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How to replace the AHU filters correctly?

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This is one of the main questions that arise when a customer receives 2 ventilation filters. Especially when you change them the first time. Actually changing filters is easy, so you don’t need to pay any installers to do it. Just follow these rules

1. If the filter classes are different, a more efficient filter is always installed on the outdoor air duct.

Meanwhile, G3-G4 (Coarse) or M5 (ePM10) class filters are used for exhaust air filtration, as they provide sufficient protection of the recuperator from contamination while using less energy. By installing an F7 (ePM2.5 or ePM1) class filter to extract exhaust air, you will not only pay more for the filter, but also significantly increase the pressure loss in the duct.

Where to install a more efficient filter you may find:

  • In the diagrams given in the instructions. On our website, we provide instructions for many manufacturers: Komfovent, Salda, Flexit.
  • According to airflow markings near the duct connection on the ventilation unit.

In some cases, if you do not find the manual or the airflow is unmarked, the following “life hacks” may help:

  • The duct from the outdoor is usually insulated and extract air duct not.
  • Outdoor air, following the airflow, after the heat exchanger is usually heated by a heater.

Pic. 1. SALDA Smarty 2R V Plus scheme with marked filters 

Pic. 2. Schemes of Komfovent Domekt units. Supply (outdoor) air filter is marked as 5.

2. The direction of air on the air filter sticker should correspond to the airflow direction in the air handling unit.

If the filter is placed incorrectly it will result in significant pressure losses. Therefore, most manufacturers have labeled airflow directions near the filter mounting places. However, if any manufacturer “forgets” to do so, check the instructions. The filter arrow must match the direction of the air flow in the flow charts.

Alternative tip: The filter primarily protects the heat exchanger from contamination, so the filter arrow should always point towards the heat exchanger in the direction of air flow.

uni 2 srautine schema

Pic.3 Flow diagram of FLEXIT UNI 2

3. The last task is to reset the filter timer (if no pressure sensors are installed for filter pollution monitoring). More advanced manufacturers even have timer reload buttons on the AHU. However, in most cases, you will get to do it on the remote control panel or on the mobile app. Refer to the remote control manuals on the manufacturer’s website for information on how to do this.

Tip: You can also adjust the timer period after evaluating filter contamination.

Also, some manufacturers, e.g. FLEXIT or SALDA have detailed videos on how to change filters on their websites. Have a good time watching ????