A different take on hot water recirculation

Snackchaser · February 10

This is yet another modification for instant hot water. I was inspired by @Minnesota Oli who brilliantly installed a timed solenoid valve to circulate hot water from the bathroom faucet back to the freshwater tank. This saves from wasting water down the drain while waiting for it to get hot. I loved the concept of using a timer, but I went with a recirculating pump instead of a solenoid valve. We’ve used this design for about a year now, and it’s been very luxurious and effective. Not only does it help conserve fresh water, it prolongs the grey water tank volume which is now our most limiting factor when boondocking.

The recirculation pump is started from momentary push button switches installed at each faucet. The button(s) activate a timer/relay that runs the pump for 25 seconds. Experimentation showed that 25 seconds sufficiently heats the pipes to deliver hot water at full temperature. The pump circulates the hot water back to the hot water heater, rather than into the fresh water tank.

The new recirculation pump is the same model as the existing main pump. It was connected with flexible faucet hoses to reduce vibration and isolation valves so it can be used as a spare if needed. The pump was mounted on a plywood board fastened with construction glue to the vertical fiberglass surface by the furnace return vent.

Note: Pump pressures can vary, so it might be necessary to slightly adjust the pump pressure switch to overcome the house pump pressure. Also, the pump may not overcome some of the higher city water pressures if a pressure regulator isn’t used. . . as it should be regardless.

The Oliver has two separate hot water loops that I joined together so that the kitchen faucet is included in the recirculation loop. Being a shorter loop, there was less water wasted while waiting for it to get hot, but it's used more frequently so it's worth it to join the loops. There is plenty of room under the floor and behind the cabinets to run PEX return lines. “T” fittings were installed at the kitchen and bathroom faucets, and at the water heater input as shown on the drawing.

Note: There was a buried 3-way valve, flexible by-pass hose, and a (clogged open) check-valve for water heater isolation. It was restricting flow and pinching the furnace duct so I completely removed it. The Water Heater can be easily isolated other ways if the need arises.

The momentary push buttons were arbitrarily programed so that they must be depressed for one second before the pump will start. The buttons were non-intrusively mounted in 1/2” holes. The bathroom button is behind the existing bathroom pump switch, the kitchen button is above the sink, and the outdoor shower button is inside the shower wand enclosure. The sheathed button wiring is joined together under the street side bed along with the timer. I used terminal blocks, but wiring could be joined with any number of splicing methods. The button wiring carries no measurable voltage or current, it’s simply a switch to “low” (ground) for the timer trigger. Wire runs to the bathroom and outdoor shower switches are pretty straight forward, the bathroom vanity shelf needs to be removed for access. The kitchen switch wiring is laid under the liners in the upper cabinet, through the attic, and down the rear wall next to the clear AC drain tubing.

I used a programmable timer/relay for the pump. An inexpensive (re-usable) Programer is also needed to program the timer. The Programer has built in App and Bluetooth for programing it on a smart phone and I’ve provided a screen shot of the program settings. This is truly simple to do, and quite fun!

As many in this forum know, the Tuma Comfort II water heaters have a built-in circulation pump, controlled by temperature sensors, that keeps a small internal tank ready with hot water. Only one part (unavailable to public) differentiates it from the Truma Comfort II “Plus” that has a full hot water recirculating system. It took a few years, but I finally have the design details for that part and I’ll try to fabricate one when the Truma is removed for the up-coming factory recall work. More to come if I’m successful.

The Truma “Plus” recirculation system provides true instant hot water (when not in Eco mode) because it keeps hot water circulating through the system based on temperature sensors. My system has a 25 second delay before the water is hot, then it cools down until the button is pushed again. This is less convenient, but more energy efficient because it doesn’t periodically cycle. I’m still on the fence which system is better, but fortunately the recirculation loop installed in this modification will work for both systems.

Hope someone finds this useful!

Cheers! Geoff

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