Mechanical Ventilation with Heat Recovery (MVHR) systems are designed to provide fresh, filtered air while recovering heat from outgoing air, ensuring a comfortable and energy-efficient home. However, certain mistakes can significantly impact their efficiency and effectiveness. Here are some of the most common issues homeowners face and how to avoid them.
1. Incorrect Installation and Poor System Design
One of the most significant factors affecting an MVHR system’s efficiency is how it is installed. Poorly designed ductwork, incorrect positioning of the unit, or insufficient airflow balancing can severely impact performance.
- Poor duct layout: If the ducting has too many bends or is unnecessarily long, airflow resistance increases, making the system work harder.
- Incorrect unit placement: The MVHR unit should be installed in a location that minimises noise and vibration while allowing easy access for maintenance.
- Lack of proper airflow balancing: If the system isn’t correctly balanced, some rooms may receive too much or too little ventilation, reducing overall efficiency.
2. Neglecting Filter Changes
MVHR filters play a crucial role in maintaining air quality and ensuring optimal performance. Over time, these filters accumulate dust, pollen, and other airborne particles, restricting airflow and reducing efficiency. A clogged filter forces the system to work harder, consuming more energy and potentially leading to mechanical failures. When filters become too dirty, they can also lead to poor indoor air quality, exacerbating allergies and respiratory issues.
It is essential to check and clean filters every 3-6 months and replace them as per the manufacturer’s recommendations to keep the system functioning at its best.
3. Turning the System Off
Some homeowners mistakenly turn off their MVHR system to save energy, particularly when they leave the house or during mild weather. However, doing so can cause problems such as:
- Increased condensation and mould growth: Without continuous ventilation, excess moisture can build up, leading to damp problems.
- Poor air circulation: Turning off the system reduces the supply of fresh air and removal of stale air, leading to stuffy indoor conditions.
- Higher heating costs: If the system is off, warm air from inside the house escapes without being recovered, increasing heating bills.
Instead, it’s best to keep the system running continuously at a lower setting to maintain a healthy indoor environment and prevent moisture-related problems.
4. Blocking or Closing Vents
MVHR systems rely on a network of supply and extract vents to distribute fresh air and remove stale air efficiently. Placing furniture in front of vents, covering them, or allowing dust and debris to build up can obstruct airflow, causing the system to struggle. This can lead to poor ventilation, uneven air distribution, and even an increase in indoor pollutants.
Ensuring that vents remain clear and unobstructed helps the system function as intended, maintaining good air circulation throughout the home.
5. Using the Wrong Filters
Not all filters offer the same level of performance. MVHR filters come in different classes, including Coarse (G3, G4), Medium (M5, M6), and Fine (F7). Using the wrong filter type can:
- Reduce the effectiveness of filtering pollutants
- Restrict airflow if the filter is too dense for the system
- Lead to higher energy consumption due to increased resistance
Standard filters may not be sufficient in urban areas with high levels of fine dust and pollutants. It’s important to select the right type of filter, such as an F7-grade filter, to effectively capture fine particles, pollen, and pollutants. High-quality filters not only improve air quality but also enhance the longevity and efficiency of the MVHR system.
6. Lack of Regular Maintenance
Regular servicing by a professional is essential to keep an MVHR system in peak condition. During a service, a technician will check for blockages, inspect the heat exchanger, and ensure all components are functioning correctly. They will also look for signs of wear and tear that could lead to breakdowns if not addressed. Neglecting maintenance can result in reduced performance, higher energy consumption, and even system failures over time.
Scheduling an annual service ensures that the system remains efficient and continues to provide optimal air quality.
7. Improper Insulation of Ductwork
In colder months, uninsulated or poorly insulated ducts can lead to condensation forming inside the pipes. This moisture can then drip down into ceilings or walls, causing damage and potentially leading to mould growth.
- Insulated ducts prevent condensation and ensure that recovered heat isn’t lost before it reaches your rooms.
- Proper insulation also helps maintain energy efficiency by reducing heat loss.
8. Not Adjusting Settings for Seasonal Changes
Your MVHR system should be adjusted according to seasonal changes to maintain optimal efficiency.
- In winter: Ensure the heat recovery function is fully operational to retain as much warmth as possible.
- In summer: Some systems have a summer bypass mode, which allows cooler outdoor air to circulate without heat recovery, helping to reduce indoor temperatures.
- Humidity settings: Adjusting humidity controls can help prevent excessive dryness in winter and condensation in summer.
9. Ignoring Noise Issues
If your MVHR system is noisier than usual, it could indicate an underlying issue, such as:
- Clogged filters restricting airflow
- Loose or vibrating ductwork
- Imbalanced fans working harder than necessary
Addressing noise problems early can prevent more significant issues down the line.
10. Using the Wrong Fan Speeds
Most MVHR systems have different fan speed settings for various conditions. Running the system at an unnecessarily high speed can waste energy, while a too-low setting may not provide adequate ventilation.
- Use a lower setting when the home is unoccupied.
- Increase fan speed during cooking, showering, or when more people are in the house to remove excess moisture and pollutants efficiently.
Final Thoughts
An MVHR system is an excellent investment for maintaining a comfortable and energy-efficient home. However, avoiding common mistakes like neglecting maintenance, obstructing vents, and using incorrect settings is crucial to ensuring its longevity and effectiveness. A well-maintained system will provide fresh, clean air while minimising energy waste. By staying proactive and regularly checking the system’s components, homeowners can enjoy fresh, filtered air while keeping energy consumption in check, creating a healthier and more comfortable indoor environment.
If you’re unsure whether your MVHR system is functioning optimally, consider scheduling a professional inspection to ensure it’s operating as efficiently as possible.