Last updated: March 20, 2026
Spring is often associated with cleanliness and refreshing every corner of the home. However, we tend to overlook the fact that this is the time of year when your MVHR system experiences one of its highest workloads.
As flowers, shrubs and trees begin to bloom, large amounts of pollen are released into the air. At the same time, levels of particulate matter (PM10 and PM2.5) increase due to road dust, construction activity and even Saharan dust travelling long distances across Europe.
It is also important to note that by spring, filters have often already accumulated pollutants from the winter season. During colder months, they trap fine dust, soot, traffic pollution and other micro-particles, meaning they are already heavily contaminated by the time spring arrives.
For this reason, spring is one of the most important times to replace MVHR filters.
What Happens to MVHR Filters in Spring?
In spring, MVHR filters are exposed to additional strain due to intense plant blooming. Pollen from trees, shrubs and flowers enters the air — including plum, cherry and apple trees, ornamental shrubs, and spring flowers such as tulips, daffodils, hyacinths and crocuses.
As a result, the concentration of biological particles in the air increases significantly, and these particles are carried into the MVHR system, where filters act as the first line of defence.
Most pollen particles, such as those from birch trees, are relatively large and can be captured even by coarser filters. However, scientific studies show that under humid or stormy conditions, pollen can break down into much smaller particles (<2.5 µm), which can penetrate deeper into the respiratory system.
For this reason, higher-efficiency filters such as F7 or M5 become especially important, particularly for people with allergies or those seeking cleaner indoor air.
How Does Spring Pollution Affect MVHR System Performance?
Contaminated filters affect the entire performance of the MVHR system. Studies on heat recovery ventilation systems show that when filters become heavily clogged, airflow can decrease by up to 37% — for example, from 142 m³/h to 89 m³/h.
In practice, this leads to:
- Reduced air exchange indoors
- Faster increase in CO₂ levels
- Higher risk of moisture and mould
- Odours lingering for longer periods
Some modern MVHR systems attempt to compensate for filter resistance by increasing fan speed, which can result in higher noise levels and increased energy consumption.
What Do Manufacturers Recommend?
Most manufacturers and industry guidelines recommend checking filters every 3 months and replacing them approximately every 6 months. However, it is emphasised that during spring, replacement intervals may need to be shorter due to increased levels of pollen, insects and dust.
Replacing filters every 3–6 months, depending on your location, helps ensure optimal system performance.
How Does Filter Replacement Affect Your Health?
Studies show that for people with allergies, symptoms can begin at pollen concentrations as low as 50–100 grains/m³. In Lithuania, the “moderate” level of birch pollen alone starts at around 70 grains/m³, meaning that filters can quickly become saturated with allergens in spring.
If the pollen season begins with old, contaminated filters, some of these particles may enter indoor spaces, increasing the likelihood of allergy symptoms.
Spring is a period when your MVHR system operates at its most intensive level — filters must capture pollen, dust, smoke and other pollutants. If MVHR filters become clogged, airflow decreases, indoor air quality deteriorates, and the risk of allergies increases.
You can easily find and purchase the right MVHR filters based on your unit model, size and filtration class at Filterloop.eu — helping ensure that your indoor air remains clean and fresh throughout the spring season.
Article prepared by Paulina Padeginskaite
