When we remodeled the two panels that Abe’s dad had found in the junk, we used PEX pipe. It is a lot cheaper than copper and much easier to install. The setup worked well, heating water consistently to 125 degrees.
However, on two separate occasions, the PEX split. The first time, we replaced the pipe, and made some adjustments to our design. It worked fine for a long time, but then recently split again. I guess it just gets too hot in there.
Hopefully, that will now last.