Hot Water Recirculation Systems

By Kenton Shepard

Hot Water Re-circulation Systems

When a hot water valve is opened in a home, the water in the hot water pipe has usually been sitting in the pipe for a while and is no longer hot. Anyone needing hot water opens the hot water valve and waits until hot water from the water heater tank reaches the fixture. In large homes, especially at the plumbing fixtures farthest from the water heater, this can take a while and the water running in the meantime is wasted.

Hot water recirculation systems circulate water in the hot water pipes, so that hot water will always be available and less water is wasted. This causes the water heater to run more, but how much more depends on the type of system. If the home uses a solar water heating system, this is less of a concern, since heating water is inexpensive or free.

Undersink System

This systems is typically used on retrofits but may also be installed on new construction. This pump is installed under the bathroom sink farthest from the water heater. The pump contains a sensor which switches the pump on when water temperature drops below 85°F and switches it off when water temperature reaches 95 °F. Newer pumps are adjustable from 77° to 104°.

In this system hot water is re-circulated intermittently. Hot water is returned to the water heater via the cold water pipes. This raises the temperature of the cold water slightly, but it returns to the usual cold temperature in a short time.

Source

This diagram shows one undersink re-circulation system.

Inspectors will recognize this system by the pump installed under the sink farthest from the water heater. The inspection is limited to proper operation.

Constant Circulation

This system is more common in newer homes. In the constant circulation system, instead of terminating at the plumbing fixture farthest from the water heater, the hot water pipe returns to the water heater, forming a loop. This loop usually returns at the drain, which is removed. A circulation pump is installed in-line and hot water is constantly circulated so that hot water is instantly available at each hot water valve. 

Source: Kenton Shepard

The hot water pipe can be seen returning to the water heater at the tank drain . The circulation pump was unplugged  and the pump is mounted on the wall.

Inspection Considerations

These systems all require an in-line air valve and shut-off. Other requirements will vary with the install configuration but may include a check valve, hose bib and an additional shut-off. Inspectors will recognize these systems by the circulation pump installed.

Limit inspections to proper operation.