The value of hot water secondary return to improve the hot water experience

July 20, 2023

As our homes get bigger, one of the biggest issues is delivering hot water quickly and efficiently to our hot water taps. Longer pipe runs means the hot water cools. When the outlet is turned on, then all that cold water has to dissipate before the hot water arrives.

We know Mixergy hot water cylinders can heat water faster than your traditional cylinder. But did you know that the configuration of the pipe set up in the home also impacts how quickly and efficiently the hot water gets to the taps?

To ensure hot water is delivered quickly, most people will locate their hot water cylinder centrally within the home, between the hot water outlets, which reduces the required pipe lengths.

However, when this is not possible, you can also set up a hot water return circulation loop from the cylinder itself. This can significantly reduce the time it takes for hot water to get to the taps.

It should also be noted, that although not a legal requirement, the HSE recommends hot water should be delivered at 50ºC within 1 minute to help combat legionnaires disease.

So let’s take a look at how Mixergy is the ideal cylinder solution in a hot water secondary return system.

How does a secondary return system work?

The idea is you have your primary hot water pipe flowing through the house. Next to this, you’d then have a “secondary recirculation pipe”, which travels beside the hot water primary pipe to the extremities of the system.

The secondary pipe taps into the primary to join the two pipes together. The cylinder then has a hot water circulation pump. The pump is set to push the water through the primary pipe to the tap, and it then returns via the secondary pipe, keeping your hot water hot all the way to the tap.

The pipework configuration needed

Historically the hot water secondary return pipework configuration would be similar to the system schematic below where it would enter via the bottom of the cylinder. But this can be very energy intensive as the whole hot water contents in the cylinder need to circulate around the system. This loses heat, which in turn makes the heat source turn on to reheat.

Example secondary return pipework configuration

In more recent years the hot water secondary return connection has been within the top section of the cylinder, which reduces the full contents being circulated and reduces the energy usage.

As well as this, Wilo has introduced a programmable bronze pump. You can set the times that the pump is active, to avoid constant circulation, making it even more efficient than a standard pump, resulting in less heat loss.

Secondary return system when connected to Mixergy

What other key aspects can improve the efficiency of this system set-up?

If you’re setting up a hot water secondary return system, you also need to consider the following:

  • The hot water pipework should be insulated to BS5546 to reduce heat loss.
  • The secondary return pump itself should be controlled on a timer and not allowed to work 24/7.
  • A control system like a pipe stat to measure the temperature of the water or by other methods such as P.I.R sensors, can be positioned in spaces such as the bathroom en-suite and above kitchen sinks, which turn the pump on when these areas are occupied, and turn off when they’re not.
  • Towel radiators can also be connected on secondary returns, but these need to be WRAS Approved and made with specific material to prevent contamination of the system water. Although these radiators will emit heat and increase the cylinder’s heat loss which would need to be factored in at the design stage.

How does a Mixergy cylinder work with a secondary return system?

Mixergy cylinders of 210 litres and above in size have a secondary return connection available. Everything you need to consider with a secondary return for a traditional cylinder, also apply with a Mixergy cylinder.

As Mixergy cylinders have a setting that can maintain the target temperature, we don’t need to reheat at a 5ºC temperature drop. This saves energy and is far more efficient than a traditional cylinder.

Mixergy app showing option to maintain the target temperature

Hot water secondary return is a great solution for delivering efficient hot water in larger homes.

Alongside all our other smart control benefits and allowing the home to only heat what they need, Mixergy cylinders are the ideal cylinder solution to coincide.

If you would like to discuss secondary returns or what benefits there are with a Mixergy smart hot water cylinder compared to a conventional hot water cylinder, please contact us.