[kwlug-disc] winter and furnace

[Tim Laurence]

 There is an excellent video by Technology Connections explaining gas
furnaces.
https://www.youtube.com/watch?v=lBVvnDfW2Xo

You can jump to the point about pressure switch here.
https://youtu.be/lBVvnDfW2Xo?t=747

The tubes connect the pressure switches flue, burners, room, etc. The
membrane converts the pressure changes in the switch to physical movement.
The pressure has a microswitch that is pushed or released by membranes
movement.

The furnaces validates burnt gases are going out by confirming the exhaust
pipe is not blocked (by not having pressure builds up) and that the exhaust
fan(inducer) is working because there is a mild vacuum on it's input.

All of these parts are really crude and simple. Yes, we could use modern
digital systems but the furnaces were largely designed decades ago for
robustness and reliably well before modern digital control logic existed.

On February 9, 2026 at 6:32:34 PM, William Park via kwlug-disc (
kwlug-disc at kwlug.org) wrote:



On 2026-02-09 14:54, Mikalai Birukou via kwlug-disc wrote:
>
>> There are these little pipes that go between enclosed area in furnace
>> and membrane switches to detect presence of pressure difference between
>> normal/room and that enclosed area with air/fumes flow.
>>
>> Other season, there was a burned ash in one of pipes, after burner, I
>> suppose.
>>
>> One more season, I gently blew in and out of pipe into membrane switch
>> to hear it flip. It got unstuck, and continued proper operation.
>>
>> This season, a pipe had a drop of water in it. Surface tension in a
>> small radius obvious stopped pressure difference from pushing membrane.
>>
>> I guess, cleanup includes dusting furnace, and blowing through some
>> pipes. :) Noting that three events happened over 15 years.
>
> Better word, little tubes, rubbery tubes few millimeters in diameter.
> Not pipes.

Where is this "tube"? What does membrane switch do?

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