How FlowGuard Gold CPVC and PEX Perform in Hot Water Recirculation Systems
Contractors | Multi-Family | engineers | residential plumbing | CPVC
Hot water recirculation is a popular feature in many multi-family developments and is becoming more common in single-family new construction. With a hot water recirculation system, unused hot water is recirculated back to the water heater, rather than remaining in the pipes to cool. As a result, these systems can reduce the energy required to heat water while making hot water available faster at fixtures.
The Basics of Hot Water Recirculation
Hot water recirculation systems can use a standard trunk-and-branch system design with a return line from the last fixture back to the water heater. System designs that use a remote manifold can also be adapted to support hot water recirculation with a return line from each fixture running back to a return manifold. Most systems include a pump at the water heater entry to keep water circulating continuously or periodically based on time or demand.
Energy savings can be realized because water is entering the heater at a higher temperature and so requires less energy to heat. For example, without a recirculating system, the temperature of the water entering the water heater will typically be between 50° F to 60° F depending on the time of year and location. With the recirculation system, the temperature of water entering the water heater will be in the 80° F to 100° F range, or even higher, depending on the size and design of the system. According to the U.S. Department of Energy, water heating accounts for 14-18% of utility bills in the typical home, so improving efficiency in this process can yield meaningful savings.
In addition, these systems can reduce water consumption because they enable hot water to be delivered to fixtures faster, minimizing the amount of water that goes down the drain while residents wait for hot water to reach fixtures.
PEX Velocity Limitations in Hot Water Recirculation Systems
When installing a hot water recirculation system, it’s important to understand the impact certain materials can have on system sizing and design.
If using PEX, be aware of the material’s water velocity limitations in this application. PEX manufacturers and some model codes limit water velocities in PEX to 2 feet per second in hot water recirculating systems. That can dramatically reduce flow rates across the system and typically requires upsizing the piping to manage velocity while still providing adequate volume. While the reason for this limitation has not been disclosed by manufacturers, some data suggests that PEX vulnerability to chlorine degradation may be made worse by turbulent, fast moving hot, chlorinated water.
Some PEX manufacturers limit velocity for the whole system and some for only parts of the system so there is disagreement in the industry around how to properly account for this risk. However, every manufacturer imposes velocity limitations in at least some part of a hot water recirculating system, and the resulting need for upsizing should be factored into project costs when using PEX.
Using FlowGuard Gold for Hot Water Recirculation System
FlowGuard Gold CPVC is immune to degradation from chlorinated drinking water and has no special restrictions for velocity in a hot water recirculation system, eliminating the need for upsizing. The FlowGuard MultiPort CPVC mini-manifold can also enhance cost-efficiency in hot water recirculation designs using mini-manifolds. The pipes and fittings used for a PEX mini-manifold system can cost as much as double the equivalent FlowGuard Gold CPVC system.
When using CPVC in a hot water recirculation system, use a metal-body mixing valve instead of a tee fitting to incorporate the hot water return back into the cold water line, CPVC fittings are not designed to be used as a mixing device. Alternately, the hot water return can be piped directly back into the water heater through a dedicated return port, or the line can be piped into the drain valve.
Also, as with any plumbing system, be sure to account for expansion and contraction by ensuring the natural movement of the pipe is not restricted and there is adequate spacing between elbows and hangers.
Eliminate Upsizing Costs with FlowGuard Gold CPVC
When properly designed, hot water recirculation systems can create energy and water savings for the building owner and/or residents. But with PEX they can also add to project costs because larger size pipe will be required to maintain adequate water volume at low velocity. FlowGuard Gold CPVC’s immunity to degradation from chlorinated drinking water eliminates the need for upsizing, and with installation times 15% faster than PEX in trunk-and-branch configurations, enables superior performance at a lower installed cost. Download our submittal specifications to learn more.
