Installing an “On-Demand” Hot Water Recirculation Pump

Many new homes these days are plumbed with a dedicated loop that circulates the hot water, often via gravity, to the fixture that is farthest from the hot water heater.  As the water in the hot pipe cools down it becomes heavier and drops down this dedicated line to the water heater in the basement and the hot water, which is lighter, rises through the plumbing up to to the fixture farthest from the heater.  This is great if your house has a basement and the builder was forward thinking enough to plumb it this way.  If not, or you live in a one story house, then you need an electric pump to move the water.  Many of these systems operate the pump via a timer that corresponds to your regular pre-work/shower routine.  These are ok if you keep a regular schedule but I prefer a on-demand system that only circulates the water when you tell it to.

Metlund

The pump and components.

The principle is the same, but an on-demand system has a button that activates the pump, circulating the water to the fixture it is closest to and automatically shutting off when it’s temperature sensor detects the arrival of the hot water.  The pump is located under the sink furthest from the water heater and can be configured with either a wired button or as a wireless system with multiple buttons for activation from multiple locations.  This installation was a wireless system located under a kitchen sink.

The system consists of the pump, a wireless sensor that attaches to the pump, 2 fittings that attach to the hot and cold water lines, and 2 flexible stainless steel water lines that connect the fittings to the pump.  When the pump is activated it pulls hot water from the hot side and pumps it into the cold water line, pushing it back into the water heater.  When the hot water arrives from the water heater the temperature sensor turns the pump off.  Turn on the faucet or a nearby fixture (shower or whatever) and the hot water is ready and waiting.  Since the pump is electric you obviously need a place to plug it in.  Most kitchen sinks today have an outlet underneath that is half switched (for the garbage disposal) and half hot (for the dishwasher).  Get yourself an adapter that allows you to plug 2 devices into 1 outlet and you can use the dishwasher outlet for the pump as well.  If there isn’t an outlet then one has to be installed, but that is something for another post.

The area will the pump will be installed.

The plumbing portion is pretty straightforward.  The 2 special fittings attach to the hot and cold water pipes coming out of the wall, and the original shut off valves that you just removed from those pipes (after you turned off the water, or course) are reattached to the new fittings.  The fittings provided assume you have half inch copper water lines and compression shut off valves, both of which this kitchen had.  The other opening on the fitting is where the stainless flex line attaches. One end on the fitting, the other to the pump.  Once all the plumbing connections have been made, attach the wireless sensor to the appropriate color wires on the pump and attach the sensor to the side of the cabinet wherever there is room for it.  The first time you plug the pump in it will automatically activate.  You will hear a change in tone as the pump fills with water and begins the recirculation.  If the pump seems to run and run and you don’t hear a change in tone it probably has an air bubble stuck in it.  Turn the hot water on and off quickly and repeatedly while the pump is running to jar the bubble loose.  Next time you need hot water just push the button, wait a minute or so depending on your distance from the water heater, and the hot water will be right there when you need it.

The installed system after everything is back under the sink.

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