Hot water reticulation loop (Ring-main) basics by the ITS Heat Pumps & Solar technical team.
Do you hate waiting for your shower to warm up in the morning?
A common way to avoid this is to install a hot water ring-main. This type of system works by circulating hot water around your house to minimise the amount of waiting time and water wasted when you open a tap.
Consider an ordinary hot water system. You’ll have a hot water cylinder somewhere in your house. If you have a large home, the distance between your water heater and your bathroom might be quite a long way.
When you open a hot tap, water has to run from your water heater all the way down to the tap. If the pipes are cold, it will cause the water to cool down along the way so you’ll have cold water coming out of the hot tap until all the pipes have warmed up between your water heater and your tap.
The ring-main solution has a small return pipe installed with allow water to flow back to the water heater. A circulating pump keeps the hot water moving slowly around the system, so that hot water is always available within a couple of metres of each hot water fixture.
The pump is controlled by a thermostat attached to the hot water return pipe. This turns the circulating pump on when the pipe cools down.
The only drawback with a hot water ring-main system is that the pipe thermal losses will increase. This increases your water heating costs. But, if the pipes are properly insulated and you are using a very efficient heat source like a heat pump, this increase is minimal.
If properly designed and installed, a hot water ring-main will provide you with hot water on tap almost instantly, which is essential especially in larger and more up-market homes.
Key components of a ring-main system
The below diagram shows a basic hot water storage tanks system with a ring-main.

The key components are:
Using a heat pump to heat your hot water storage tank will typically result in an average electrical heating cost saving of more than 60%. With the higher piping thermal losses associated with a ring-main, it makes even more sense to use a heat pump to do the tank heating.
A “poor man’s” ring-main
In most cases ring-mains are in bigger houses with higher water consumption and so the typical system starts at 300L or more. The smallest proper ring-main tank we supply is the Reflex 500L form Winkelmann in Germany. We often get clients that want a ring-main but do not want to replace their hot water storage tank with the correct type of tank. In most cases this can be made to work but it will always give inferior performance compared to using the correct equipment for the job. Below is an example of how two standard horizontal 200L geysers with a heat pump as the heat source can be plumbed to connect a ring-main.

A “poor man’s” ring-main
As mentioned, the above is a compromise. It is not the correct tanks for the job and so the following must be noted:
- The hot water stratification in tank 2 will be disturbed by the ring-main. So, if for example the above tanks are 200L each, you will only be able to draw about 250L out of the system at a time under certain draw-off profiles, and not 400L.
- The ring pump must be temperature controller by a controller like the SR81. This will greatly reduce the stratification disturbance/ heat pump loading disturbance and it will reduce energy consumption. The pump must be set to the lowest speed required.
- Variants of the above that we have seen includes bringing the ring back on tank 2, or on the cold inlet of tank 1. This will introduce more problems and should be avoided.
- The heat pump must be installed using the ITS patented loading valve technique. Due to the flow restriction caused by the tanks in series etc., the loading valve must be an LK821 of the correct size, and not a LK550.
- The heat pump size will be based not only on the number of liters of hot water required per day, but also on the length of the ring main and quality of the ring insulation.
- Any difference on the actual port positions compared to the above example can have a drastic impact
on performance.
For more information on this topic and help with system design, please feel free to contact our technical department and we will gladly assist.