The benefits of hot water recirculation are rather obvious. You get nearly instant hot water, which is convenient, and you save a substantial amount of water (up to 17,000 gallons of fresh water annually for the average household) and aid in preventing pipe freezing in cold weather. But there are a few other issues to consider.
There are a number of types of recirculation systems for residential plumbing. Traditional, circulating pump type systems pump hot water through the piping from the heater to the fixtures and back to the inlet of the heater. These hot water recirculation pumps are wasteful of energy. In addition to the energy wasted by the pump, the large volume of water requires your water heater to expend more energy to replace the constant heat loss being radiated from the piping system. These systems or expensive to install and often must be installed during the construction stage of the home. In years past when energy was cheap and plentiful these systems were very popular, however, in today’s energy conscious environment they are becoming rare in residential plumbing systems.
There are ways to reduce the energy loss such as putting the pump on a timer to reduce the number of hours it runs. The downside to this is that if you want hot water when the system is off, you will have a long wait and you will still run a lot of water down the drain while waiting for the water to run hot. These type of systems are also somewhat difficult to install (requiring plumbing alterations and electrical wiring).
Another type of hot water recirculation are “demand” pumps. The demand pump only recirculates the water back to your water heater when you push the start button. The downside is you must push the button 15-20 seconds before you desire the hot water and they require a start button wired at each sink or shower. These type of systems although efficient for saving water are also difficult to install (requiring plumbing alterations, start buttons and electrical wiring).
And finally innovative new technology brings a hot water recirculation system that saves water, saves energy, is convenient to use and easy to install (not requiring pipe cutting or electrical wiring). This system is typically used on retrofits but may also be installed on new construction. It consists of a temperature controlled thermal convection powered hot water recirculation valve installed under the plumbing fixture farthest from the water heater. The system contains a sensor, which opens the valve when the water temperature drops below the adjustable temperature setting.