u/O2Dive

Thought yall might appreciate this. After acquiring the card as a teenager (early 90s)I mailed a new ball to Brooks and he sent it back in a hand addressed envelope (in the background).

TLDR: is there a temp sensitive valve that could help prevent cold water mixing into the hot outlet?

Since installing a small under-sink “instant” HWH the time to get hot water from the main tank is increased.

Originally the wait for hot water at our kitchen sink was about 3-4min (roughly 1.5-2 gallons). That’s a lot of wasted water and really impacts the dishwasher cycle (about half or more of the cycle would only be pulling the “pre-hot” water i.e. cold water)

So I had a small “instant” electric heater (2.5 gal or so) installed under the kitchen sink.

Now we get 2.5 gallons of nice hot water right away. Great. BUT it now takes LONGER for the hot water from the main 50 gal HWH to come out of the faucet.
So now we get about 5-7 minutes of kinda lukewarm water before it gets to the temp of the main heater.

I suspect what’s happening is that after emptying of its hot water, the instant water heater is behaving like an additional 2.5 gallons of pipe between the main heater and faucet. So it refills with cold water that then slowly mixes with incoming hot water at increasing percentage but not until that whole volume is replaced completely with “main “ hot water smdo I begin to feel that temp coming out of the faucet.

So is there a better way to pipe this to prevent that? Or perhaps a temp-sensitive valve that shuts when the outlet temp from the instant heater is below a set value?

(Drawing is flipped for simplicity, my hot/cold are on the correct sides👍)