Ethernet Wiring

It is not recommended for a few reasons.  The sharp edges inside the ducts can damage the wiring over time due to vibrations or expansion and contraction due to temperature changes.  In addition, there maybe signal interference due to static charges building up from the air flow. 

In addition, it may also be in violation of local, state, or federal building codes.  And keep in mind, for safety concerns, it is generally required that the wiring is plenum rated when run inside of a HVAC system.

It should be fine, and the duct might provide shielding. 😀 That said, I have switched to using a TP-Link extender with a Stack Audio Smoothlan inserted before my Innuos streamer. This actually sounds better than the 30’ Blue Jeans cable, in my system.

It can be installed in the air return ducting. You will need to use plenum fire rated jacketed cable though.

Other options for running the cable?  Is the floor in the room  pad and carpeted? It is possible the cable could be installed around the wall base trim under the carpet. Between the carpet tack strip and the wall base trim. 

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Clever!

Single family residence, no fire walls involved, as long as you are not passing thru any fire damper, preventing it from closing .... easy enough to seal with this stuff

https://www.homedepot.com/pep/Gardner-Bender-1-lb-Plug-Duct-Seal-Compound-DS-110/100212441?source=shoppingads&locale=en-US&pla&mtc=SHOPPING-BF-CDP-GGL-D27E-027_011_TOOLS_ACC-NA-NA-NA-PMAX-NA-NA-NA-NA-NBR-NA-NA-NEW-NA_Priority2024Ended&cm_mmc=SHOPPING-BF-CDP-GGL-D27E-027_011_TOOLS_ACC-NA-NA-NA-PMAX-NA-NA-NA-NA-NBR-NA-NA-NEW-NA_Priority2024Ended-21843354617--&gad_source=1&gad_campaignid=21843375815&gbraid=0AAAAADq61UeTNi23JBEM6IvS-SrR3pVC1&gclid=CjwKCAjwo4rCBhAbEiwAxhJlCaS4hL0IwUjHk7XTJFlSfB4xtuK0m54N8twzGgsU3O8RnOZ3_NHkwBoC78gQAvD_BwE&gclsrc=aw.ds

I made beads of this sealant to seal my woofers in my restored AR-2ax speakers.

Technically, this would meet building code.

3M Fire Barrier 1.45 in. x 6 in. Moldable Putty Stix MP+ Flexible 76