Considering Hot water recir system, advice?

ginahoy said:

Hi Bob, I've been curious about these for the reasons you mentioned, especially in homes where primary water heater is electric. But it seems like the cold water stored in the supply line would overwhelm the recovery capacity of the little 1.5kw heater. Of course, this wouldn't be an issue for just washing hands, but when showering or shaving, wouldn't the water run hot-lukewarm-hot?

David

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I thought I posted a reply earlier but it doesn't appear, so here again.

The POU heater in that setup work because water from the pipe mixes with the hot water in the POU heater.

If you have a 2.5 gallon heater at 140 F and 1 gallon in the pipe at 75 F, then as you use water the temperature will drop to around 115 to 120 degrees before water from the main heater arrives. If you want it hotter, you can set the POU heater to about 150 F, or put in a 4 gallon heater which will give you about 125 F when the hot water arrives.

Current showers have a temperature control that limits temperature to 120 F.

I shave after shower so the water in the pipe is already hot and there is no cooling effect.

jadnashua said:

You plumb the input of the point of use heater with the hot line, not cold, so as it starts to empty, it is refilled with the hot water. Since it is close to the outlet, you get nearly instant hot water.

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I must not have made myself clear. What I'm trying to understand is what happens as the initial tank of hot water empties. Sure, it's going to start out hot, but the incoming cold water stored in the hot water supply lines will quickly reduce the average temperature of the water stored in the POU tank. The little 1.5kw heater element can virtually be ignored -- you'd be lucky to get 10 degrees of rise at the typical shower flow rate (1 to 1.5 gpm from hot water side).

Do the Ariston units have sort of temperature-based valve that bypasses the POU tank when the hot water arrives? At least this would minimize the effect of the incoming cold water.

David

Bob NH said:

The POU heater in that setup work because water from the pipe mixes with the hot water in the POU heater..

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Hi Bob, I posted my previous response to jadnasua before seeing your post. I guess my assumptions were more severe... It's not uncommon to see 50 degree water in my hot water lines (uninsulated pipes, in 30 degree attic). But when I design my next house, I will run my hot water lines inside conditioned space, and minimize hot water runs. Even still, I think a POU heater in the furthest location (kitchen or bath) makes a lot of sense. Thanks for confirming.
David

Gary Swart said:

I've been using a Laing for about 3 years and I really like it. It requires a return line from the furthest away fixture back to the tank, which could be difficult to do in some homes. Besides the pump, the system requires a simple check valve, an air bleeder, and a ball valve. I replaced the drain spigot at the bottom of the tank with a nipple, tee, and ball valve. I got my pump new, in-the-box on **** for much below retail. There are systems that do not require a return, but I can't speak to their operation.

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I assume you installed the Watts FV-4M1 auto air bleeder that Laing recomends. Did you install it with the air scoop that their instructions say will bleed air while water is circulating? Without the air scoop, Watts says air only comes out if there is no circulation. I think this means that unless the air vent is located at the highest point in the piping system trapped air might not rise up to the vent and be bled out when the pump is not running. So with the air scoop, air is continuously bled during circulation. I believe that normally air is bled from the hot supply when a hot faucet is opened but this wouldn't necessarily take care of trapped air in the recirc line. Any thoughts on this?