Commercial applications continue to include domestic hot-water return or recirculation lines as a best practice. Over the past few years, DHWR lines have become popular in residential applications as well.

Adding a return line to the domestic hot-water system creates a closed-loop path that allows the water to circulate back to the water-heating source to keep the lines warm when fixtures and other loads are not in use. DHWR piping provides hot water to the various loads in the system very quickly upon demand — even if the hot water has not been required for a long period of time.