At our last house I remote mounted the pump on our spa so I would not have to hear it. I used 2" PVC. Did not make any difference in intensity. I insulated the pipe-helps with sound transmission and the obvious heat loss. I had envisioned a wood fired heater but we moved before I could do it. I had a buddy that lived up in the mountains and he built a wood fired box that was in the spa(a large wood tub) with a electric trolling motor to circulate the water. It would go from ice on top to 100 deg in a few hrs.

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Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT