Looking for some guidance on plumbing. Currently heat pump is plumbed with the connections for my gas heater valved and waiting. What I would like to do is be able to close off one or the other or both heaters. As learned on TFP, gas early and late season with heat pump mid (in Central PA). Is it worth not running salt water through the heater not in use or ? Just looking for best longevity for my heaters. If someone could provide the correct way to plumb these, I would appreciate it!

Thanks - Ted

Interesting question. I'll be curious to read answers from the pros.

No doubt you'll lose some restriction by bypassing the heaters, which will increase flow. On the other hand, you'll have stagnant water sitting inside the heaters for months at a time.

You could do as you say and then replace the drain on the heater with a ball valve so you could drain the heater whenever you bypassed it.

Anyone have pictures of heaters with valves installed in plumbing to isolate?

I have both a gas heater and a heat pump. I did plumb the gas heater in series with the HP with one valve that I can bypass the ga heater. But honestly I never used it. I just run the water thru the entire circuit all the time (pump, filter, gas heater, heat pump, swcg, return to pool). When I use the gas heater, I just turn the HP off. Even if I didn't turn it off it wouldn't kick on since the water running thu it is warmer than the HP set temp anyway. When I use the heat pump, I turn the gas heater on standby.

Which is obviously functional bk, but doesn't that impact the life of the internals of the heaters? Copper, cupro nickel, Titanium.... those plus salt water and/or other chemicals flowing through them when not needed, vs valving off and draining when not in use for long term? Or is this not a big deal??

It's really not anything I worry about. If you only had one heater would you put a bypass in? I suppose you could but I've never seen it done ( just because I've never seen it doesn't mean people don't do it). Besides, I'd rather have flow rather than have water just sitting in there. A heat exchanger is hard to drain really without blowing it out.
I think the worry of corrosion from pool water is overblown. The thing is designed to heat pool water.

We are a builder and bypass all heaters because when the heat exchangers leak you have to shut the system off while you are getting the parts. With byass you can maintain water quality because you can still run your pump

Meh, I suppose. How often is that likely to happen? I guess valves and pipe are cheap enough.
The question was, however, do you need a bypass for a situation specifically for 2 heaters. I would say no. Just run them in series.

Also need to check heat pump owners manual for max flow. Pentair is 85 gpm(I think) on heat pump anything over that needs bypass for

You are supposed to install a pressure relief valve, and flow switch when you install a valve on the outlet side of any boiler.

Otherwise you could trap pressure in the system allowing the heater to fire, and boom goes the dynamite!