I’ll answer this 6 years late for those who are wondering. The pump is needed to cycle the water through the closed system. When the system is closed, the water has nowhere to go that has lower pressure (i.e. the tap) so it wouldn’t move without the pump. The pump pushes the previously hot water back into the cold side near the tap, bringing hot up to the tap.
I figured this would be an issue when I installed my system several years ago. My plumbing is under the house and easily accessed, so I ran a dedicated return line back to the water heater. There is no wait for hot or cold at any of the taps. Well worth it. Will be installing the same setup this week for my sister. Using pex this time so install should be quick.
can i use this on my tankless water heater and install it under sink
depends on what your goal is!! if you are wanting to keep the cold water line feed warmer for a non freeze in cold areas of the country.. then yes!! if you are trying to keep the water in the tank from freezing... you are better off using a surface tank heater on the outside of the tank to keep the tank warm... I have seen these pumps used in several cool systems that they were not designed for!!
Yes. The motor is installed at the hot side of the tank and the sensor is installed at your farthest sink or where you want almost instant hot water. I have mine running all the time, as my plumbing is in the concrete foundation. Love it!
No, the manifold allows for the return through the cold water line.
Watts web site shows the operation cost at less than 5 cents per day. Or if you Google search and find out the power usage of this pump in KW (kilowatts), then you can use your electrical cost in your area (from your electrical bill) to calculate the cost per day. Should be very low.
Nope you just need 1 unit of the entire house you place the valve on the furthest bathroom sink from the heater.
Does the pump affect the water flow to faucet when pump is not running?
I'm not sure it will add value or increase performance. This pump should be placed at the FURTHEST faucet location (from your water heater). It then will circulate hot water throughout the ENTIRE hot water loop in your home.