The notion of a hot water "recirculator" sounds pretty good on paper: less water used waiting for hot water to reach the tap, potential for less energy used for water heating, and relatively inexpensive to buy and install. Some localities have even implemented rebate programs for installing one of these devices as they have been shown to help conserve water.
While there are variations among designs, the basic operation consists of some way of returning cold water to the heat source until the temperature reaches a set level or alternately, keep hot water lines in the home filled with water at a set temperature.
So far, detailed third-party analysis of the savings obtained from these devices seems to be lacking. Water conservation seems the biggest return among users - not so much on the energy side. Without some hard data comparing different systems it's difficult to make a clear recommendation, but it seems reasonable that there are situations where the devices will come in handy and achieve some savings. Following are some pluses and minuses that you may want to consider:
- Reduces wait time for hot water at your tap
- "Unused" cold water not simply going down the drain, reduces waste
- Possibility for saving money on utility bills (should evaluate as a combination of water, gas, and electric usage)
- Some devices may not be usable or effective in certain situations (such as coupled with a tankless water heater)
- Some devices target only a specific location or faucet, not for the whole house
- May require installation of additional electric outlets adding to overall cost
- Other plumbing options may be available that are more cost-effective
For more information, check out these websites:
- Demo and installation of pump attached to water heater (Lowe's product demo)
- Homeowner's experience with recirculation vs. tankless and solar
- Detailed analysis of a particular type of system at Oak Ridge National Laboratory
- Toolbase overview of hot water recirculator