My Brother has a new home he had built last year. In his master bathroom (furthest sink from the water heater) under the sink he has a mixing valve installed(Watts MMV-M1). The hot port is connected to the hot line for the sink and the cold port to the cold line but The mixed port goes down onto the floor and I'm not sure where it is connected to. The plumber told my brother that this would help get the hot water faster to the fixtures without installing a recirculating pump (which it seems to do) I'm wondering if someone can help me get my head around how this works! Thanks

Thanks for the response. Where do you think the "mixed" water would tie back into the system? Close to the water heater?

If it were a thermostatic mixing valve, the "mixed" connection would go to the faucet, NOT into the floor. Theoretically, it should not work.

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If there is no "flow" other than convection currents, the cold water will NOT mix with the hot water through a tempering valve.

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Pretty slick....It sounds like he set it up as a gravity recirc, not uncommon. The slick part involves the thermostatic mixing valve. He can run the temps at the water heater much higher and not worry about scalding someone. It's important to run the water heater at 140*, at least, to avoid Legionella.

Pretty sure that is the recirc line that ties back into the water heater. That mixing valve has a spool that moves according to temperature.Usually they are used to add hot or cold to control temperature, but I think in your case,it is either recirc or not based on temperature. No recirc, the water cools, the spool moves to add hot, and allows recirc.Some speculation, but that makes the most sense, in the absence of a pump.

Ok, so I was wrong, if you ask my wife I always am, this valve is connected to the soaking tub next to the sink (not sure why I didn't think of that) Turns out another sink has a "Comfort Mixing Valve" its black plastic with 4 ports. similar to this [www.amazon.com] My new question is after reading about this valve it seems it needs to be used in conjunction with a circulator pump. I don't understand why this is necessary and I know my brother does not have one. Any thoughts? Thanks