficient equipment.
Then the payback would be shorter.
Stan Brown, Oak Road Systems, Tompkins County, New York, USA
I don't think he was talking about the electronics of the motor.
Conventional motors were either ON or OFF and coincided with heat or cooling
on or off with a thermostatic delay. The newer ECM motors have a control
panel that changes the speed of the blower but at the same time controlling
the furnace heat output or the A/C compressor speed. Usually it is just a
two stage where there is a low and a high heat or A/C. I don't think you'd
get the full benefit by just switching motors if it didn't match the control
panel, burner and compressor.
Rapid Realm Technology, Inc.
As part of OEM equipment built into a furnace, an ECM motor will be
connected to a control panel.
As a replacement part bought over-the-counter, they most probably will
not come with any such panel.
There will most certainly be more connections on them for wires other
than household 120 AC power.
There may also be dip-switches or jumpers on them. Presumably it
would also come with a data sheet or wiring diagram.
An HVAC maker can choose to use an ECM motor as a single-speed, or
maybe 2 speed, or continuously variable speed while at the same time
altering the heat output of the furnace (or changing the speed of the
compressor for AC) if they want to modulate the heat output of the
furnace and modulate the blower fan speed at the same time.
But it's still the case that an ECM motor is touted as being more
efficient *at all speeds and loads* compared to a PSC motor.
So even if I just use an ECM motor as a drop-in replacement for a PSC
motor, and wire the ECM motor for single-speed operation (which
theoretically shouldn't require an external controller board), then I
should realize some savings on my electrical bill.
And if I have the knowledge, I can rig my own control method such that
I can vary the fan speed at will. I could, for example, rig a pot or
a switch beside my thermostat so when I'm running the fan only for
circulation, I can turn down the speed (and realize even more savings
when compared to my PSC motor).
If my current HVAC setup is operating such that I would not gain any
increase in "comfort" by having a variable-speed blower fan, then a
variable-speed motor would not be of any interest to me.
However, ECM refers to a particular type of motor technology. ECM
does not defacto mean variable speed. PSC motors can also be rigged
for variable speed operation too (with the appropriate external
The issue of a controller board keeps cropping up in this thread, and
it's a red herring.
an ECM motor which is first rotated at a slow speed, then powered off and
the coast-down is timed to determine the air resistance of the duct system.
From that information the controller determines the RPM necessary for the
desired airflow and controls the motor at that airflow. The programmable
parameter is CFM instead of RPM.
When it went bad, the wholesale cost of the complete motor was about
$900.00. We located a replacement control module (which was a part of the
motor) for about $400.00. This controller board (and motor) is absolutely
required for this system to function as designed. Replacing the motor with a
different type would also require replacement of the entire furnace
controller board since the furnace controller depends on the RPM data from
the motor for its operation.
Conventional small AC motors (fractional HP motors) are VERY
inefficient at converting electricity into motion. I've seen numbers
around 50% efficiency.
Many new furnaces today come with ECM motors because furnace fans run
longer (higher duty cycle) in modern HVAC systems today vs 20+ years
If the cost of an ECM motor is, say, less than $200 (for the
do-it-yourself-er) then it's highly likely that just replacing a
conventional AC motor with an ECM motor in an existing furnace would
pay itself back in 1 to 2 years - plus you have the existing motor as
a backup if or when the ECM motor breaks down.
There are many mid-efficiency (80%) furnaces out there that DON't have
ECM motors, and there are many older furnaces that with simple
additions and modifications to intake and exhaust ducting (and by
turning down the burners and adjusting the burner primary air baffles)
can bring them to near 80% efficiency. You can convert a 30-year-old
60% efficient furnance to closed-combustion with some ducting and
modification to the cabinet's venting for example.
Nobody's posting any over-the-counter or "cash'n'carry" prices for
these motors on their websites.
I don't think too many of them are being sold for retro-fit or
In fact, there may even be supply shortages such that all production
is going straight to HVAC manufacturers.
My experience with electronically-controlled, variable-speed AC motors
(that you find in some treadmills and science-labs fume hoods) is that
they are extremely noisy (EM/RF noise) and without a lot of filtering
they inject a lot of noise back into the main supply wiring.
If there is a lot of high-current switching going on inside an ECM
motor, then I would think they too would be electrically noisy.
This furnace "modification" suggestion sounds very dubious and full of
obvious and potentially serious drawbacks to me. Like people
screwing around and winding up killing a house full of people with CO
or fire. If you have a 60% 30 year old furnace and it's worth
increasing it's efficiency, then it's worth getting a new furnace.
Not really. You can create a closed-loop for the intake air very
simply with the appropriate additions of ductwork that takes outside
air directly into the cabinet and sealing the cabinet so that the
combustion side can't mix with household air. The secondary flue air
intake (directly below where the flue starts) can also be sealed and
ducted so that it pulls air from a dedicated outside supply duct and
not from household air near the furnace. So in this scenario no
outside air can enter the house through the flue, and no combustion
products or gasses can enter the interior air of the house.
That is exactly what mid and high efficiency furnaces do, and there's
no reason the same mods can't be done with low efficiency furnaces
that are 20+ years old.
You're actually making it safer by creating a closed loop. By doing
so, there is no way that the blower can suck air back through the
flue. Given an un-modified low-efficiency furnace, that's exactly
what can happen if the house is sealed too tightly and too many
exhaust fans are operating in the house.
The furnaces made today are riddled with problems with short-lived
heat exchangers, sensors and electronic controllers.
Have a look at this site for an example of a poorly-designed secondary
It's generally accepted within pro hvac circles that there are many
new components, ideas and manufacturing techniques cropping up in
furnaces over the past few years that don't have the benefit of years
of field longevity and durability testing.
No it isn't generally accepted. What you're referring to isn't
unsolved problems, what it's called is "planned obsolescence". If it
doens't break they can't sell you a new one. The hvac industry is a
relative late-comer to that game, thats all.
When you're designing for planned obsolescence (as you unflatteringly
suggest the HVAC industry is doing) you sometimes overshoot your goal
and create something with a much shorter lifespan than was intended.
Again I point to this as an example:
And being a "late-comer" to the business of designing for planned
obsolescence, they are getting it wrong in some cases.
Which is a result of coming up with "new components, ideas and
manufacturing techniques over the past few years that don't have the
benefit of years of field longevity and durability testing."
All in all, it doesn't say much for your profession when you are so
quick to advise a home-owner spend $4k on a new furnace when-ever a
$150 motor or $350 controller board burns up (or when a home-owner is
considering improving the efficiency of an existing furnace) -
especially when you admit that new furnace designs are intended to be
inferior to older models.
I didn't say that it was a conscious descision. Big business is like
the rapids and its descision makers like the people riding them--
everyone is holding on for dear life and each is afraid to rock the
boat. The business has a life and a will of its own.
The link you keep posting means nothing to me. I've yet to encounter a
cracked heat exchanger on one of those models. Not to say they don't
exist. If I had some actual details of the complaints I'd be better
equipped to discuss that problem. AFAIK, the hearing hasn't even been
held yet, so no final decision. I think you're arguing apples and
oranges there anyway. How many class action suits are there currently
across all industries? How many are the result of failures due to "new
and non field tested technology"? As I said, most products are
simply not designed with the idea of permanancy in mind. Leaking
coils, for instance, have nothing to do with new technology, it has
only to do with cheapening of the manufacturing processes and
reduction of raw materials.
Maybe, maybe not.
If you bought a commercial furnace that included one, the complete
assembly would have to comply with FCC regulations (or those of your
own national regulating body, if you're not in the US) regarding EMI
in a household environment, so you shouldn't experience any radio
On the other hand, if you just go buy some random motor that happens
to fit in your old furnace, you won't know 'til you fire it up.
Bert Hyman | St. Paul, MN | email@example.com
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