Re: Getting instant hot water at all sinks/showers
Posted by Dick -- Alaska on February 13, 19101 at 00:55:15:
In response to Re: Getting instant hot water at all sinks/showers
Don't want to simplify this discussion too much, but my plumber and I worked out a no-moving-parts solution for "instant hot water" 40 years ago which I'll describe for what it's worth:

We have a conventional tank-type water heater with a standard drain cock on the bottom of the tank for occasional flushing of any sediment or if for some reason the tank needs tobe drained.

We shut off the water, drained the tank and temporarily removed the drain valve. A "tee" was inserted between the valve and tank. A ball valve was installed into the side opening on this tee. We then ran a small (1/2") soft-drawn copper tubing, the kind approved for dishweasher hookup, etc., from the ball valve at the tank base to another tee close to the most-distant hot-water tap. Try to "grade" this line so it slants upward to its far end as much as possible. (If this "return" line needs to be routed to two destinations by adding a tee in-line no problem, but one distant tap may stay a little hotter than the other.) For good practice, put a ball valve on this tube right at the water-heater tee. If (unlikely) water at the tap becomes too hot, the ball valve can be used to limit circulation slightly. It will help operation and save a bit on energy if both the original hot-water lines and the new "return" line are insulated with inexpensive snap-on foam pipe insulation, but if mostly inaccessible, try to insulate wherever it is accessible.

When the setup is complete, slowly open the ball valve and check carefully for leaks in the new joints. Flush the distant hot-water taps until bubbling stops, especially those on upper floors, to eliminate as much air as possible in the "loop" you have created. Air left trapped in the lines will eventually absorb into the water and be carried away, and the system won't work well until any air trapped in "high spots" in the lines is absorbed or carried away.

Theory of operation: Heat--and hot water--rises, so the water at the top of the water heater is hotter than at the base of the tank. Originally the hot water supply terminates at a closed tap, so aside from warming a few inches from the top of the tank, there is no circulation within the line since the fixture tap is normally "off".

With a loop created, the slight "upward pressure" of the hot tank-top water "pushes" the water in the hot water line upward which in turn pushes the unheated water in the "return" down and back through the tee at the base of the heater. Circulation occurs because the returning "cooler" water is drawn back into the heater and replaces the hot water now rising out of the top of the tank.

One contributor mentioned the risk of cross-connecting hot- and cold-water lines and I agree. Note that in this setup all plumbing and circulation occurs ONLY within the normal "hot" water line and water heater, and the cold-water line is not involved in any way.

I just mentioned the returning water was cooler. In real life, once everything warms up and is circulating well, especially if insulated, I can tell you the "returning" water, even using a little 1/2" return line, is anything but cool after a day or so. This arrangement works like a champ, at a total material cost of a 60' roll of copper tubing (or DEX cross-linked PE, etc.), a couple of tees and a couple of valves. And, as I said, no moving parts, sensors or tricky controls. Less is more wif you can pull it off.

This loop also adds another slight benefit in that it helps keep the entire water heater filled with top to bottom with almost-uniform hot water, automatically providing a slightly higher reserve for those periods of high usage in the morning(!)

In our installation, we didn't bother to carry the loop all the way to the farthest hot-water tap. We simply terminated it at the point where the comparatively short hot water branch lines finally left the main supply line. Since water travels very quickly through typical 1/2" branch lines, opening a tap produces hot water in seconds. If that proves too slow, the "loop" can be extended right to each tap if desired.

Don't know how this would work in a single-level ranch-type home, but should not be a problem so long as the "return" line is installed somewhat lower than the hot water "supply" and the supply side is graded upward to as close to the taps as possible.

I'm a registered securities representative, not a plumber or pipefitter, but over the years I have learned more about residential systems than I really wanted to know due to owning substantial rentals. Hope this helps in your thinking.

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