Hot Water Circulating Pump: How Does It Work

How Circulation Pumps Work

For the purposes of this article circulation pumps, otherwise known as circulators, are used in 2 different ways. One way the pump runs all the time. This strategy is used with a dedicated line.

The other way is to only run the pump when there is a demand for hot water. This strategy is used with either a dedicated line or to push cool water back to the heater through the cold line.

What is a dedicated hot water line?

The following terms are used to describe a dedicated line:

  • circulation loop
  • circulation line
  • recirc loop
  • recirc line
  • return line

All of these terms refer to a water line that runs from the heater out to all the fixtures in the house and then returns to the heater.


  1. Hot water is virtually instant


  1. The water loses heat as it travels through the house and must be heated up again
  2. Studies show that people only use hot water 5% of the time yet the line is hot all the time – high waste of energy
  3. Most leaks happen in the hot lines with circulation pumps

How can the cold line be used to move cool water back to the heater?

If a circulation pump is installed on or near a heater on the hot line out in to the house and a bridge valve, or crossover valve, is under the farthest fixture a continuous loop is established.

Hot and cold water are pressure balanced in a home. The pump helps the hot side overcome the cold side.

Once hot water reaches the bridge valve the valve closes so that no more water can be pushed into the cold line and the pump shuts off.


If a home has a dedicated hot water line they will get almost instant hot water with the circulation pump running all the time. Although this is convenient it is very wasteful. Water bill is low – energy bill is high!

Without a dedicated line water will be wasted down the drain unless there is a circulation pump installed. Without the pump water bills are high. With it water bills are much lower.

There are conversion kits on the market to convert a continuously running pump in to a true on-demand pump. And there are several systems for homes that do not have a dedicated line.

Timers are always a bad choice because they waste energy and put unneeded added pressure on your plumbing fixtures.

By adding a circulation pump to a plumbing system without a dedicated line a lot of water will be saved.

By adding a pump manager or controller to pumps in a dedicated line energy will be saved.