Optimising ZEB Water Flow Temperature

Use this article to:

• Understand what the water flow temperature setpoint does
• Compare the effects of higher vs lower flow temperature setpoints
• Learn how flow temperature impacts efficiency and noise
• Check important safety considerations for hot water

1. What is the water flow temperature setpoint?

The water flow temperature setpoint determines the temperature of the water circulating through your radiators.

By default, the ZEB is preset to 70°C when it’s delivered. You can adjust this setting between 35°C and 80°C in the tepeo app, under ZEB Settings.

The ZEB is designed to be highly tolerant of different heating system setups and controls. Unlike heat pumps or (to a lesser extent) condensing boilers, the ZEB largely maintains consistent performance regardless of your heating system’s complexity. However, optimising the flow temperature can improve your overall comfort and experience.

2. Effects of different flow temperature setpoints

Higher flow temperature (e.g. 80°C)

• Radiators heat up quickly, so rooms warm up faster.
• More residual heat is emitted after the thermostat stops calling for heat, which can cause noticeable air temperature swings and feel less comfortable.

Lower flow temperature (e.g. 55°C)

• Rooms warm up more gradually.
• Indoor temperatures are more stable, with fewer swings, which can feel more comfortable.
• You may need to run your heating for longer to reach the same target air temperature.

3. Efficiency and running costs

For many systems (e.g. heat pumps or condensing boilers), running at lower flow temperatures improves efficiency. This is not the case for the ZEB.

One key advantage of the ZEB is that its efficiency is largely unaffected by the flow temperature setpoint:

• Running the internal air fan at maximum speed uses only slightly more power than at minimum speed.
• The efficiency and cost of operating the ZEB remain essentially the same, regardless of how hard it’s working.

Whether you choose a higher or lower flow temperature setpoint, the energy required to raise your indoor air temperature from, for example, 18°C to 21°C is the same. The main difference is how quickly heat is transferred and distributed.

At the lowest flow temperature setpoint (35°C), your radiators may feel cool to the touch, but they can still heat the room gradually as long as they are warmer than the surrounding air.

4. Noise and comfort

The noise level of the ZEB depends mainly on:

• Where it is installed (e.g. close to living spaces)
• When the thermostat is calling for heat

When the ZEB starts up and works harder to reach the flow temperature setpoint, you may hear the internal air fan. Once the flow temperature is reached and the fan slows down, the ZEB is essentially silent. This startup noise is similar to a traditional gas boiler, but without the characteristic “whoosh”.

Lower flow temperatures can also help reduce system noise:

• Traditional gas boilers often cause pipes to creak and groan as they heat up and cool down.
• The ZEB’s smoother operation, especially at lower flow temperatures, significantly reduces these noises.

5. Important safety and usage considerations

• Hot water safety:
  If your ZEB is connected to a hot water cylinder used for baths or showers, do not set the flow temperature below 60°C. This helps to reduce the risk of Legionella bacteria growth.

• Heating schedules:
  If you reduce the flow temperature setpoint, consider extending your thermostat’s heating schedule to allow more time for your home to warm up.

By carefully adjusting your ZEB’s flow temperature setpoint, you can balance comfort, noise and safety while maintaining efficient operation.