Common Mistakes When Replacing Filters for MVHR Units
Regular filter replacement is essential to maintain the efficiency of your MVHR (Mechanical Ventilation with Heat Recovery) unit, reduce energy consumption, and extend the life of your ventilation system. While changing filters is a simple task, manufacturers often provide only basic instructions, leading to common mistakes. Here’s a guide to help you avoid these errors:
1. Not Switching Off the MVHR Unit During Filter Replacement
Always turn off the air handling unit before performing maintenance. Wait a few minutes for the impellers to stop completely. Here’s why this step is critical:
- Safety: There’s a risk of electric shock if any wires or connections are damaged.
- Equipment Protection: Rotating impellers can be damaged or cause minor injuries if accidentally touched.
- Contamination Risk: Larger particles can clog the heat exchanger during filter replacement.
⚠️ Note: If your unit has an electric heater, remember it stays hot even after switching off the unit.
2. Skipping Unit Cleaning During Filter Replacement
Over time, contaminants can bypass filters—especially if using lower-efficiency G4 (Coarse) filters—causing dirt buildup on internal surfaces and filter holders.
- Use a vacuum cleaner to remove larger particles.
- Clean and disinfect surfaces using products safe for metal and electrical components.
3. Neglecting Other Maintenance Tasks
Filter replacement is an excellent opportunity to perform a quick inspection of your MVHR unit. Most manufacturers recommend checking the following:
- The condition and tension of rotary heat exchanger belts (if applicable).
- Rotor drum brushes (if applicable).
- The heat exchanger for dust, debris, or mold contamination.
- Fan impellers—ensure they rotate freely without noise or vibration.
- Drainage and siphons—clean if necessary.
4. Installing Filters in the Wrong Direction
Filters typically have an arrow indicating the correct airflow direction. Installing the filter backward increases resistance by up to 15%, shortening its lifespan.
Tip: in the most cases airflow direction must point from air ducts towards the heat exchanger.
- Exception: For Zehnder ComfoAir Q filters, the arrow indicates "this side up."
5. Mixing Up Supply and Extract Filters
Ensure the supply (outdoor) air filter is in its correct position, especially if it has higher efficiency than the extract filter.
- Misplacing them can cause airflow imbalances, increased energy use, and allow more polluted air into your home.
Tip: Outdoor air ducts are usually insulated, while extract air ducts are not.
6. Incorrect Placement of G4 and F7 Filters on Supply Air
Some MVHR units (e.g., Blauberg, Broder) use two filters on the supply air side:
- G4 filter: Captures larger particles like insects and coarse dust.
- F7 filter: Removes fine particles.
Install the G4 filter closer to the air intake and the F7 filter closer to the heat exchanger.
7. Overlooking Filters in Other Ventilation Components
Filters may also be located in:
- External filter boxes.
- Exhaust air valves and grilles.
- External pre-heaters like the Zehnder ISO-BOX.
Replace these along with the main MVHR filters to maintain system efficiency.
8. Not Resetting the Filter Timer
Most residential AHUs use a timer to monitor filter contamination. If not reset after replacing filters, it will continue to indicate pollution.
- Reset the timer via the control panel or mobile app, following the user manual. Some units have a dedicated button for this.
If you’re unsure about any steps or have questions about replacing your filters, feel free to reach out to us—we’re here to help!