DIY solar heater question

[Gomez5693]

I understand what you're saying. My goal was to extend our season by a couple weeks as cheaply as possible for now. Next spring we'll move the pool to where it will get more sun and that will help keep temps up.
I currently have 200' of 5/8 hose and 150' of 3/4 hose attached, which I realize is still no where near the surface area you are talking about. The main section of the manifold is 1.25" so shouldn't cause much additional restriction when wide open. At half closed I can hear a difference in the pump, so I plan to stay just over that. Tomorrow I hope to measure how much flow is going through the garden hose and at what temperature it is coming out.

[mas985]

If you bypass most of the water around the hose, then the water coming out of the hose will likely be high due to the lower flow rates but that just means you are losing a lot of heat to the environment. The idea is to have high flow rates through the panel and have very little heat rise. This is what maximizes heat transfer and efficiency.