Has anyone ever replaced their conventional furnace fan motor with an ECM motor?

Posted by Some Guy on December 21, 2007, 9:09 am

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?

Posted by AZ Nomad on December 21, 2007, 10:14 am

>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.

You'll never recoup the cost. Wait for the unit to wear out and then replace
it with something more efficient. If the entire unit is hopelessly inefficient,
then retrofitting makes no sense; replace the entire unit.

>Does anyone know what the "over-the-counter" cost is of these motors?

Does anybody know how to use a web search tool?

>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?

Probably not; the motor is likely to be inside a metal housing.

Posted by Some Guy on December 21, 2007, 10:34 am

AZ Nomad wrote:

> > 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.

> You'll never recoup the cost. Wait for the unit to wear out and...

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
ago.

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.

> If the entire unit is hopelessly inefficient,
> then retrofitting makes no sense;

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.

> > Does anyone know what the "over-the-counter" cost is of
> > these motors?

> Does anybody know how to use a web search tool?

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
non-HVAC systems.

In fact, there may even be supply shortages such that all production
is going straight to HVAC manufacturers.

> > 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?

> Probably not; the motor is likely to be inside a metal housing.

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.

Posted by Bert Hyman on December 21, 2007, 10:21 am

> 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?

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
interference.

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 | bert@iphouse.com

Posted by on December 21, 2007, 11:15 am

>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?

It sounds like a tumor transplant to me. I put a regular motor in my
Trane air handler when the ECM motor went bad. They wanted over $1000
for the motor. Nobody could convince me I was going to save $125 a
year with this (the original lasted 8 years)

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