Plumbing installation – hot water routing

I mentioned the tree analogy that guides the plumbing layout in a previous post. Conventional wisdom is to have a trunk line with branches to each fixture.

In our case, conventional wisdom would have dictated three hot water branches serving the three hot fixtures – kitchen sink, bathroom lavatory and shower.

In order to minimize water and energy waste while cutting down on the hot water delivery time, we decided to rely on an on-demand hot water pump. The on-demand pump, once activated, will take a few seconds to prime the hot water trunk and branch line.

But this throws a wrench (pun intended) into the typical trunk and branch layout. We don’t need to reinvent the wheel, but have to fall back on recent developments in the hot water routing business.

To get the most out of the on-demand system, all three hot water fixtures should line up in series on one branch with the pump placed at the end, just prior to the last fixture, which in our case is the shower. The branch in turn supplies hot water to each fixture through short twigs.

We need to be mindful of the branch routing to keep the twigs as short as possible. The shorter they are, the more it cuts down on the hot water delivery time.

Data published by my friend and hot water guru Gary Klein, which I had listed in a previous post, makes for some simple math with interesting results.

  • The hot water twig to the kitchen faucet is about 36 inches long, delivering hot water from the primed branch in less than 1 cup (0.64 cup, to be precise). The corresponding hot water delivery time is less than 2 seconds at a fixture flow rate of 1.5 gallons per minute.
  • The hot water twig to the bathroom lavatory is about 40 inches long, delivering hot water from the primed branch in less than 1 cup (0.71 cup, to be precise). The corresponding hot water delivery time is less than 5 seconds at a fixture flow rate of 0.5 gallons per minute.
  • The twig to the shower head also is about 40 inches long delivering hot water from the primed branch in less than 1 cups (0.71 cup, to be precise). The corresponding hot water delivery time here is less than 2 seconds at a fixture flow rate of 1.5 gallons per minute.

I think it is fair to say that this qualifies as almost instant hot water delivery, once the on demand pump has primed the trunk and branches.

The priming would be initiated through the push of a button, typically first thing in the morning on the way to the bathroom, or in the early evening after the first person is back home from work. Anyone else using hot water after the priming and first use literally has instant hot water. That instant hot water lasts for two hours or more, thanks to the pipe insulation we used on our plumbing system.

This is not your typical approach to plumbing installation. It requires getting used to and focus on the part of the plumber to avoid falling back into the conventional trunk and branch system, which does little for water and energy conservation.

About Marcus de la fleur

Marcus is a Registered Landscape Architect with a horticultural degree from the School of Horticulture at the Royal Botanic Gardens, Kew, and a Masters in Landscape Architecture from the University of Sheffield, UK. He developed a landscape based sustainable pilot project at 168 Elm Ave. in 2002, and has expanded his skill set to building science. Starting in 2009, Marcus applied the newly acquired expertise to the deep energy retrofit of his 100+ year old home in Chicago.

5 thoughts on “Plumbing installation – hot water routing

  1. They actually liked the whole layout – once it was explained and once they understood the rationales. They are plumbers after all and like good solutions.

    That said, I am pretty sure they still called me crazy German hippie (or control freak for that matter).

  2. LOL

    Right now I’ve got a serious case of envy. Our hot water delivery is ridiculously inefficient. We have a VERY long pipe run from the water heater to our kitchen and bathroom fixtures, because the water heater is installed near where the gas main comes in from the street, not near the fixtures. 🙁 I have to turn on the hot water spigot at a trickle and let it run for several minutes to start getting hot water. I normally use a pot or bucket to capture much of that water and use it for watering plants, rinsing the tub after a shower, etc. It’s a pain in the butt – something we’ll need to change in the future.

  3. Anne, whenever you replace that water heater of yours, see if you can relocate it right next to the plumbing wall. Extending the gas line will be easy.

    For right now, you may want to consider insulating the long hot water line – but don’t use the cheap pipe insulation you typically find in the home improvement stores. Although it cheap, you’ll waste you money on it because it barely insulates.

    It almost sounds that you would be a perfect candidate for the on-demand hot water pump. I think I put a little more information up in the next post.

  4. It would be a major project, because the logical area is in the finished part of the basement. We would have to rearrange the space in order to make it work. We’ll look forward to your next post.

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