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Keeping Hot Water Hot

How do they do it? 

Nicole Imeson

Have you ever stayed at a hotel and turned the shower on to find only cold water? Or perhaps you live in an  complex and have experienced several leaks on your piping systems? 

Potable hot and cold water is piped to all of the plumbing fixtures in a building to provide water for tasks like hand washing, cooking, showering, or laundry. When the plumbing fixtures are not in use, the hot water slowly cools down, becoming cold water. This means you have to run the water for several minutes for it to get hot again. 

Not only is this time consuming, but it’s also a waste of water, often leading to higher utility bills and an increased impact on water scarcity. However, by installing a recirculation system, you can ensure the hot water is ready when you need it. 

A potable hot water recirculation system includes a small pump and additional piping to provide continuous flow through the hot water system, even when no fixtures are in use. The system circulates the warm water back to the central plant to be reheated and redelivered to the plumbing fixtures on a continuous basis, preventing the water from getting cold. But even hot water recirculation systems are not free from problems. 

There are two common issues that plague these systems, and both are related to flow. When the water flow is too low, or the recirculation pump is too small, the hot water at the plumbing fixtures furthest from the hot water plant may not circulate back to the central plant to be reheated. This means that water becomes cold until the fixture is used, wasting time and water.

Conversely, when the water flow is too high, or the recirculation pump is too large, there is potential for increased wear and premature failure of the hot water piping system. The potable water system is an open system - meaning that water comes in from the municipal service and flows out through fixture drains.  It doesn’t recirculate the same water around and around like you would in a hydronic heating system, which circulates heated water in a closed loop to heat various spaces in a building without introducing new water to the system. Instead, in a potable water system, air bubbles are introduced into the system from the municipal service. These air bubbles, when traveling at a high velocity, start to erode the inside of copper pipes and create a phenomenon called ‘pitting’. Over time, this pitting will create pinhole leaks in the pipe and wreak havoc on your building finishes, such as drywall or lighting.

While these issues appear to oppose each other and present different symptoms, the solution to either issue is the same: system balancing. System balancing is the addition of flow control devices, commonly called balance valves, to limit the water in a system to a specific, predetermined flow rate. By installing balance valves throughout the potable hot water recirculation system, you can ensure that water flows equally at each fixture, and you have hot water when you need it, without the risk of premature piping wear. 

If you think you need a recirculation system in your building or home, speak to a professional to review your specific system and determine the piping distribution and sizing, pump size and system flow rates.

Author bio: Nicole Imeson is a mechanical engineer in Calgary, Alberta. She has spent her career overseeing the construction of plumbing, HVAC and fire protection systems in various facilities across Western Canada. In her spare time, Nicole hosts a podcast about engineering failures called Failurology.
Social media: TW: @failurology LI: @FailurologyPodcast