There are two types of recirculation system that can be installed in homes.
1. Dedicated Recirculation Loop: This is also known as an open loop system since the recirculation pipe is open all the way around. This type of system has a 3/4″ hot water line that leaves the water heater, runs throughout the house within 6′ of each hot water fixture where a 1/2″ line Tee’s off to feed the fixture and then returns to the water heater, goes through a pump, a check valve and then Tee’s into the cold water supply feeding the water heater. Sometimes, with tank water heaters, they are instead fed into the tank drain. Many times the return line is necked down to 1/2″ pipe after the last water fixture to save money on installation cost, but we recommend that you keep it at 3/4″ if you are installing it new as you will get faster recirculation and therefore quicker response time at the faucet which is important when using our controllers to run the pump on demand.
We have seen houses that have been plumbed with a recirculation line but the line was never hooked up. If this is the case you will see a short copper stub sticking out of the wall in the vicinity of the water heater that is capped off.
The dedicated recirculation loop requires a third pipe coming back to the water heater so if you only see the cold water feed going into the water heater and the hot water line coming out of the water heater you do not have a dedicated recirculation loop.
2. Non-dedicated Recirculation System: This is also known as a closed loop system since it uses thermostatic valves that are installed underneath the sink(s) at the furthest location from the water heater which connect the hot water line to the cold water line. When they are cold they allow water to flow from the hot water line into the cold water line effectively using the cold water line as the recirculation line. However, once hot water reaches the valves they close preventing further flow hence the name closed loop system. These systems also require a pump at the water heater, but the difference is the pump is installed on either the inlet or the outlet of the water heater rather than on a dedicated third water line. The purpose of the pump in these systems is to push the hot water from the water heater out through the hot water line pushing the cold water in the line through the thermostatic valve and into the cold water line. When hot water reaches the thermostatic valve the valve closes preventing further flow. Our controllers recognize that the valve has closed because the flow has stopped and turn the pump off. All other systems run on a timer and will simply dead-head against the closed valve.
This system requires the installation of the thermostatic valve underneath one or more sinks at the furthest location(s) from the water heater. If you don’t see any sort of metal or plastic valve underneath any sinks in your home and there is no pump on the inlet or outlet of the water heater you do not have a closed loop recirculation system installed.
These systems work well when there is no other option but they have a couple of disadvantages.
These are really only problems at the fixture where the thermostatic valve is installed as other fixtures that are on the same line closer to the water heater will have hotter water and will not have warm water in the cold water line.
We always recommend installing a dedicated return line if it is reasonable to do so. Older, multi-story homes don’t lend themselves to adding a recirculation loop unless you are in the process of a full remodel. However, if you have a single story ranch style house with the plumbing running underneath the house or in the ceiling of the basement, then running a return line can be very straightforward especially with the advent of PEX plumbing line. You simply go to the furthest water fixture in the home, cut the hot water line and insert a Tee. Then run the PEX line from the Tee back to the water heater. Doing this in PEX eliminates any need to sweat copper piping but does require a specialized crimping tool.
If you have a dedicated recirculation loop you would need the Smart Recirculation Control 32 with a pump.