eHam Forums => RFI / EMI => Topic started by: KD3C on December 12, 2012, 10:52:01 AM

Title: Lennox HVAC EMI-RFI
Post by: KD3C on December 12, 2012, 10:52:01 AM
Just prior to getting back on the air, I had a "top-of-the-line" Lennox HVAC system installed in my home.  I hooked up my rig and immediately enjoyed 10-20db over S9 QRN which came and went as if someone threw a switch.  It didn't take long to associated that with the cycling of the HVAC.  Rather than start at ground zero with Lennox, has anyone out there experienced the same with Lennox units specifically and if so, has anyone been successful in getting resolution i.e filter kits etc.? I'm sure I am not the first Lennox (ham) customer with this problem.

Title: RE: Lennox HVAC EMI-RFI
Post by: NK7Z on December 12, 2012, 11:43:24 AM
Rather than start at ground zero with Lennox...


I had a slight RFI issue with a new heater install.  The installers contacted the vendor, and they had a fix they sent out to the installers for free.  RFI gone...  That said, I had built into the contract, that if the heater generated RFI the vendor would correct, or remove and re-install the old heater.  The issue was a variable speed fan.  I believe the fan is controlled by a variable duty cycle  power supply.  The fix was a choke on the power lines for the fan...  Try running the fan to full speed and see if the speed changes the character of the RFI.


Title: RE: Lennox HVAC EMI-RFI
Post by: WB4BYQ on December 12, 2012, 02:07:31 PM
The January 2013 issue of QST has article listed under Hinks and Kints how another ham fixed his RFI from a variable speed motor unit.


Title: RE: Lennox HVAC EMI-RFI
Post by: AB9SW on December 13, 2012, 05:26:17 AM
I had a similar problem with a recently installed Lennox heat pump system. I initially thought the variable frequency drive on the air handler was the source of the EMI. After installing AC line filtering on the blower motor and additional filtering on the AC input to the air handler I got the noise down to S6 on my HF radio, better but not good enough. Using a AM broadcast radio I tracked another noise source to the Lennox setback thermostat wiring. I installed ferrite common mode chokes on all the cables to the thermostat and was able to get the noise on my HF radio down to S0 to S1 on all bands while the heating system was running.   

Title: RE: Lennox HVAC EMI-RFI
Post by: K0YQ on January 08, 2013, 10:31:41 AM
I'm looking to put in a new furnace in the next few months to beat the new May 1 venting regs.  If anyone has any specific feedback on units that do or do not produce RFI I'd sure appreciate the feedback.  Also the idea to put the RFI verbiage in the agreement is a great idea.  Thanks all.

Title: RE: Lennox HVAC EMI-RFI
Post by: WB4SPT on January 08, 2013, 11:45:09 AM
Two homes with two different Trane multi-speed air handlers in the 3 to 4 ton range.  No issues seen on 80 to 15m. 

Title: RE: Lennox HVAC EMI-RFI
Post by: K9CPE on January 29, 2013, 11:15:12 AM
I have a Lennox system installed and have exactly the same problem. The issue is not the variable speed fan but the heater induction motor - when the burners light up the furnace produces 9+10-40db from 1.8 through to 18 MHz. Another ham in my club also has the same issue with the same furnace (I think I see a trend here).

Lennox is aware of this issue and have RFI suppression kits ( some include new control boards) for their furnaces.

The installers came out before Christmas to install an RFI suppression kit (which did not include a new control board)  provided by Lennox which made absolutely no difference whatsoever. I am waiting to hear back from Lennox and this morning left a message for the tech to contact me with an update. I will keep you informed on what happens.



Title: RE: Lennox HVAC EMI-RFI
Post by: FLIGHTDECKCA on February 25, 2013, 11:53:43 AM
After installing AC line filtering on the blower motor and additional filtering on the AC input to the air handler I got the noise down to S6 on my HF radio, better but not good enough.

Hello all, I'm new here, and confess that I'm not a ham operator.  I found this thread by searching about EMI/RFI problems caused on my home computing network by a new furnace motor.  It seems that interference from these new ECM motors is a relatively common occurrence, and that ham operators are most susceptible.  I can at least say I share your pain!  I'm hoping we also share solutions to the problem, which is why I've joined the network here.

AB9SW mentions installing line filters on the AC lines to the motor, and I've seen this mentioned by others as well.  I think this is where I need to start in my case, and am looking for a little assistance learning how to select the correct components, since I'm not an electrical guy.  But if you use small words and speak slowly, my old courses might start coming back to me  ;)

I've isolated the problem to the new ECM fan motor I installed in an old electric furnace last week.  When it turns on/off/changes speeds, my network traffic stops dead (for example, continuous pings suddenly become lost packets).  When it resumes, the traffic moves again but I see a lot of scatter in ping times (latency). 

Unfortunately a portion of my network relies on "powerline ethernet" (homeplug) technology, which uses the household AC wiring to carry the network signal.  This is being used to get the internet connection from the 3.5 GHz radio receiver on my garage to my house about 100 ft away.  Through testing I've determined that this is the only link in my network that is being (noticeably) affected by the motor.  It's my conclusion then that the motor is injecting unwanted EMI noise back onto the household AC wiring that the homeplug system uses as a carrier, thereby disrupting it.  Since all the Cat5e wired network in the house appears to be immune, it is also my conclusion that my network is not being affected by RFI from either the household AC wiring or the low-voltage thermostat wiring.  That's my rationale then for focussing on filtering the AC input to the motor.

The motor has two high-voltage AC connections.  The power connection is ~230 VAC, two wires connected to L1 and L2 of the AC wiring to the furnace.  The on/off signal connection is 115 VAC, one wire connected to the fan relay on the furnace, which is ultimately connected to L1.  (The remaining wires are the 24 VAC thermostat harness, which I'm ignoring as mentioned.)

Through searches here and elsewhere, again mostly ham sites, I learned that an "EMI powerline filter" might help, and that Corcom makes them.  I've read up on their products, found a dealer, etc., and am now just trying to select an appropriate filter from their catalogue.  I'm using their selector chart here: (

I get stuck at the question "For switched mode power supply?".  I don't know if that's intended for building an SMPS and preventing it from polluting the AC-in, or if instead it's just referring to any device that may have similar noise characteristics like those of an SMPS (high-frequency switching).  My understanding is that the ECM motors contain a rectifier and inverter, with the inverter possibly controlling the motor by pulse width modulation (PWM), and thereby behaving like an SMPS.  (All this is from wikipedia btw, so please correct me if it's totally out to lunch!  :) )  I don't know whether I should treat the all-in-one ECM motor as an SMPS or not when selecting a filter.  Any recommendations?

The next decision is the current rating.  The motor's stated full load amperage (FLA) is 4 amps.  I don't know what the 115 VAC signal line draws.  I'm not sure how much above the rating I should select a filter.  For example, some of the Corcoms are available in 5 and 10 A ratings.  Is 5 A cutting it too close?  Any guidance / rules-of-thumb on selecting a current rating?  I don't mind the filter being a sacrificial fuse compared with the $400 motor, but I don't want to be cooking them unnecessarily.

There is a choice between low leakage current and not.  I'm assuming this is not really a concern for a furnace motor.  Agreed?

The rest has to do with the application, for example:
    B-series:  "Suitable for high impedance loads"
    R-series:  "Well suited for low impedance loads where noisy RFI environments are present"
Everything is relative, so where does an ECM furnace motor fall in the realm of low/high impedance loads?  The R-series are supposed to be a more effective filter, but is an ECM motor too much to be considered "low impedance"?

So, if anyone could provide some guidance on the SMPS decision, the current rating, and whether I need worry about the leakage rating, that would be greatly appreciated.  As you can see I'm as much interested in learning as getting "the answer", however if you're keen to put me (and this thread) out of misery, exact part numbers are also accepted  ;)

Thanks so much!  :)

Title: RE: Lennox HVAC EMI-RFI
Post by: KD0REQ on February 26, 2013, 11:30:11 AM
I would say that a VSD motor (variable speed drive) controller, or any other electronically switched motor, is going to show a low impedance, as there is no capacitive coupling to the power line from the switching devices.

whatever, some basic techniques are going to work a significant part of the time in EFI control.

(1) shield everything that can be... PC boards, inter-system wiring, etc.  return shields to frame ground, and make sure the bare or green ground wire (brown in British countries, varies in others) is firmly bound to the metal frame from incoming power.  insulate the inside.  if there are heatsinks, use perforated metal for the shield to let some heat out.

(2) the stuff you can't shield, filter.  a low-frequency ferrite toroid core is a good start, generate common-mode noise filtering by wrapping as much of all the wiring off a specific section of the system that you can around the toroid, and lightly twist-tie it in place.  space as evenly around the core as you can.

(3) the stuff you can't filter, bypass.  for 120/240 volt service and below, "Y" series safety capacitors across power lines, and "X" series from most control-type wiring to ground.  it may be necessary to get some contractor splice boxes (common sizes are 4x4x4 or 6x6x6 inches, one or both ends removeable, the rest have knockouts) and mount them outside the system to house a Corcom type filter.  in the case of a furnace, use a close nipple and locknuts to hold the box to the furnace where the power used to come in, run the furnace leads to the LOAD of the corcom, hook the power line to the LINE side.  had ground to the box with locknuts, and wires from there to the furnace frame and the corcom, as well as the power input.  all the connections to the same screw with locknuts for a low-impedance common ground.

(4) install any manufacturer noise kits if availiable, but don't wait for them, try what you can without hacking the system up and voiding the warranty.

Title: RE: Lennox HVAC EMI-RFI
Post by: FLIGHTDECKCA on February 26, 2013, 05:03:12 PM

Thanks Scott, a lot of great info in there.  I think though that quite a bit of it focusses on preventing emission of RFI off the motor and surrounding wiring.  In my case, I believe (hope) that the issue is more of EMI being injected directly back into the household AC wiring and conducted to my homeplug comms network.  So rather than start with a broad approach of trying to shield everything that's there for RFI, I'm starting with just the EMI line filter on the AC leads to the motor, and hoping that does the trick.  If not, honestly I may very well be pitching the homeplug network and my 3.5 GHz internet service altogether---it's been a thorn in my side for far too long---and moving to 4G now that it's available in my area (and LTE is not far behind it).

I came to the same conclusion this morning, that the motor would be considered "low impedance", although my reason is probably less scientific!  :)  I found some info on Corcom's website that they consider household AC wiring as "low impedance" with about ~50 ohm (ref: (  (I realize that's oversimplifed, but it works for me.)  I swag the motor's values at that or less and therefore was happy to consider it "low impedance" as well (treating is as a purely resistive load and ignoring any reactance components, again maybe oversimplified). 

In any case, I needed to make a selection quickly, so I already placed an order this morning for some Corcoms.  I hedged my bets and bought EMI filters for both a "low impedance" load and for a "high impedance" load: 
5VR1 ("low impedance" load) (
5VK1 ("high impedance" load) (

I selected a 5 amp size based largely on what was available in stock (the 10 amp size were backordered). 

For leakage current, I found some info on their website that higher leakage current is actually a good thing as far as filter effectiveness is concerned (ref: (  Since the "low leakage" models were also not in immediate stock, I happily ordered the "standard leakage" ones. 

The other question I struggled with was the SMPS question.  After reading up more, I learned that the "EN 550xx (CISPR) Class A / B" mentioned in the CORCOM selection chart are standards for EMI.  For example EN 55014-1 is a standard for EMI emissions from household appliances, power tools, etc.  The CORCOM filters in that side of the chart seem to correspond most to digital equipment, particularly IT eqpt, but in any case are there to help mfrs produce products with SMPS that will meet those standards.  In my case I'm not after standards compliance---that burden was on GE when they produced the motor---I'm simply trying to crunch EMI with whatever I can get.  Since ready stock included only the general application filters anyhow and none of the ones intended for a SMPS, it was a quick decision.

I also decided to try a filter only on the 240 VAC power leads to the motor, and not on the 115 VAC signal lead as well.  I may yet need to do the latter, but I'm gambling it's not be needed based on the wiring configuration.  It's the 240 VAC leads that provide the power for the motor and controller, not the 115 VAC signal wire, so I'm thinking the interference from the inverter is more likely coupled with the 240 VAC power leads rather than the signal wire.  I could be wrong of course, but this is someplace to start.  If it doesn't work I can try adding a filter to the signal wire as well.

The filters should arrive tomorrow, so I can spend the approaching snowstorm playing in the wiring of my furnace, yay  :)  I'll post back with the results.

Oh, the toroid winding thinger that you mention, from what I've seen of photos of the insides of similar motors, there is already one or two inside.  Doesn't seem to be enough in my case, so I'm hoping the Corcoms do it.  If I ended up needing to filter the low voltage thermostat wiring (don't believe it's needed here though), I read recommendations like yours to put a wound doughtnut on them.  Also something called a "ferrite bead"?  Anyhow again, hoping I don't need to touch the thermostat wiring.

Many thanks  :)

Title: RE: Lennox HVAC EMI-RFI
Post by: WB4BYQ on February 26, 2013, 05:48:51 PM
Please keep us informed of the progress.



Title: RE: Lennox HVAC EMI-RFI
Post by: KB4QAA on February 27, 2013, 07:27:56 AM
Many of the HVAC manufacturers produce units that have terrible RFI.  They chose to save money by not including any filtering.  If a new owner complains then they typically provide the filter kit at no cost.   

Call your installer and give them holy heck.

Title: RE: Lennox HVAC EMI-RFI
Post by: FLIGHTDECKCA on February 27, 2013, 08:31:09 AM

Hi Bill, this was a self-install.  It was not a new furnace, just a blower motor replacement that was originally part of an old electric furnace.  The furnace is fine (pretty hard to kill an electric furnace), it's just the old AC motor that was dying.  The ECM motor I installed is sold as a direct drop-in replacement for generic AC blower motors (it's a Genteq Evergreen IM, (  Everything is onboard the motor, there are no external control boards, etc., like is sometimes the case for a complete new combustion furnace.

I've contacted the motor manufacturer, GE, a couple times and have not received any response at all.  In any case I suspect their position will be "it was FCC Class B certified" and you probably already know what that is worth.  This is reflected in their support info for a separate yet similar motor design here: (  Note that information suggests adding filters onto the thermostat wires, but nothing about the high-voltage AC power leads.

The retailer where I purchased the motor has not been able to provide any useful info about EMI filters for this motor, or kits available from the OEM. 

It may very well be that the motor is fully FCC compliant.  Since my issue is with a homeplug ethernet-over-powerline network, and I've heard those can be susceptible to this sort of thing, the "fault" may very well be with a network design concept that tries to operate on a wiring system that is simply not intended for that purpose, and potentially "hostile" as far as interference is concerned.  I believe my homeplug devices are older models and the newer specs may very well have improved filtering/tolerance to other things on the AC wiring like ECM motors. 

Still waiting the the Fedex truck with my filters...  :)

Title: RE: Lennox HVAC EMI-RFI
Post by: FLIGHTDECKCA on February 27, 2013, 04:51:22 PM

Success!!   ;D  At least by my lowly standards  ;)  The 5VK1, the filter best suited for "high impedance" loads, ended up being the most effective. 

I started with the other one, the 5VR1 for "low impedance" loads.  It certainly reduced the network disruption when the furnace motor was doing it's thing, but there were still packet losses, particularly on motor start/stop, and quite a bit of latency scatter (erratic ping times).  Better, but still not great.

I then tried the 5VK1, not expected it to be better, but it's very good.  Not a single lost packet in 25 mins of motor switch testing, and only very limited effect on ping times when the motor was switching on/off.  When the motor changes speeds there is virtually zero effect on ping times.  Since my system is set for continuous run for air circulation/ventilation (and thus the reason I upgraded to the low-power ECM motor in the first place), then on/off switching is not really a concern anyway.  I suspect if I were to put a filter on the 115 VAC signal wire as well, which is the one controlling the on/off switching, that even the slight interference during on/off switching would go away too. 

One of the higher performance filters intended for SMPS applications might also deliver better results. 

For now I'll monitor it and apply the not-broke-don't-fix philosophy.  It's maybe not a complete solution, but certainly enough that I've remedied the network disruption and can now surf the net again with impunity.  Why it's almost as if my internet connection and home heating system are no longer related, Gasp!  ;)  It's going to take me a while to kick the Pavlovian response I developed this week of turning off the furnace to check email...  :)

If I were to go ahead and also filter the 115 VAC signal wire, I'm a little unsure of what to connect.  It's only a single wire, but the Corcom filter uses two.  My uneducated guess is that AC neutral should be the second wire.  Neutral from the AC mains is already connected to the furnace chassis as a ground.  It seems then that the second connection on the Corcom would simply go straight to ground as well.  Does that make sense?

Thanks all for the support!  :)

Title: RE: Lennox HVAC EMI-RFI
Post by: K3GAU on February 28, 2013, 11:02:18 AM
GA All,

I have a bit of a different RFI problem with my Trane furnace.  It is one of the high efficiency units and we also had an electronic air cleaner installed with it.  Everything seems quite with the blower and electronic air cleaner running. Our noise starts when the furnace actually fires the burner.  I can hear some noise on 40 meters and it gets louder as your go up in frequency at least up through 10 meters.

I have installed a commercial EMI/RFI filter on the AC line going into the furnace, I have added RFI cores on various power supply lines (going to the blower, ignitor, etc and it has seemed to help but I still have several S units of noise on several of my upper HF bands.  Any thoughts on what it might be and what it might take to get completely rig of it?

Dave K3GAU

Title: RE: Lennox HVAC EMI-RFI
Post by: QRP4U2 on February 28, 2013, 03:04:36 PM
Check ot this discussion as well:

Phil - AC0OB

Title: RE: Lennox HVAC EMI-RFI
Post by: VE3EDY on May 24, 2013, 02:07:07 PM
EMI Eliminated 100 %.

Please see  the article I wrote  in 2013 January Issue of QST.

Technical Correspondence :

Heating Ventalation Air Conditioning (HVAC) EMI Generation.

Title: RE: Lennox HVAC EMI-RFI
Post by: K3LRH on February 05, 2014, 09:13:19 AM
.........I have the same problem with a YORK AFFINITY heat pump.  S9+20 on 20M, 17M and less on other bands.  The RFI  seems to be coming from the OUTSIDE FAN unit.  Currently, the supplier is in contact with YORK.  Of course, they have "never seen anything like this before" with the YORK AFFINITY units.  The tech guy said that the fan motor is an ECM type, so we'll see what happens.  I posted this in case other ops have had issues with their YORK units. I suspect that the motors are probably of GE origin.  Update will follow.


Title: RE: Lennox HVAC EMI-RFI
Post by: WB4SPT on February 09, 2014, 06:16:57 PM
Correction to my previous post, I did have harmful emissions from my Trane furnace with the variable speed induction motor on 20meters on the heat cycle.  I ended up putting a bead on each of the phases of the induction motor, AT the PCB area.  You do need to pull the three contacts out of the molex like connector to accomplish this.  Each bead took 2 turns of motor wire, and the results are great.  Further work of using a corcom at the AC inlet and beads on the thermostat wiring did little else.  It was key to attack the noise source close to the PCB, before the motor wires radiate to other wires.  I also pulled the motor wires out of the bundling, braided them together and made an effort to keep them away from other wiring.  It worked.

Title: RE: Lennox HVAC EMI-RFI
Post by: KD0REQ on February 10, 2014, 10:04:44 AM
a split bead over that entire harness at the PCB might have done it, too.  ten bucks a unit to thoroughly suppress these control boards at the factory, and nobody does it...

Title: RE: Lennox HVAC EMI-RFI
Post by: WD9DMP on March 16, 2014, 09:59:34 AM
Regarding the interference issue from furnace air handlers' ECM motors, I recently solved a similar issue.

I installed a GE Evergreen IM ECM retrofit motor in my older furnace for reduction of motor noise and more efficient constant-on fan operation. It works great for that application.

However, I found that there was some interference being generated to a VLF (5KHz - 50 KHZ) lightning detection system I have installed. I installed common-mode ferrite chokes on the thermostat wiring and motor power leads, but the EMI persisted.

The problem turned out to be harmonic distortion being introduced into the AC power lines. This is caused by the non-sinusoidal current draw by the ECM motor. The DC power supply of the motor pulls power from the AC line in two sets of pulses at each AC peak, rather than in a smooth sinusoidal manner, as with a conventional PSC motor. The current bursts were causing EM spikes to be radiated by the power line and picked up by the ferrite antennas of the system.

GE send me a very large choke to put in line with the motor hot lead. This smoothed out the current pulses and essentially cured the issue.

See this really great white paper on ECM motor harmonic distortion:

I also put together a report with pictures for GE in exchange for the free choke.



Title: RE: Lennox HVAC EMI-RFI
Post by: WD9DMP on March 17, 2014, 06:04:02 AM
I took some additional oscilloscope measurements that verified the effectiveness of the choke in attenuating the noise. New link:


Title: RE: Lennox HVAC EMI-RFI
Post by: KD0REQ on March 18, 2014, 05:31:31 PM
Xerox had that issue with copiers in the 70s.  put a lot of EMI on the power line in the commercial building my first employer had a radio production studio in.  on request, the Xerox rep would come out and put a big old choke in the power line, solved the problem.

one of the TV engineers had a continuing issue with a big old TT70 2-inch quad VTR in the studio.  when it started recording badly, took him a week to find out it was throwing huge spikes into the line because the 50,000 uF filter capacitors in the power supply were dry.  the motors were servomotors, gen-1 huge things, driven by pulses.  he went through every spare board in the place, plus all the working ones in the main studio down in Fargo, before he finally put the scope on the power supply.  he even asked me, the lowly news guy, what I thought it looked like.

Title: RE: Lennox HVAC EMI-RFI
Post by: VE3HUT on April 04, 2014, 01:29:27 PM
Lennox has an EMI Filter Kit (Part # 604552-01) which can be obtained through a Lennox certified HVAC installer.  The kit consists of an EMI FIlter and two ferrites.  The filter goes in between the supply voltage and the IFC control board.  The ferrites are installed on the thermostat wire and on the input wire from the supply junction box.

Call Lennox and tell them that this kit does the trick!


Title: RE: Lennox HVAC EMI-RFI
Post by: N2FKW on April 15, 2014, 10:23:20 AM
As others have noted this is a known problem with newer high efficiency Lennox furnaces. In my case I also noticed the correlation between the Furnace running and the terrible RFI. At first I thought that it might be the variable speed DC motor driving the blower. Further investigation (listening with a handheld AM portable radio while the furnace went through its cycle) revealed that the real culprit was the variable speed DC motor driving the "inducer" which brings in combustion air from outdoors. After consulting with the dealer which installed the unit and waiting for a few weeks, a Lennox factory engineer showed up at my house with both a "filtering kit" (ferrite beads and a AC line filter) plus a new controller board for the furnace. After a few hours the install was done and the RFI was completely gone - all at no cost to me.

Now my only "local" RFI problems are confined to faulty sodium vapor street lights that cycle on and off through the night. Finding them requires driving/walking around and noticing the cycling lights with both your eyes and and with the handheld AM portable radio. Note the pole number(s) and location of the offender and report them to your local electric utility (via phone or website). I've had good luck with my utility (National Grid) replacing the faulty units in just a few days.

73s from N2FKW