You’ve got DWV (drain, waste, vent) fittings there. You need to use schedule 80 PVC pipe and fittings, the gray stuff.


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Manufacturer specifically recommends schedule 40. The factory installed fittings coming out of the heater are schedule 40.

40 and 80 are the same outside diameter. (edit: I've been told pools should be 80.)

Plumber that did my underground used flex, but only underground, and in the concrete.

Of the three homes I've owned with pools, none have/had valves for the heater. Water runs through it all the time. The valve after the heater directs it to the spa or pool. I also have valves before the pump to select drains/skimmers.

Check valve would be if the equipment is much higher than the pool, it will help the pump(s) prime faster, and keeps the lines from draining.

My first pool had the pump slightly downgrade at the water line, it was great for priming.

This is an above ground pool. The manufacturer requires a check valve between the heater and any chemical injector, salt generator, etc. to keep strong chemicals from flowing back into the heat exchanger.
I think I'm going to put a ball valve in it. That will definitely keep chemicals out of the heater when it's not in use.

Just make sure you're using a full port ball valve. Some have restriction and that might effect the flow through the heater.

Interesting, thank you.