The benefits of hot water recirculation systems are rather obvious. You get nearly instant hot water, which is convenient, and you save a substantial amount of water. But there are a few other issues to consider.
There are a number of types of recirculation systems for residential plumbing. There are the traditional full-time circulating systems that continuously pump a small flow of hot water through the piping from the heater to the fixtures and back to the inlet of the heater. Besides being quite difficult to install (requiring and electrical outlet under your sink), these full-time hot water recirculation pumps are very wasteful of energy. Your water heater will have to work much harder to supply the heat needed to replace the heat being radiated from the piping system. 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 using a demand button or putting the pump on a timer to reduce the number of hours it runs. The drawback to this is that if you want hot water at a different sink or the system is between cycles, you will still have a long wait and run a lot of water down the drain to get hot water. Several manufacturers like RedyTemp, Grundfos, Laing, Metlund, Taco, Chilipepper, and Watts offer these type systems.
Temperature Controlled Thermal Convection Powered Instant Hot Water Valves SAVE WATER and SAVE ENERGY! This is the most energy efficient type of recirculating system. It only operates when needed and is a simple DIY installation (requiring to electrical connections). Only one manufacturer offers this patented technology. The Hot Water Lobster Instant Hot Water Valve.Install a temperature controlled hot water recirculation valve, which provides instant hot water (so water is not wasted down the drain waiting for water to run hot at your faucet or shower). This simple DIY installation can save an average household up to 17,000 gallons per year. It also saves energy costs and can prevent pipe freezing.