What should you know about the supply air temperature? What does the exhaust air temperature indicate?

Why is 17°C the ideal temperature setting?

The manufacturer recommends setting the temperature to 17°C. The ventilation unit aims to produce 17-degree air by transferring heat energy from extract air to supply air with a heat recovery cell. During freezing temperatures, the system also uses a post-heating radiator together with the heat recovery cell. The post-heating radiator is activated when the heat recovery cell no longer suffices for heating the supply air to the target temperature.

The higher the temperature setting, i.e. the target supply air temperature, the more the post-heating radiator needs to work to heat the supply air. It is recommended that the temperature setting be kept at least 2–3 degrees below room temperature, as cooler supply air enhances ventilation. The temperature can even be set as low as 15°C, provided that there is no uncomfortable cold draught of air. Ultimately, the room air should be heated to the desired temperature by a different means than the ventilation unit.

Hot or cold supply air – where is the problem?

Even if the ventilation unit’s target temperature is set to 17°C and the unit works to keep the supply air at this temperature, sometimes the unit fails to do so. The unit’s heat recovery cell can heat the supply air to up to 21°C.

For example, the temperature of supply air can peak temporarily during the heating period due to sauna bathing, as the heat recovery system heats the supply air with the heat of extract air. In sub-zero temperatures, the heat from the sauna also heats outdoor air, maintaining a lower supply air temperature and letting the post-heating radiator rest for a short while.

The supply air temperature can also momentarily rise sharply in warm weather, especially in smaller homes. The ventilation unit is not an air conditioner, and it is not designed to cool warm outdoor air. A separate cooling device, such as an air-to-air heat pump, is required for that purpose. In summer, it is recommended that the heat recovery cell be used to recover cool night air to reduce the room air temperature in the night. 

In severe frost, the supply air temperature falls during the defrosting cycle. This applies in particular to compact units without a post-heating radiator for defrosting. During the defrosting cycle, the heat recovery cell is in Bypass mode. Heat from extract air is not transferred to supply air but keeps the cell defrosted.   

Vallox Aito Kotilämpö is an exception

The MyVallox Control panel in Vallox Aito Kotilämpö is similar to that in Vallox ventilation units. The supply air temperature reading indicates the temperature of the heat recovery cell. The control panel does not show the temperature of air entering the circulating air duct during the heating period. Instead, an external sensor measures the room air temperature and triggers the heating radiator to circulate air at the target temperature. 

Exhaust air temperature shows the system status

High exhaust air temperature indicates that the fresh air grille or filters are blocked or the unit’s bypass damper is in Bypass mode instead of Heat Recovery mode. During the defrosting cycle, the bypass damper switches to Bypass mode and the exhaust air temperature rises closer to the indoor temperature.

When the heat recovery cell is in Heat Recovery mode, the exhaust air temperature falls radically – even down to -10°C in severe frost. If the indoor air temperature is too high, for example due to sauna bathing, the exhaust air temperature can also rise momentarily, as the heat recovery system does not need all the heat energy to heat the supply air.

If the exhaust air temperature rises, it is best first to check the cell status in the home view of MyVallox Cloud. The cell will be in either Bypass, Heat Recovery or Defrosting mode. If the cell is in Heat Recovery mode, the bypass damper should be closed and the exhaust air temperature low. In summer, when the cell is in Bypass mode, the exhaust air temperature should be the same as the air temperature in the room from which air is being extracted.

Keep the ventilation unit on and let the experts adjust the settings

A ventilation unit has many settings that should be left to professionals. For example, in winter, the fan speed should be kept high enough and the internal carbon dioxide and humidity sensors must be on to keep the cell defrosted. This means that you must keep the unit in the At Home mode whenever you are home and avoid setting it to the Away mode in an attempt to save energy. Let the ventilation unit do its job. Optimal operation requires that the settings be correct. If you suspect that something is wrong with your unit, do not hesitate to contact the service provider that installed the unit, or the property manager, to have a professional check the settings. You can find experts near you through our map service.