Plumbing glossary

Hot Water Recirculation

Hot water recirculation (also called a hot water recirculating system or instant hot water pump) is a system that keeps hot water continuously moving through the hot water supply pipes so that hot water is immediately available at every fixture in the home — no more waiting 30–90 seconds for the tap to warm up, and no more wasting cold water down the drain while you wait.

How recirculation systems work

A small circulation pump (typically installed at the water heater) continuously circulates hot water from the heater through the hot water supply piping and returns it to the heater via either a dedicated return line or the cold water line (with a bypass valve at the farthest fixture). Water that has cooled in the pipes is constantly pushed back to the heater before it reaches the tap.

Types of recirculation systems

Full system with dedicated return line: the most effective — a separate ¾" return pipe runs from each fixture group back to the water heater. Fastest response time, highest upfront cost (new construction or remodel).
Retrofit comfort system (crossover valve): uses the cold water line as a return by installing a temperature-actuated bypass valve under the farthest sink and a pump at the water heater. No new piping — works with existing supply lines. Minor crossover of warm water into cold line (slight lukewarm cold water briefly after the pump runs).
On-demand recirculation: pump activates via a push button, motion sensor, or smart home trigger rather than running continuously. Reduces energy use versus always-on systems; slight delay (10–30 seconds) vs. instantaneous.

Energy tradeoff

Always-on recirculation systems maintain heat in piping constantly — running 24/7 increases water heating energy by 15–30%. A timer or on-demand activation reduces this significantly. Insulating the hot water piping is an important companion measure.

Cost

A retrofit comfort pump system costs $150–$300 for the pump; $250–$600 installed. A full dedicated-return system during new construction adds $500–$2,000 to plumbing costs depending on home size.