About Bypass

About Bypass

Published 30. 05. 2023

Just like many competitors, our Futura heat recovery unit also includes a function called “bypass”. When activated, it can operate automatically in summer mode.
Let’s see how this function really works.

It is not desirable for a heat recovery unit to transfer heat in summer. When bypass is active, the bypass duct leads the fresh air around the heat exchanger and prevents this cooler outside air from being heated by the warm exhaust air. Bypass is therefore used when it is hot inside and cold outside and we do not want the air inside the houseto be additionally heated by the heat exchanger.

“The bypass is running, but we are hot inside. Shouldn’t the bypass function prevent the supply air from getting warmer?”

Yes, the bypass function prevents the supply air from being heated. But: you cannot expect it to cool the air in your home like air conditioning. The function itself does not serve to cool the air in your home. It only ensures that the incoming fresh air is not heated by the warm exhaust air. The bypass only prevents further heat build-up inside the house.

What is the effect of the bypass function

  • fresh supply air is not heated up because it passes around the heat exchanger
  • heat does not build up inside the house = opposite of winter operation
  • the bypass duct in the Futura unit serves only as a secondary function, thus it is not optimized for high air flow (as in any other heat recovery unit)
  • if we have the bypass active, the unit operates at higher speed, which means—higher noise and higher wear of the fans.

We do not recommend to use bypass for a long time.
We recommend activating the bypass only in case of emergency. For example, if you are away from home and do not want to leave the windows open.

In transitional periods (winter/spring and summer/fall) you can achieve much better effect by opening your windows. The optimal combination is the Futura with the CoolBreeze module, which is designed to provide efficient and continuous cooling.

How the bypass works in Futura

To protect the unit, the bypass function is disabled in winter mode. Therefore, you can only enable bypass in non-winter period.
The heat recovery unit switches between winter/summer mode completely automatically. The transition is determined according to the law, which sets the conditions for the beginning and end of the heating season (from 1 September to 31 May of the following year). The length of the heating season can of course vary from year to year.

One of the main criteria for enabling the automatic bypass function is that outside temperature must be => 8°C. Measurements are taken every morning, afternoon and evening. If the average of the readings is => 8°C, the bypass can be activated.

For the bypass to be triggered, the following conditions must be met:

  • you have activated the bypass function in the mobile app
  • the unit is running in summer mode
  • the outside temperature is => 8°C
  • the fans are in motion
  • the temperature scenario as shown in the figure below is met.


Set temperature = 22°C
Outdoor temperature = 18°C
Indoor temperature = 24°C

In this case we want to lower the indoor temperature (from 24°C to 22°C). If the air goes through the heat exchanger, Futura brings in air somewhere in between, i.e. we will never be able to reduce the temperature to exactly the desired 22°C. The bypass does let the outside temperature of 18°C inside the house. but it is much more efficient and easier to let that 18°C into the house directly through the windows, not through the Futura or its bypass duct.

When the above conditions are met, the bypass automatically switches on.

In cases where the morning temperatures are around 9°C, the afternoon temperatures jump up to 20°C and according to the law we are still in winter mode (i.e. heating season has not yet ended), we have no other (or better) option but to get a good window ventilation in the morning when the air is still cold.