Valve to bypass heater based in incoming water temperature

[rural_engineer]

Is there a valve that could be used to bypass a water heater when the incoming water is above a certain temperature? I'm considering putting an under-sink 2.5 gallon storage water heater in my kitchen, which is far away from my main 80 gallon storage heater. It would pull from the storage tank, so the incoming water will warm up with continuous demand. Once the incoming water is hot, I would like to bypass the heater, giving it a chance to re-warm the water from the pipes. Is there a valve that will do this?

--John

 

[Jadnashua]

What most people do is to connect the inlet to the small WH from the hot line normally feeding that faucet and use the outlet of the new tank to feed it. It needs to be large enough to purge the incoming lines before it cools off, then, it would essentially just be a pass-through of the hot water from the main water heater. Once you stopped using hot water, the smaller, local tank would keep what's there hot as the supply line cools off.