Hot water pipes that are extended any great distance to a fixture or group of fixtures should be provided with a circulation pipe through which hot water can circulate and thus be close to the faucets at all times. If circulation pipes are not provided, the water in hot water pipes cools when not being constantly drawn, and much time is wasted emptying the pipes of cold water when hot water is wanted. The water annually wasted in this manner, in any building, would more than pay for circulation pipes.

When installing the hot water system, a return pipe of smaller diameter than the hot water pipe is carried from the highest point of the hot water riser back to the boiler where it may be connected to a separate tapping in the boiler or it may be connected to the return pipe from boiler to waterback. In large buildings return circulation pipes are connected into a return header or manifold close to the hot water manifold. A valve should be put in each return pipe in a position to correspond with the shut-off valve in a hot water pipe, and both should be opened or closed as the case may be. Should only the hot water valve be closed, water would back up through the circulation pipe, and should the return valve be closed there would be no circulation through the pipes.