I just had a successful outcome with RFI from a new Lennox furnace we
installed 3 weeks ago. It is a Lennox SLP99UHV gas furnace.
When running, it generated noise which was *8 dB* up from the previously
measured 80 meter noise floor. Similar on 7 MHz - but not much on higher
bands.
The furnace has a wi-fi enabled thermostat control (Smart Hub) which lets
me turn the furnace on and off with an iPhone app while sitting at the rig
watching the noise floor of the P3 / SVGA display.
With help from RFI reflector and deep research on the manufacturer's
website - I found that Lennox has an EMI Filter Kit *604552-1*. The "kit"
was back ordered through the manufacturer - but the parts were readily
available from Mouser.
The kit is also called a "Line Suppression Kit."
Here is link:
https://www.lennoxpros.com/604552-01-kit---line-suppression/p/54W22
Kit consists of a CorCom 12EP1 AC line filter, wires, connectors and some
snap-on chokes. Plus, we added shielded thermostat wire.
Lennox has instructions for installing the kit. The instruction sheet (2
pages) was difficult to locate, but for reference it is numbered *507153-01
*and titled *"Installation Instructions for Electromagnetic Interference
Kit (604552-01) For Use with 90% Efficiency Modulating and Variable
Capacity Furnaces." *
Fixes installed:
1. Installed AC line filter - mounted inside the furnace - directly on the
blower housing (using self tapping screws)
2. Replaced existing unshielded thermostat wiring (approx. 40 feet long)
with SHIELDED CABLE.
3. Placed #31 toroids (with 5 turns) close to the ends of the thermostat
cable.
4. Place #31 snap-on ferrite on wire coming from the supply junction box.
This furnace had been newly installed - so I used the original authorized
installer. This will avoid potential warranty issues down the road.
Results:
Furnace RFI now completely gone - and noise floor back to where it was.
Now it makes no difference if this furnace is operating or not.
Also, this was the first time I used the WD8DSB Breaker Panel Sniffer
method. Before installing the furnace fix, I followed 'DSB's method shown
on YouTube:
https://www.youtube.com/watch?v=vDB8rAwVt5Y&t=146s
Double-blind research: Closed both my eyes and slowly moved the loop up and
down the panel until I heard high noise on a portable shortwave receiver
(Tecsun PL660). Then I opened both eyes and read the breaker's label:
"Furnace." After the furnace fixes - I repeated the Panel Sniffer Test:
and now, absolutely no RFI at the panel.
Thanks to all who have contributed knowledge and experiences re: furnace
RFI here on the reflector and the ARRL RFI pages.
73, Alan K0AV
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