heating a small pool

[GraceByDesign]

A person in my neighborhood has about 5 rows of 1 1/2" PVC, about 8' or 10'long, painted black, plumbed into his Intex donut... Certainly would be cheap, but I dont know how effective it is, tho. He just has it propped up on the sunny side of the pool.

<--to return<--------------|
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ETA the diagram did not show up correctly... the flow goes back and forth, not just up one side, tho Matt shot this idea out of the water anyway with his post below.

[matt4x4]

Large diameter pipe will give you almost no heat gain (unless you cover your entire lot with it). So if you go that way with 50 feet, you might get one or two degrees.
What you need is a manifold setup that divides your large inlet line into numerous smaller lines (same as a store bought panel).
The reason you have to do a manifold is to keep the pressure relatively even, forcing the water into one small line only would create a ton of backpressure and wreck your pump pretty quickly.

To retain heat, put a solar blanket on it over night, it will cut down on your incurred looses greatly.