Hot Water Pumps - Circulating, Recirculating, and Recirc Systems - What Are They and How Do They Work?
How hot water circulating systems, often called recirculating systems or recirc systems and pumps, work, and the benefits and problems they may have with energy efficiency and water savings.
Hot Water Pumps, Circulating Systems, Recirc Systems and pumps - What Are They and How Do They Work?
Traditional hot water circulating systems use a hot water circulating pump to pump hot water from the water heater, through the hot water piping, and on back to the water heater through an additional length of pipe that runs from the furthest fixture back to the water heater. This provides you with instant hot water.
Circulating systems can waste lots of energy
This type of hot water circulating system provides nearly instant hot water at the fixtures, but wastes a tremendous amount of energy through both the energy required to operate the hot water pump and even more heat energy lost from the piping.
Timer and temperature controlled circulating systems
Several methods have been employed to reduce the energy waste associated with hot water pump circulating systems. Timers are sometimes placed on the circulating pump so the system shuts the hot water pump off during hours that one one normally uses hot water such as from midnight to 6:00 a. m.
Sometimes the circulating pump is controlled by a temperature sensing circuit that shuts the hot water pump off once the water temperature reaches a pre-set temperature such as 140 degrees and then starts the pump back up when the water temperature in the pipe drops below a second set point such as 110 degrees.
This type of system does little to reduce the energy losses because the lower set point is still high enough to cause continual large heat losses from the system, and the pump does not contribute nearly as much to the loss as the heat loss itself.
Circulating pumps have little power and low flow rates
Circulating, or recirc pumps have a very small motor typically 1/120 to 1/20 horsepower. The can't produce much head (pressure) and as a result, end up with very low flow rates. Most circulating pumps will not even turn on a tankless water heater.
Hot water circulating pumps such as those made my Taco Pump company and Grundfos, and others are not green products at least when used in traditional type circulating systems.
Greener water conservation products, hot water demand systems save water and don't waste energy
The greener alternative, hot water demand pumps such as the Chilipepper CP6000 and the Metlund D'mand system use very little pumping energy and since they don't actually circulate the hot water they do not add any energy loss to a typical hot water usage.
Demand systems only run for a few seconds until the hot water reaches the fixture and then shut off, so the electricity used for pumping amounts to less than $2 per year. Hot water demand systems are truly green products for water conservation.
Diagram of a hot water circulating system including fixtures, pump, check valve and water heater.