If I ever can figure how to upload pics with this new VBulleting software I'll post a couple. Back in 1999 I first experimented with 400' of green garden hose. Was tightly coiled on a 4x8 sheet of plywood, painted black, covered in plastic wrap, and configured in 4x 100' sections. I built the 1x4 manifolds out of PVC. That was a proof of concept for what followed. Final heater was 1200' of black poly pipe in a 12x100' configuration, again with PVC manifolds in and out, layed in the back field on black rolled roofing that occupied roughly 8x50 feet. I diverted some of the return flow through the heater and just dumped the heater output in the deep end. Yeah, they work, not as efficient as a mat, but a lot cheaper, not as pretty, but probably more rugged. Space is the thing to have and I have plenty of it. When the grass grows in my uncut back field you can't even see it. The feed pipes are 1.25" buried black poly.
Al