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Need help with my furnace

Mar 10th, 16:59

k8fff

Joined: Jun 22nd 2021, 10:16
Total Topics: 0
Total Posts: 0
No, I don't mean my house is cold. My furnace makes horrible RFI when it runs. It's mostly on 20 meters, but it's also on 40 and 80 and 10. I just moved into the house and I really don't know much about the HVAC equipment here. It's an American Standard condensing gas furnace - the kind with two PVC pipes to the outside for combustion air intake and exhaust. The noise starts as soon as the thermostat calls for heat and the burner kicks on; it doesn't wait for the furnace to get warm enough that the blower runs. The noise is there as long as the burner is running, and quits when the burner shuts off, even though the blower is still running.

The Google tells me that the igniter is a hot element. I don't know if the igniter shuts off once the burner is lit, or if it stays on all the while. The Google also shows that there'a a circuit board in there somewhere, but I haven't found it yet, nor can I find any information about its function or operation. I also think there's a fan for combustion air, but I'm not sure about that either. I am hesitant to start taking my furnace apart...in the winter...in Michigan.

So, anybody have any ideas where I should start looking for an RFI source?
Mar 11th, 07:51

W1VT

Super Moderator

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Variable Frequency Drivers for furnaces are notoriously noisy. Not only is the shape of the waveform bad but a lot of power is involved. You may not only need to filter all the wires to stop them from acting as antennas, but improve the shielding so you have an effective Faraday shield around the wires. Alternately, getting distance between the wires and the receive antenna may adequately reduce the interference to tolerable levels.

Zak W1VT
ARRL Senior Lab Engineer

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