Hot Water Recirculation System

In the paragraphs to follow, when I say “…if it were up to me…”, please realize what I mean is that if I were making decisions on a new house being built, or if the water heater failed and needed replacing, or if any-number-of-other-circumstances meant that it wouldn’t be wasteful to discard appliances and/or fixtures which are currently working just fine. Big if.

That having been said… if it were up to me, I would not have a large tank water heater. It would not be electric. It would likely be a pair of tankless, natural gas, instant-on water heaters; one near the North end of the house where it would supply the downstairs and upstairs bathrooms (their directly above/below each other), and another in the (South end) laundry room to supply the clothes washer, the dish washer and kitchen sink directly above the laundry room. Even though the pipes are insulated, it’s the long (East-facing rambler) run from North to South in a cold basement that has caused us to run countless gallons of water down the kitchen drain waiting for the water to get hot.

From the top of the water heater all the way up, it used to be rigid 7/8" OD copper.

From the top of the water heater all the way up, it used to be rigid 7/8″ OD copper.

But – an inexpensive and easy compromise for the time being is a Hot Water Recirculation System. I just installed one today. It was one of the easier plumbing jobs I’ve done, involved only two minor thumb injuries (nearly no blood), and a total cost under $200. I watched a couple videos online of people describing their installation of this very same unit, and although they only needed about an hour, and needed zero to two parts beyond what came in the box, in both cases it looked like their house was built decades more recently than this house. Stuff was easier to get to. Hookups were flexible tubing at both ends.

Mine would need more parts, and more trips to Home Depot. Oh well.

5:30-6:45am, 5-6pm, 9-10pm

5:30-6:45am, 5-6pm, 9-10pm

So the idea is that if all of the hot faucets in the house could begin deploying water warm enough to wash one’s hands within several seconds (rather than a full minute at full open), less water is wasted. And presumably, it is more energy efficient to allow the water in the hot-side pipes to cool to room temp during the times we’re extremely unlikely to need any hot water. So we have three hour-long periods of please-pre-heat-the-pipes established. Getting ready for work in the morning, dinner and dishwasher time, and getting-ready-for-bed time.

After we use it like this for a while, we may adjust those start/stop times. We may even find we only need two periods.

The real

The real “brains” of the system, is a semi-dumb crossover valve that opens at anything below 85 F.

The “normal” way to install this crossover is to put it under the kitchen sink. The (assumedly) flexible supply hoses that go from the under-sink shut-offs to the kitchen faucet are connected instead to the “out” connections of this crossover. Then two new flexible supply lines go from the shut-offs to the “in” connections. In our case, I lucked out. There used to be a non-code-compliant shower in the laundry room. So there were overhead hot and cold supply lines with big 1/2″ copper and union connections. I cut the pipes above the unions, and put on brass compression fittings. Larger “supply” than usual, but it worked, and it’s only another six feet of pipe to the kitchen faucet from here. Close enough. Then I merely capped off the “hot out” and “cold out” supply connections on the crossover. That’s the white PVC caps you see in the photo above.

Top to bottom, rubber washer fitting above pump, another rubber washer fitting below, then a thread-goop nipple into the tank.

Top to bottom, rubber washer fitting above pump, another rubber washer fitting below, then a thread-goop nipple into the tank.

I figured if any of these new connections was going to leak, it would be the galvanized (dielectric plastic insert inside it) nipple that went into the tank. No sign of trouble there yet.


7/8″ OD copper with brass compression fitting.

But this one – above the pump, top end of the flexible hot supply, this one took the most torque to get it to quit dripping. I suspect it’s related to how deeply the stamped the lettering is along the side of the copper. You know… so that I know that it’s copper (and what size it is). The half-inch stuff at the other end either wasn’t stamped, or I lucked into an un-stamped area. Whatever the reason, it took a lot less torque than this one.

Here we go again… but if it were up to me, something like this would be required in every home West of the Rockies. And no, you can’t have a golf-fairway-like lawn if you live in a place that nature has decided should be desert. No irrigation for vanity – only for growing food. But this is just one in a very long list of reasons that California (and the other Western states) would never want me to be their king.

The great thing about this is that I didn’t do it in order to choose personal suffering for environmental reasons. Rather, it was a situation where my convenience AND saving natural resources align nicely. I’d rather not waste time nor water nor money waiting for the water to heat up at the sink.


6 comments on “Hot Water Recirculation System

  1. Phil Lefever says:

    Kelvin, neat job! These re-circ systems do indeed save energy, water and time especially in homes with long runs. My house works fairly well without one as I don’t have a hot water line longer then 12 feet.

    I’m not sure a tankless heater works here in MN, winter water temps can approach 40F and they just don’t give enough rise. I do hate the standing tank since the flue has to go through it creating flue losses. When I update my boiler I plan to install one that will do hot water heating too so the storage tank won’t incur flue losses.

    My brother in Maryland built a system years ago where he uses a heat exchanger to recover the waste heat from his central AC condenser to heat his hot water. During hot weather there is no need to burn gas to heat water!

    Have you converted to horizontal axis laundry yet?

    72, or 73

    Phil, ‘NES

  2. kelvindean says:

    I know a few people who have tankless water heaters. Dunno if they get scalding-hot water from them, but they do enjoy the energy savings, and the never-runs-out thing.

    Will have to look up horizontal axis laundry. Does that have a non-geek term?

    I have recently begun having my shirts laundered professionally because I’m sick of ironing. Pilgrim Cleaners is at ground level, about 2 miles away – horizontally… whereas the laundry appliances at our home are downstairs – as much vertical distance from the bedroom closet as horizontal. I’m betting that’s not what you mean.

  3. Phil Lefever says:

    The only thing I worry about really hot water for is the Dishwasher, it really needs to be 130F minimum, especially now that phosphates no longer boost the detergents. You can use the heater in the DW as a boost heater tho In the dead of winter I’m not sure a tankless can get the near 90 deg rise needed, although a dishwasher isn’t all that high a draw rate.

    I’m all for the energy savings of a tankless, although I’m not sure you would ever break even with one. Gas tankless heaters are ‘spensive, several times the cost of a standard gas WH. If you are going to electric tankless (which is handy as they can be placed wherever without venting) then costs go up due to higher priced energy. In my situation I don’t see tankless as an option.

    Horizontal Axis = front loading washer. If you wish to save, water, energy, detergent and the life of the clothing a fl is the way to go. I predict that in not too many years the top load style of American laundry will go extinct for the most part.

  4. kelvindean says:

    Ah… I had a hunch that meant front load. Not an option for us. My wife is a knitter, and when felting fabric, the way a top load agitates is far more effective, plus you need to be able to stop it, open it up, check for size, agitate it more, repeat, repeat.

    As for adequate temp rise, a real extreme solution would be a long coil of copper tubing before the intake of the tankless WH. Allow the winter cold water to chill the basement a bit.

    As with all these things, larger families with teen girls will have a greater chance of seeing financial payoff. And, as with all of these things, I’m willing to lose financially a *little* in favor of environmental payoff.

    So I’m having a big bonfire to set ablaze all my gasoline vehicles, and getting an electric car… you know… for emissions reasons. heheheh

  5. Phil Lefever says:

    Are you an LED Lighting guy too then? I’m 99.5% solid state at this time (the bulb in my self cleaning electric oven must remain incandescent due to the heat… for now). I started to convert about 7 years ago when the LED market wasn’t quite as good as today. I’ve done all my 4′ linear fluorescent lamps too now. Except for my constant experimenting, I may never need to change a lamp again 🙂

  6. kelvindean says:

    Yes. We’re not quite 50% LED at this point, but as the old ones blow, they get replaced with LED. I haven’t done anything yet with the long tubulars in the basement, and there’s one that doesn’t work. I’m resisting going and getting a new FL tube. Simultaneously, resisting doing *anything* about it ‘cuz how much light do we really need in a space we don’t use?

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