Flow check before circ OK?

GW

Wet heads-

I'm looking at a small commercial job where I have to add in an indirect water heater. The current system has a tankless with NO flow check; the apartments have zone valves. There's a 2 1/2" main leaving the boiler; I would have to imagine the heat travels far up into the primary piping because there is no check in the non-heating season.

So, I can add in a take-off for the indirect, that's simple enough. My question is IF I opted to add in a
2 1/2" flow check, could I install it before the circ? I've never seen it in my travels. If it's not a good idea, I may have to drain down the primary which will add some time for me to purge.

Thanks for any input

Gary