On-Demand Hot Water Recirculation Pump

Using an off-the-shelf timer/relay to pump the hot water closer to your faucet.

Press button, light goes on, when light turns off, your water is ready and waiting!

Background:

Although I no longer live in a drought stricken area, having grown up in California, I am always very mindful of wasting water. I'm also mindful of wasting energy.

In my bathroom, it takes about a minute of running the water before you get hot water. You have the choice of either washing your hands with cold water, or wasting a lot of water with the tap on.

With a typical hot water recirculation pump, it runs all the time, both taking energy to run the pump, but also it radiates heat along the path of the pipe constantly, making your hot water tank work more.

With this solution, as you enter the bathroom, you press a button, and when you are done with your business, there is hot water waiting for you with almost no water wasted.

Is this for you?

This project requires a "return line"... a way for the water already in the pipe to go back towards the hot water tank. This project is ideal for new construction, remodeling, or if a large amount of the plumbing is accessible. In my case, a large section was accessible in the basement, and then it went up a wall that I removed the sheetrock to access. I highly recommend using PEX plumbing, because you can fish it between floors, just like electric. I have been able to run PEX line only using 6" holes in sheetrock and using this patching technique:

https://www.instructables.com/Fix-a-Hole-in-Drywal...

With PEX, you can also use push-fit fittings such as SharkBite. If you plan on doing a lot of plumbing, I would spend $25 on a crimping tool that ends up saving you a lot of money over push-fit fittings. When buying fittings, make sure you check that they are all lead-free and safe for drinking water.

Circulation Pump:

https://www.amazon.com/gp/product/B0824JLB8N/ref=p...

From Pump threads to PEX (using crimps):

https://www.amazon.com/gp/product/B07CVRH9Z9/ref=p...

OR using push-fit: https://www.amazon.com/SharkBite-U088LFA-4-Inch-St...

Shut off valves (using crimps):

https://www.amazon.com/gp/product/B07K1XYZ6H/ref=p...

OR using push-fit: https://www.amazon.com/EFIELD-H%C3%B6ger-Valve-Pus...

Check valve:

https://www.amazon.com/SharkBite-U2016-0000LFA-Che...

Relay Timer: (I bought this one, which is a 2SPDT but you can buy a 1SPDT, and it should be cheaper)

https://www.amazon.com/gp/product/B083Y4ZSBY/ref=p...

Push button:

https://www.amazon.com/dp/B07F9PLSRY?psc=1&ref=ppx...

Inline fuse:

https://www.amazon.com/gp/product/B08JQ8S1XK/ref=p...

Indicator Light:

https://www.amazon.com/Indicator-Replacable-Mounti...

Electric Cord:

https://www.amazon.com/Bergen-Industries-Inc-PS615...

From your local hardware store:

Pex pipe (here is 3/4 as an example)

https://www.lowes.com/pd/SharkBite-3-4-in-x-50-ft-...

Pipe insulation

https://www.lowes.com/pd/Frost-King-0-75-in-x-6-ft...

1-Gang Square Metal Electrical Box Cover

https://www.lowes.com/pd/STEEL-CITY-1-Gang-Square-...

An electrical box

https://www.lowes.com/pd/RACO-2-Gang-Gray-Metal-Ne...

An electric outlet and matching face plate

Push fittings such as these- check the existing size of your plumbing, this is 3/4", but 1/2" is common as well:

https://www.amazon.com/SharkBite-U370LFA-Plumbing-...

If you are going the crimping route, you will need some fittings. Here is an example of some 1/2" fittings:

https://www.amazon.com/BRASS-PEX-FITTINGS-EA-ELBOW...

Pex tools (optional):

https://www.amazon.com/gp/product/B074K6R4D2/ref=p...

...and don't run short of crimp rings if you buy the above

https://www.amazon.com/Ispinner-40pcs-4-inch-Stain...

If you need to hang the pump from the ceiling:

https://www.lowes.com/pd/AMERICAN-VALVE-2-in-to-2-...

...and

https://www.lowes.com/pd/AMERICAN-VALVE-1-2-in-to-...

... and

https://www.lowes.com/pd/Hillman-3-8-in-dia-x-3-ft...

... and

https://www.lowes.com/pd/AMERICAN-VALVE-3-8-in-to-...

This project requires two parts, plumbing and electric.

For the plumbing, this is the basic diagram. You will be adding the return line (in grey). At minimum, you will be adding a tee at the cold water line into the hot water heater, a tee as close as you can get to the hot water input at your sink, a check valve, the pump itself, and I also added a shut off valve (yellow dots) on either side of the pump so that, in the event that the pump failed, I could quickly disconnect it from the system by simply shutting off the two valves, and unplugging the pump. You may also need some elbow fittings, just to navigate going through your house. You might consider using brackets to keep your plumbing from flopping around, and there are also brackets to hold your pex plumbing in a gentle sweep instead of breaking the pipe and using an elbow.

The pump has a low, medium, and high setting. You would choose the low setting if it were running constantly, but in our case, we want the high setting, since it is "on-demand", and we want the water to get there the fastest.

I also added pipe insulation wherever I could. This also should help keep the water hot for longer, or should you ever decide you want to have your circulation pump run continuously, you won't waste as much energy.

For the electric, the basic idea is just to create a "switched" outlet. This is similar to an outlet that you can turn on or off via a light switch, so a lamp will turn on or off. In this case though, it is the timer/relay that is turning on the switch.

Wire the outlet as you would normally, but put the timer/relay in between the power-in line using the bottom bus terminals.

I already had a good amount of 18-2 wire for an alarm system, so that's what I used, but if I didn't have wire yet, I would buy 18-3 wire and only run one wire instead of the two that you see in the photos. As I showed in the overview diagram, the light could be powered by the red wire, the button by the blue wire, and the green could be the return for both of them. (Sorry I changed colors for the electrical box detail diagram!) Make sure you put an in-line fuse on both the red and blue wires.

The indicator light can then be also powered by the outlet, wire an in-line fuse to the outlet's unused "hot" screw terminal to power it. Make sure the light is a very low amperage 120V light. (I actually purchased this indicator light at Grainger) I used a 1 Amp in-line fuse (yellow in the wiring diagram) so if there was ever a short in the wire, it would not cause a fire nor shock anyone very much.

The relay-timer also needs power-in and neutral on the top bus.

Lastly you need the button wire. The relay-timer also barely needs any amperage to know when the button has been pressed, and so here I also put in a 1 Amp in-line fuse on the button power line for the same reason, you don't want there to be more amperage than you expect, that probably means there is a short and you could cause a fire!! This is extremely important! You also want a momentary button which is rated for 120V. The momentary button wire should terminate at the center bus terminal at the top of the timer-relay. You will also need to cut a hole in the "1-Gang Square Metal Electrical Box Cover" for the timer-relay. I used a Dremel and small metal cutting abrasive disks.

On the bathroom wall, put in an old-work PVC electrical box, and run the two wires to it. I drilled two holes in a blank plate to mount the button and the indicator light, and attached both to the plate. I soldered the button wire to the button, brushed some "liquid electrical tape" over it, and grounded the button base. I used wire nuts on the indicator light, as the lights come with a pig-tail (wires already attached).

The timer/relay is pretty cool. The green LED on the front indicates that it is getting power, and the red LED indicates that the relay is "switched". (In our case, red light means the pump is pumping!) The top two dials set the amount of time, and the bottom dial is the "mode". You will need a very small screwdriver to set it. There is a very small arrow on the dial that is a bit difficult to see.

The mode we want in our case is "H", which basically means "when the button is pressed, the relay will turn on for the set amount of time... if the button is pressed again before the end of the cycle, it ignores it, the additional button presses will not affect the total amount of time it runs".

The other two dials are to set the amount of time it runs. On the top dial, you can choose between 1 second, 10 seconds, 1 minute, 10 minutes, 1 hour, 10 hours, 1 day, 10 days, ON, and OFF. The second dial is the percent of the top dial.

For example, if you wanted it to be on for 30 seconds, you could choose 1 minute and 50%. If you wanted it to be on for 3 minutes, you could choose 10 minutes and 30%. If you only needed 10 seconds you could choose 10 seconds and 100%.

To find what you should set your timer to, I turned on the hot water and timed how long it took to get hot. I then set that time into the timer/relay. The pump may or may not move the water at the same rate as it would "naturally", but it's a great starting point. Try it out and adjust as you need. My final setting ended up being 10 minutes and around 13%, about a minute and 15 seconds.

No more dilemma between cold hands and wasted water! Enjoy!