Ethernet Wiring

I’m retired now but at my last work place they ran cat 5 through the building ducts and it was a huge improvement over the previously horrible WiFi that we had.  There were no issues over the year and a half of use before my retirement.  I chatted with installer who said that they do this all the time.  He said that he had never encountered an issue with warping due to HVAC, which was the first question that I asked.

  Ethernet cable is inexpensive.  Even if something did warp after years of use, replacing it should not be to painful 

Thanks to all for your helpful comments and suggestions. 
Greatly appreciated. 

@zlone

Is it possible that the TP-Link extender is introducing noise into your electrical power?  Similar to what dimmers do in home wiring?

Are you using any power conditioners?

@boulder_bob I have no doubts that the TP-Link is probably a bit noisy, but my house likely has several other devices that are just as bad. I spent last year working on my power and tried Furman, Puritan, but then settled on a PS Audio P15 regenerator. That pretty much fixed everything, Sunday night sound all the time now. 

I suspect the vast majority of audiophiles have a second rate setup for their streaming network. Modems and routers should be located near audio system, both should be powered via lps, short runs high quality LAN/ethernet cables. For those who've experienced the benefits of network improvements for streaming sound quality the above will further improve SQ. 

Beyond this, disable wifi on this router, run LAN cable from this router to second router which will serve as whole house router with wifi enabled. 

I see audiophiles spend large sums on things like network filters, audiophile switches while they completely ignore noisiest components in network chain. Seems to me having a clean source is superior to cleaning up a dirty source. Craziest thing is doing the above costs little compared to what some spend on some of these network devices. And I do have experience with audiophile switches/filters, not totally dismissing them.