The principle is that a pump is installed under the sink that pulls hot water up to the pump, and returns it back down the cold water pipe to the water heater at the press of a button. The 54 Watt pump shuts off as soon as sufficiently hot water is present. Each time you need hot water you just press a button and wait half a minute while the water is sent back to the water heater tank instead of down the drain. The pump shuts off at a pre-set temperature.
This system differs from other designs that constantly circulate hot water through the plumbing to keep it available at all the faucets constantly. I don't recommend that type of system as it actually wastes energy, both at the pump and due to radiated heat loss from the plumbing which acts as a defacto radiator in the walls of your house.
The D'Mand system reduces waste and saves energy in 3 ways:
- reduces the use of our 1500 Watt 240Volt well pump.
- reduces the need to heat water that would just go to waste down the drain.
- reduces waste water entering our septic system.
The installation of the pump is quite simple. After shutting off the water supply and draining the lines to the sink, the faucet shut offs are removed. A tee is inserted, and the shut-off is replaced. Then the 2 flexible lines to the pump are installed onto the new tee thread. This took me about 20 minutes.
I am an experienced plumber so I had no trouble installing the pump. Any plumber would also find this a simple installation.
The challenging part is that an electric outlet is required under the sink. The nearest outlet in our bathroom is off to the right. So I made a run to the hardware store to get a bunch of Wiremold (surface wiring conduit) parts. Then I added a breakout box on top of the existing outlet and ran Wiremold channel across and down into the space under the sink where I installed a new outlet for the pump. This part took over 3 hours!
I also made an attractive circular white acrylic switch plate, and used a stainless steel push button.
Once the button is pressed the pump turns on immediately and shuts off automatically as soon as it senses hot water at the pump. This saves several gallons of water that would otherwise run down the drain, and reduces the usage of our tankless water heater. In our home the cold line returns to the bottom our solar storage tank where the sun heats it up for free.
Before the pump was installed it would take 80 seconds for the hot water to arrive, now the pump brings it up in about 50 seconds after pressing the button, and the water runs hot from the faucet within a few seconds. They also make a motion sensor that will turn the pump on automatically when you enter the bathroom (or kitchen). Here is the accessories page.
This system is relatively expensive and I don't expect a payback any time soon. This is something I did as part of my commitment to living sustainably using technology. I admit it may not be for everyone.