Introduction
If you or anyone in your household suffers from hay fever, asthma, or other respiratory allergies, the quality of the air inside your home matters enormously. We spend up to 90% of our time indoors, and the concentrations of allergens, pollutants and irritants inside poorly ventilated homes can be significantly higher than outdoors.
MVHR (Mechanical Ventilation with Heat Recovery) is increasingly recognised as one of the most effective ways to maintain excellent indoor air quality, not just by replacing stale air, but by actively filtering incoming air before it enters the living space.
What allergens does MVHR filter?
Every MVHR unit has a filter on the incoming fresh air supply. The grade of the filter determines what it can capture. The most common filter grades in residential MVHR are G4 and F7.
G4 filters (coarse filter grade)
G4 filters capture larger particles - dust, insects, larger pollen grains, and airborne debris. They are typically used as the first stage of filtration, protecting the MVHR unit's heat exchanger from clogging. G4 filters alone are not sufficient for allergy sufferers.
F7 filters (fine filter grade, now classified ePM1 55% under ISO 16890)
F7 filters capture fine particulate matter, including most pollen species, fine dust particles, mould spores, some bacteria, and particles as small as 1 micron. For hay fever and asthma sufferers, an F7 (or better) filter on the incoming air supply makes a genuine, measurable difference to indoor allergen levels.
Many premium MVHR units allow the filter grade to be upgraded. If you are specifying a new MVHR system and allergy management is a priority, specify an F7 filter on the supply side of the MVHR unit as a minimum.
Important: filter grade also affects pressure drop. Higher-grade filters (F7 and above) create more resistance to airflow than G4 filters. This means the MVHR unit has to work slightly harder, which can marginally increase energy use and noise. However, the health benefits for allergy sufferers typically outweigh this trade-off significantly.
Pollen: the numbers tell the story
The UK pollen season now extends from late February (tree pollens) through to October (mould spores), with grass pollen (the most common trigger for hay fever) peaking between May and August. During high pollen days, outdoor pollen counts can reach several thousand grains per cubic metre of air.
In a home with open windows, indoor pollen concentrations can rapidly approach outdoor levels. In a well-sealed, MVHR-equipped home with an F7 supply filter, indoor pollen counts remain very low throughout the season, as the only air entering the house passes through the filter.
Mould spores and humidity control
Mould is also a major asthma trigger, and mould growth is fundamentally a moisture problem. MVHR systems continuously extract humid air from kitchens and bathrooms, the primary sources of moisture generation in a home, and replace it with drier fresh air. This keeps relative humidity at healthy levels and prevents the condensation that allows mould to establish itself.
The combination of humidity control and incoming air filtration makes MVHR uniquely effective at managing both the conditions that allow mould to grow (humidity) and the allergen that results from it (mould spores).
MVHR vs opening windows
Opening windows is the traditional approach to home ventilation, but it has obvious limitations for allergy sufferers; you are letting the allergen in along with the fresh air, together with insects and security issues.
MVHR allows you to have continuous, healthy levels of ventilation 365 days a year without bringing in pollen, traffic pollution or other outdoor allergens. In a well-designed MVHR home, windows can remain closed on high-pollen days without any compromise to indoor air quality.
Other indoor air quality benefits
Beyond allergens, MVHR also removes and dilutes:
- Volatile Organic Compounds (VOCs) from furniture, flooring, cleaning products and cooking
- Carbon dioxide (CO2) from breathing — high CO2 causes tiredness, poor concentration and headaches
- Cooking odours and steam
- Formaldehyde and other off-gassing compounds from building materials
For asthma sufferers, VOCs and particulate matter are significant triggers. A home with MVHR and good F7 filtration typically has dramatically lower concentrations of these compounds than a naturally ventilated or intermittent fan-ventilated home.
Keeping your MVHR filters effective
An MVHR system only filters incoming air effectively if its filters are in good condition (Learn more here in one of our other blogs). A clogged filter makes the motors work harder increasing noise, passes more pollutants and can harbour bacteria and mould of its own. For allergy sufferers, filter maintenance is particularly important:
- Lightly vacuum filters regularly to remove excess debris and extend filter life
- Check filters every three to six months
- Replace filters every six to twelve months as a minimum, more frequently in urban areas or during high-pollen seasons
- Always use genuine manufacturer-approved filter cartridges (not generic alternatives )
- Consider upgrading to an F7 filter if your unit currently runs a G4 supply filter
Epicair supplies genuine replacement filters for all major MVHR brands, including Ubbink, Zehnder, Vent Axia, Airflow and Nuaire. Visit our MVHR Filters page or call 01892 600121 to find the right filters for your unit.
If you are planning a new home or renovation and allergy management is a priority, MVHR with good supply filtration is one of the most effective long-term investments you can make in indoor air quality. Why not talk to our UK experts on 01892 600121 or email mvhr@epicair.co.uk, and we will be delighted to help you!
