My biggest noise problem is noise from a HRV system

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We have a HRV (heat Recovery Ventilator) in the house and it generates an incredible amount of RF emissions from low to high frequency spectrums. The emissions are so strong that the entire house wiring is radiating this noise. I have raised the issue with the manufacturer but have not received to date a satisfactory reply. I want to reduce the noise by about 50 db. The first response from customer service was to put a power line filter on the radio. Not! This has to be stopped right at the HRV. I have done some research into commercial power filters for EMI reduction, but I am frustrated by their lack of a statement as to what the reduction of unwanted emissions is.

Does anyone have a similar experience with an HRV, and if so, how did you resolve it? 
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David Ramer, VE7YA

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Posted 4 years ago

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Steve K9ZW, Elmer

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Hi David - can you give some details - what type/brand HRV, wiring (plug in or mains, voltage/draw/phase)...

Curious what you think the source and emitter in the HRV is?




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Lewis Cheek

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David, I have no knowledge about HRV, however folks next door have a Samsung Plasma TV and that thing is all over the hf band. About s6-s9 most places and I have found a MFJ 1026 works well if connected to a outside receiving antenna.
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George Molnar, KF2T, Elmer

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Have not worked with those units, but suggest aggressive power and control line filtering at the unit, ensuring electrical continuity and shielding throughout the unit, and an effective RF ground. Sounds like a toughie. Can the thing be enclosed in a screen somehow?
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Walt - KZ1F

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Hi David,
   We have a Venmar ERV hooked into the Waterfurnace and it has zero emissions. But as Steve asked, what make, model, and when was it installed? Sounds like a wiring issue or bad fan. Did it just start or has it been present since installation?

Walt - kz1f
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KY6LA - Howard, Elmer

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While I have had no experience with an HRV, I have had a lot of experience killing RF noise sources,

Your absolutely correct. A line filter at your radio won't fix it. You need to kill it at. The source.

First, you need to figure out exactly where the noise is coming from. RF sniffers really help here

It usually is sourced through a power lead or faulty grounding of the equipment. If the device is in a metal cage, sometime just grounding the case , cleaning off rust and paint, can lead to significant reductions .

Next Toroids, Toroids, Toroids. I find that big 2-1/2" clamp on Toroids ($12) can fix most issues or a least tell you if you are on the right track
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David Ramer, VE7YA

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The manufacturer is Imperial Group. Website is
The HRV is a model SS 3.12 DD (TP). Power is 120 VAC @ 1.5A single phase.
The unit is constructed in a large metal box with 4 ports for air on the top. The unit plugs into a standard three conductor socket. It also has a remote control cable that goes to the two bathrooms for increasing the air flow. The unit was installed this last summer and is on warranty, so I do not wish to open it up. I suspect the noise is generated by a fan motor. I knew I had a serious noise problem some months ago, but didn't track it down until I was able to sniff around with a handheld receiver (Icom IC-R20). I have placed four 31 material snap-on ferrite cores on both the power cable and the control cable with little detectable reduction.
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Stan - VA7NF

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Looking at the Imperial SS 3.12 there are several observations.

It is a metal case but the door is a large service panel that, normal for HRV, is a lift off.  That offers no EMI protection.

Often these HRV boxes use foil insulated ducts.  I see the adapter is plastic - Check if the foil is insulated from the box.  It could be a major antenna.

It has two variable, medium power fans.  That means there is a small VFD supplying power to those fans, and VFD (Variable Frequency Drives) are known for EMI (A switching supply on steroids without any noise suppression.)

Since it is under warranty and you have a great spectrum display: Take a screen shot of the noise, write a brief description, and contact your service department.  Request they install an EMI filter INSIDE the case with at least 60db suppression in the broadcast band and above.  If you can record a noise sample in the BCB showing the interference it will help.  Head Office design people are often more sensitive to BCB interference than exotic ham interference.

I was "lucky" with my VFD as it wiped out the local airport landing beacon.

Stan VA7NF 

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David Ramer, VE7YA

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Thank you for the great suggestions.
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Scott AC8DE

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I read the specs on your unit.  Stan VA7NF hit the nail on the head.  When I installed a new high efficiency HVAC last year, I stopped just short of the units with VFD's and went with a 2-speed unit.  The difference in efficiency is only a few percent, so the cost savings difference isn't enough to talk about.  I knew the problem with VFD's and ham radio... and now you do too.  A tough way to find out.

Perhaps asking the company to swap out to a unit that has a fixed speed (or 2-speed) would be the simplest solution.  VFD's are always a problem around radio equipment.  Sure, you can work on filtering it, but that is a big hassle.  HVAC companies are usually not equipped to understand and fix such technical issues and I'm guessing, you'll end up on your own if you want it done correctly.  That's the cynic in me talking.

If you can't get the company to fix it for you... If it won't hurt anything to do so, just shut off the recovery system while operating.  Is the amount of heat you are losing during operation of your shack a big deal?  I'm guessing not.

I don't know what your call sign is (as you didn't publish it here), but where do you live in terms of geography?  A HRV system is something that has little real payback unless you live pretty far north if you have a modern HVAC system.
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David Ramer, VE7YA

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Thank you for the comment. Call sign is VE7YA. Location is Victoria, BC, at the southern end of Vancouver Island. I am not worried about heat loss. The HRV was installed to resolve air quality and mold problems in the house. Yes, I could just turn it off when operating, but that lets the manufacturer off the hook. There are all kinds of noise problems around. I believe that we the ham community have to start making more noise about noise, and making manufacturers take a more responsible role in the design of their products, and the government has to step up its role in ensuring products meet guidelines for unwanted emissions. Otherwise, as time goes on, it just gets worse.