Knowing which way to install MVHR filters, and the direction they should face, is important for system efficiency and clean indoor air. Many users fit filters the wrong way around. This reduces performance and shortens the life of the filter. In this guide, we explain the correct direction for common MVHR filter grades. These include G3, G4 (blue and white), and M5 filters. Get the most from your filters by installing them correctly.
G2 Filters – Basic Pre-Filtration with Flexible Direction
G2 filters are low-grade coarse filters used for very basic filtration. They are typically made from a uniform synthetic or fibrous material. Like G3, G2 filters are multi-directional and can face either way when installed. G2 filters catch larger particles such as dust. They are commonly used in environments with light dust levels and offer minimal airflow resistance.
G3 Filters – Multi-Directional Simplicity
G3 filters are made from a uniform, synthetic material, there is no front or back to worry about. This makes G3 filters multi-directional. You can install them either way, and they will work the same. G3 filters are low-grade pre-filters and are used to catch larger dust particles. G3 is a non-woven white polyester, which will give you the lowest level of protection, and usually come as standard from the original manufacturer.
G4 Filters – Blue Side Faces the Dirty Air
G4 filters often have two layers: blue and white. The blue side is coarser and should face the incoming, dirty air. The white side is finer and should face the clean air, going into the MVHR unit. This design helps trap larger particles first and protects the finer media which helps the filter last longer. Placing the filter the wrong way reduces performance. Always place the blue side facing the air intake.
M5 Filters – Fluffy Side Faces the Dirty Air
M5 filters have a progressive structure, where one side is smooth, and the other side is fluffy. The fluffy side should face the dirty air, as this side captures larger particles. The finer, smoother side finishes the filtration by capturing tiny particles and allergens. M5 is a mid-grade filter and offers better filtration than G4. Correct placement improves dust capture and airflow.
Why Filter Direction Matters in MVHR Systems
Placing filters the wrong way increases resistance which makes the MVHR fan work harder. It uses more energy and may lower airflow. Incorrect installation also causes the filters to clog faster and reduces indoor air quality. Directional filters are engineered to work in a certain order and the layers must filter air in stages.
When to Change MVHR Filters
You should change most filters every 3 to 12 months, however in dusty or urban areas, change them more often. Check filters regularly for dust build-up, as a blocked filter reduces airflow and makes your MVHR system inefficient. Clean filters mean cleaner air and better energy performance.
Conclusion
G3 filters can face either way, whereas G4 filters must have the blue side facing the dirty air and M5 filters must have the fluffy side facing the dirty air. Correct filter placement is vital for airflow, air quality, and energy use. Always follow the material layout or direction arrows. For expert advice and quality filters, shop at MVHR.shop.
