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Converting furnace motor to ECM - where to start?

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Deal Guru
Jul 7, 2017
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Converting furnace motor to ECM - where to start?

I spoke to the sales rep of a local (and reputedly very reputable) HVAC dealer and service company who told me not to bother replacing the HP until it goes.

Since the HP and air handler may have another 5-10 years of life left, if not more (he used to install 80% Carrier back in the era when my current house was built and thinks it should last another 5-10+ years - circuit boards re what goes these days).

I've heard that savings from converting the motor from AC to ECM can be significant. Just wondering where and how to start? Size of the motor and mounts, and voltage as a start?

TIA
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Feb 11, 2007
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I've considered installing this Mars Azure unit, which seems like a good option and DIY'able.
Cost savings should be nice, plus variable speed means you can run it on low constantly, and keep temps around your house more comfortable and even.

It's $309 right now but has been under $260 last year.
https://www.amazon.ca/Mars-10860-Azure- ... B00O1566GW
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Im on the fence with one to. Current furnace is HE and 13 years old. Even on the cheap on Amazon, minimum $300 just for the motor. Im working on a air balancing issue with my furnance.

Ive got other cheaper options to do first before I do this

I currently have my fan ON all the time with a single speed motor. With the one month cold snap it helps with circulation and evening out heat between levels and as well as humidity. But Im scared to see my next electrical bill

To me I have the most non HE furnace out there. Its HE, but a single speed motor and not dual stage. Kind of an oxymoron on HE, but whatever

I have never replaced a furnace all these years of home ownership. What is the average cost? While putting in the motor is an idea, I could just put that money into a new furnace that has one already and dual stage. But that would the last resort kind of thing
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WikkiWikki wrote: Im on the fence with one to. Current furnace is HE and 13 years old. Even on the cheap on Amazon, minimum $300 just for the motor. Im working on a air balancing issue with my furnance.

Ive got other cheaper options to do first before I do this

I currently have my fan ON all the time with a single speed motor. With the one month cold snap it helps with circulation and evening out heat between levels and as well as humidity. But Im scared to see my next electrical bill

To me I have the most non HE furnace out there. Its HE, but a single speed motor and not dual stage. Kind of an oxymoron on HE, but whatever

I have never replaced a furnace all these years of home ownership. What is the average cost? While putting in the motor is an idea, I could just put that money into a new furnace that has one already and dual stage. But that would the last resort kind of thing
New furnace is about $3-6k depending on brand and efficiency.

The only reason I haven't upgraded to ECM fan in my new place is that I'd like to replace my 0.80 EF furnace, .67 EF water heater and add an HRV all at once and with a nice rebate.
Probably won't happen any time soon with our current provincial administration.

I run my old AC blower 20min every hour all day. My biggest gripe with it is good noisy it is when running. I should see if I can show it down when on fan only.

I had a nice new high EF furnace installed at my old place for about $3k with rebates. It was so quiet.
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Jul 21, 2017
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TomLafinsky wrote: I run my blower motor 24hr/day, 365days/year. You literally don't hear anything. I do it to maintain a uniform temp throughout the house.
+1 on this. Also prevents the basement from getting that musty smell.
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I have a Carrier programmable thermostat that can be set for variable speed fans (looks like it still uses the one G wire and I am not sure if it just sends a voltage) as well as variable speed compressor/two-stage furnace (not that I have any of these). The super comfort setting uses the fan all the time at low speed when outdoor temp is -11 to +4C (I have an outdoor temp sensor).

Looking at this
https://www.genteqmotors.com/Products/A ... _IM_Motor/
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TomLafinsky wrote: I have no idea if what you want to do will work flawlessly as I have never hacked a furnace. Maybe someone else will be able to confirm. I can tell you that my stat is a Lennox SignatureStat. Google "lennox signaturestat" and you can read the owner's manual if you wish. I also have an outdoor temp sensor. But contrary to you, I can run the blower at minimal speed to move the air irrespective of the outdoor temp. This is an old stat, no wifi and fine with me. Even has battery backup so no need to reprogram if I lose power for a few hours.
The air handler will tell the motor and me what to do, if I can find a manual. The Genteq motor has a wiring guide as to how much voltage it receives to determine whether it runs at full or half speed. I imagine the thermostat sends a signal to the control board of the air handler which in turn sends a voltage signal to the ECM. So I guess I will have to see if the air handler can send full or half speed signals. Can't change speed as only the thermostat can send a signal for that.

I can turn off power to the heat pump for weeks or months all summer (don't need to cool/dehumidify very much where I am) and it retains memory.
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engineered wrote: New furnace is about $3-6k depending on brand and efficiency.

The only reason I haven't upgraded to ECM fan in my new place is that I'd like to replace my 0.80 EF furnace, .67 EF water heater and add an HRV all at once and with a nice rebate.
Probably won't happen any time soon with our current provincial administration.

I run my old AC blower 20min every hour all day. My biggest gripe with it is good noisy it is when running. I should see if I can show it down when on fan only.

I had a nice new high EF furnace installed at my old place for about $3k with rebates. It was so quiet.
Ill be installing some programabble thermostats soon. I have an Ecobee with sensors brand new, so will probably set it up to cycle like that. Right not I just have digital ones, and its a pain. But busy unpacking and setting up a programmable thermostat is low priority
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Feb 9, 2006
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@thriftshopper

There's some misinformation in this thread and I'll ask you to ignore the noise and the random ramblings.

I've done the conversion, you don't need to have a special Thermostat or anything.

Google the Azure digimotor. Or take a look Here

The motor will use ~50% the power of your old PCM motor (500W vs 800W), it won't need a start capacitor, it has a nice slow ramp up so no huge surge.
The Digimotor has a 50W super low RPM full time circ mode, which is great to just moving air, keeping temps even and for helping filter air if you have a EAC or a nice large 5" filter box.

The new motor is super quiet even when it's spins at the same or higher speeds than the old motor. The 50W circ mode is almost completely silent unless you're right next to the furnace.

My experience. The Change over is super easy, the Azure digimotor does autosizing so you don't have to worry about getting the speed taps right and adjusting it. Just get the motor that comes closest to your current rating. The Digimotor comes in 0.5 and 1HP ratings. If you have a 3/4HP get the 1HP and it'll size down during the autosizing setup. You just take note of where your old motor connects up on the control board and then transfer those connections points over to the new motor and you're done.

The hardest part will be figuring how to get your blower cage out and taking out the old motor and swapping it in. In 90% of furnaces they use a belly band in the odd chance it doesn't you may need to find a separate mount.

I've researched the Genteq motor as well, it's actually a little more complicated to setup than the Azure since the Azure since V2 now just uses regular 120V taps vs 24V taps like the V1. The Genteq also doesn't autosize. IIRC the Genteq was more to replace the Constant torque PCM motors but also works to replace regular PCM motors.
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TomLafinsky wrote: I had totally forgotten that although I never 'hacked' a furnace, I did 'experiment' about 10 years ago.

You see, at the time replacing the blower motor with an OEM part was around $1,500. So I decided to explore the possibility of buying a motor on the used market. And I did. It was the same Regal Benoit ECM 1 HP motor, but what I didn't know when I bought it is that it came from a Goodman furnace. My furnace is Lennox.

The fact is although one might be able to buy an (almost) identical motor, each motor is programmed differently. And this is where it can be very dangerous. It just happens that the motor I had purchased was programmed to run at a lower speed. It didn't matter if it was first stage, second stage or just to move the air. It was always running less fast and therefore producing less airflow.

I guess you can imagine the danger. Right after I installed it I started the furnace and even at the first stage the air coming out of the register was BURNING HOT. I immediately stopped the furnace. Only if I was using the second stage then the temp of the air was more acceptable, but it was still hotter than it was supposed to be.

All this to say that I don't think it is wise to try converting a standard furnace to a variable speed one.
It's perfectly safe to replace the motor, but you have to setup the new motor to run at the correct speed. The Mars Azure unit has a self learning function so you can teach it the correct speeds.

Also, fyi, here's an older thread on ECM motors.
https://forums.redflagdeals.com/ecm-mot ... s-2036127/
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Jul 11, 2017
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All this to save $7/month in electricity! I don't get it?
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Bella125 wrote: All this to save $7/month in electricity! I don't get it?
You really don't.

Considering the motor costs <$300 all in

Saving $7 (you actually save more for those running the fan 24/7) a month is $84 a year
You break even and start coming out a head A little after the start of year 3.

Not to mention you now have the comfort benefit of more even temps from air being circulated around the house.

The slow ramp up and the lower energy foot print also has benefits to those who maybe off grid or Want to extend their generator runtimes.
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Bella125 wrote: All this to save $7/month in electricity! I don't get it?
Probably even more if you run it continuously for comfort and to clean the air. It's also much quieter which is also nice benefit.
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Vaughan
Is changing AC to ECM motor straight forward or you need an adapter with added cost ? Something to ponder.
thriftshopper wrote: I spoke to the sales rep of a local (and reputedly very reputable) HVAC dealer and service company who told me not to bother replacing the HP until it goes.

Since the HP and air handler may have another 5-10 years of life left, if not more (he used to install 80% Carrier back in the era when my current house was built and thinks it should last another 5-10+ years - circuit boards re what goes these days).

I've heard that savings from converting the motor from AC to ECM can be significant. Just wondering where and how to start? Size of the motor and mounts, and voltage as a start?

TIA
Certified HVAC Pro. Committed to Customer, not brand. Past RFD Review
2024 AC, Furnace, Heat Pump and Water Heater Groupbuy
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TomLafinsky wrote: You don't buy a variable-speed furnace in order to save a few bucks on electricity or NG. You buy one because you want a higher quality of life.

I had to spend an additional $2.5K to get a variable speed furnace instead of a 'regular' one. A variable speed furnace is so quiet. The blower motor is running 24/7. The temp throughout the house is a great deal more uniform and life inside the house is more enjoyable. And it does remove more dust from the air if you have decent filter.

I have heard that running a variable speed furnace at the lowest speed during heating season is supposed to translate into a saving on NG, but I do not know if it is true and I never investigated it. Nevertheless I only run the furnace at the lowest speed during heating season because I like it quiet.

Though when using the furnace with A/C you can't run it at the lowest speed. It automatically goes to second stage.
Im going to wait to replace my furnace instead of doing this. If the payback is 3-4 years on it, then save my time and money now and spend it later
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newlyborn wrote: Is changing AC to ECM motor straight forward or you need an adapter with added cost ? Something to ponder.
It's not plug 'n play but doesn't seem too complicated. I will have to look at the air handler and what the existing motor and wiring looks like first.
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newlyborn wrote: Is changing AC to ECM motor straight forward or you need an adapter with added cost ? Something to ponder.
thriftshopper wrote: It's not plug 'n play but doesn't seem too complicated. I will have to look at the air handler and what the existing motor and wiring looks like first.
It actually is plug and play for the most part.

Just a tiny bit of homework to confirm if your existing mount is compatible or if you need to order a mount.
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tebore wrote: It actually is plug and play for the most part.

Just a tiny bit of homework to confirm if your existing mount is compatible or if you need to order a mount.
Well, it is a not straight swap out, like changing a CPU or mem sticks (or chips). Heck, even the relayed hard start capacitor I put on the HP compressor wasn't really PnP (still had to fidn the right terminals on the actuator and capacitor).
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Deal Guru
Feb 9, 2006
13377 posts
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Brampton
thriftshopper wrote: Well, it is a not straight swap out, like changing a CPU or mem sticks (or chips). Heck, even the relayed hard start capacitor I put on the HP compressor wasn't really PnP (still had to fidn the right terminals on the actuator and capacitor).
Have you seen this yet?


The video is ~8 min long. Honestly that's how long it takes to wire up. The other 30-40 mins will be spent on physically taking the old motor and blower out and cleaning everything while you have it out.

I'm not arguing because I know not everyone has the same hands on skill. Just wanted to point out it's fairly straightforward.
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Jul 11, 2017
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TomLafinsky wrote: You don't buy a variable-speed furnace in order to save a few bucks on electricity or NG. You buy one because you want a higher quality of life.

I had to spend an additional $2.5K to get a variable speed furnace instead of a 'regular' one. A variable speed furnace is so quiet. The blower motor is running 24/7. The temp throughout the house is a great deal more uniform and life inside the house is more enjoyable. And it does remove more dust from the air if you have decent filter.

I have heard that running a variable speed furnace at the lowest speed during heating season is supposed to translate into a saving on NG, but I do not know if it is true and I never investigated it. Nevertheless I only run the furnace at the lowest speed during heating season because I like it quiet.

Though when using the furnace with A/C you can't run it at the lowest speed. It automatically goes to second stage.
Last home was a 1400sqft bungalow with variable speed furnace, average electric bill $180 month. This house 2000sqft with mid efficiency furnace, average electricity $150 month. I notice no difference in comfort or air quality between running fan constantly compared to now with the Ecobee it runs 10 minutes per hour. By the way, you got ripped off, the difference between my variable speed and the 2 stage was about $400!

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