Watts Premier Hot Water Recirculation System
According to Watts, the Premier Recirculating System provides instant hot water in all water taps. The Watts Premiers DHW Drain Pump delivers comfort and home savings so you can use hot water at all times when you need it. "
Technically, this is not really true …  A Hot Hot Water Circulation System
The Watts Premier system is what I like to call a hot water circulation system.The system includes a valve under the sink, and the pump in the water heater. The pump creates a differential pressure between the hot mixer and the cold faucet
The valve connects hot and cold taps and when the temperature drops below 98 °, water flows through the valve, faucet / valve
When the valve detects a temperature above 98 °, the valve closes and the flow stops, in other words, it works in the same way as a conventional temperature controlled circulating system, unless hot water is circulated instead of hot, and of course uses the cold water line as a return line  Energy Consumption
Water can not be hot, but much m is more efficient than without the premier system, so the water heater needs to consume more energy to keep the water in the big heat exchanger in which you are calling a hot water pipe.
One of the great things about Watts pump is that you can put a valve under each sink if you want, and you get hot water for any or all of the fittings. It also increases the system's power consumption.
Does not Work with Tankless Water Heater
The pump is very small and does not consume much energy, yet does not pump much water either. It is unlikely that Watts Premier will be able to turn on a little water tank without a tank. According to the pump diagrams on the Watts website, the pump shut-off pressure is approx. 1.5 psi.
Watt uses a Grundfos UP15-10SU7 / TLC pump with a 1/25 horsepower engine that consumes 25 watts. The pump runs continuously, so running 16 hours a day is 25 watts per hour x 16 hours per day x 365 days per year = 146 000 watts per hour per year in energy consumption. It's 146 kWh, and for example 13 cents / kWh would be $ 19.00 a year. This would be considerably smaller than the energy lost due to circulated hot water.
Hot water naturally gets faster, as if the pipes could cool down because they would be cooler, cold water while flowing to the tap. But this is definitely not called "Instant."
The Watts Premier System website price is $ 225.00
The Metlund Dome Mandator
The Metlund D & G system is a demand type hot water system. Just pushing a button pumps the water into the luminaire when it "requires". The D & D pump is under the sink and connects to hot and cold water valves such as a Watt valve. A power supply is required to insert the pump.
When the button is pressed, the pump starts pumping the water into the valve and returns the chilled water through the hot water pipes through the cold water pipes to the boiler. When the pump suddenly detects a temperature drop, the hot water does not enter the cold water line
Since all the pumps have filled the piping hot between the appliance and the boiler as well as the operation of the faucet you will not be able to use any additional energy from the heater. As the pump runs for a very short time, it uses less power than the Watts pump, with approx. $ 1.00
Works with All Tankless Water Heater
Some models work with tankless water heaters. Because tank water heaters typically take water for longer than 10-20 seconds, the Metlund pump is a very pleasant addition to any water tank, gas or electric appliance without tank. Hot water can not be punished very quickly and with energy, and it saves a lot of water.
Metlund pump models cost about $ 350 to $ 750
Source by sbobet