flow control with DHW recirculation and Caleffi tank mixer

roundrightfarm

I'm considering installing one of these on an indirect fired DHW tank- http://www.supplyhouse.com/Caleffi-520519AX-3-4-Sweat-Outlet-Tankmixer-Water-Heater-Mixing-Valve-w-Gauge

Can someone explain how these work? Is it necessary to add a valve somewhere in the system to balance the recirculation flow rate in the DHW lines? When there is a draw for cold water, what prevents the recirculation pump from pumping warm water into the domestic cold water lines?

hot_rod

This mixer is unique in that it can close off the hot port 100%. So no need to add a bypass or balance valve on recirc systems

roundrightfarm

how does it work when there is a cold water draw from a plumbing fixture? Will the recirc pump pump warm water into the cold lines, flowing in the opposite of normal direction from where the cold water enters the portion of the unit where cold and the recirc return line meet?

BrightonDan

Just in case you're still considering this, RRF, or for anyone following this, I suggest checking out the install instructions, via the SupplyHouse.com link in your OP. The cold-water tee subassembly apparently includes a check valve for the cold supply.

Then again, I'm not sure you'd have a problem even without that check valve: for the recirc pump to push water into the cold supply line, the hot water would need to be replaced from some other source! (I'm ignoring thermal expansion.)

You'll need to install a check valve on the recirc line, or on the cold supply if you buy only the 520051A unit (without flex hose & coldwater tee & union fittings).

That's my reading of the docs. Please correct me if you understand otherwise. And please let us know what you end(ed) up doing!

I'm looking at that unit for my own house. (It's for a new combo unit that has a dedicated recirc-return port. I think I'll want to simply treat the recirc circuit like a normal cold supply.)