http://kwcamerica.com/-hansa/images/product/10_501_134_480.jpg Obviously, I am a newb here, so thanks for reading my (probably simplistic) question. I've done a bunch of searching of the forums and didn't see what I was after. We recently moved into our new construction house which is configured with a hot water circulating pump. The idea being that a loop of pipe runs through the house and a small volume of hot water is always there circulating. When you turn on any hot faucet, the distance the hot water has to travel is just from the nearest point on the circuit, so BAM you get quick hot water. My plumber was eying our kitchen faucet dubiously the other day. A KWC Systema model (http://kwcamerica.com/-hansa/doc/technical/specsheet/10.501.134%20Spec%20Sheet.pdf" [Broken]), it has a regular spout and a pre-rinse retractable spray head. Beast of a faucet. Solid, heavy metal thing. There is one valve that controls flow AND temperature. It's is kinda hard to tell on the pic above, but a second valve on the base of the regular spout controls the flow rate to that spout only. (The spec sheet has a clear drawing of this) A third valve on the handle of the prerinse spray head is for the sprayer only. SO - we have been leaving the main valve on, to whatever temperature we need for awhile, and just turning the water on and off with the other two (non-temp) valves. The plumber says mixing is going on the whole time the main valve is on, even though the two other flow controls are off. Sounds like BS to me. The pressure in the whole house (hot and cold) ought to be the same when all faucets are off. The same supply line feeds the hot water heater and the cold pipes. I do not know if the faucet includes one-way valves (? check valves). But it seems to me the only downside of our method is a bit of heat exchange right at the interface between the two pipes in the kitchen faucet valve where they come together. Any advice or opinions? I've thought about using a medical-grade Doppler ultrasound machine to look for evidence of flow (I cannot hear any water running in the pipes), but I dunno how well sound will move through these pipes, if at all. (Most of the piping in the house is plastic, not copper).