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

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?
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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 year? 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?
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terry wrote:

But the motor is outside the conditioned-air area, so it won't affect the heating/cooling.
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 fifteen years.
Then there's the labor to install the motor, increased taxes, and other variables.
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Where can you get a 600\$ vsdc motor for 200?
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ransley wrote:

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.
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HeyBub wrote:

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 year.
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 ECM motor?
Are there any HVAC jobbers here that can answer that?
------------------------
http://www.eere.energy.gov/buildings/appliance_standards/commercial/pdfs/small_motors_analysis.pdf
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 heating.
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 the year.

That was going to be done by yours truly, so that's not a factor.

Not sure what you mean by that.
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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 below that.
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
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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 anybody know how to use a web search tool?

Probably not; the motor is likely to be inside a metal housing.
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you need the electronics to run it, you cant just replace it my Lennox guy said
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ransley wrote:

I'm pretty sure that's not correct.
From what I can tell, all the electronics are inside the motor. You hook up the main AC supply directly to the motor, just like a conventional AC motor.
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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.
-al sung Rapid Realm Technology, Inc. Hopkinton, MA
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Alan Sung wrote:

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 controller).
The issue of a controller board keeps cropping up in this thread, and it's a red herring.
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There is obviously a lot of variation in ECM systems. My son's furnace uses 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.
Don Young
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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.

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 non-HVAC systems.
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.
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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.

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snipped-for-privacy@optonline.net wrote:

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 heat exchanger:
http://furnaceclaims.com /
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.
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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.
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hvacrmedic wrote:

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:
http://furnaceclaims.com /

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.
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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.
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snipped-for-privacy@Guy.net (Some Guy) wrote in

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 | snipped-for-privacy@iphouse.com

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