@nprofile1qqswcnfyrse5xydn5vzyx0hrgs4798gw3rn7cxdctm0jhw3fhy6ktcspy3mhxue69uhkummnw3ezuerfva5hgctvwfjkvmmjd4shg6t0dchxjmnxduhsz9mhwden5te0dehhxarj9e3kscttv4ezumn9wshsz9thwden5te0wfjkccte9ehx7um5wghxzaf0hmdh0f had put some black tubes on his roof to heat his pool. Last year I had setup a pool myself and tried to do the same. With quite some work and not really knowing what I was doing, I hooked up a 650W pump to my pool but later realized that my approximately 1 square meter of roof installation probably wouldn't make a dent on my 9 square meter pool. But while in the pool, the water from that hose being 2°C hotter than the pool always felt warm even though 27°C isn't really hot-tub territory.

That pump died over our southern winter or turned so loud that it wasn't usable anymore so I got a 120W "silent" pump. And yes, this pump is really silent although I found their advertisement a little misleading. They advertise "30dB", claiming that plants are at "0-25dB".

And now I did some math: With 6.5 liters per minute and a now 3°C increase, this 120W installation pumps 1360W into the pool. As I did not measure the flow of the loud pump, I don't know how that stacks up but in terms of Wout/Win it's almost certainly better now and better than an air-to-water heat pump.

I am still looking for some cheaper black stuff to have water flow through as all options I found so far are kind of terribly expensive per square meter.