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For well over half a century, mechanical ventilation has been a staple in UK homes, primarily in bathrooms, kitchens, and utility rooms. Intermittent extractor fans have long been the go-to solution for removing moisture and stale air, proving their continued relevance. However, a new contender has emerged—the dMEV (Decentralised Mechanical Extract Ventilation) continuous running fan, offering superior protection against humidity, pollutants, and stale air while operating quietly and efficiently.
The Rise of Continuous Ventilation
Though not entirely new, dMEV units have become more affordable in recent years. These fans continuously extract air at a low speed and increase airflow when necessary, effectively controlling dampness and mould. When paired with proper heating and insulation, dMEV fans provide an excellent solution for maintaining good indoor air quality.
However, modern homes are designed to be highly insulated for energy efficiency, reducing natural airflow. While this conserves heat, it also traps pollutants and moisture inside and restricts fresh air from returning into the building. New builds and extensive renovations benefit from Mechanical Ventilation with Heat Recovery (MVHR) systems, which regulate both extraction and fresh air supply while retaining heat. However, retrofitting MVHR in existing homes not undergoing major renovations is often costly and disruptive.
The Airflow Dilemma in Well-Insulated Homes
Many modern homes prioritize heat efficiency but lack effective ventilation. Extractor fans struggle in sealed homes without a proper fresh air supply to replace the extracted internal air and balance the internal air pressure. In older homes, natural airflow through less insulated construction helps maintain balance. But how can modern homes achieve this balance?
One solution is regulated air vents in windows. For example, keeping bathroom vents closed prevents cold air from rushing in while showering, which speeds up the condensation process. Instead, opening vents in other areas, such as the living room or hallway, ensures fresh air enters the home to balance the air pressure while making sure the returning air into the bathroom is coming from within the house and therefore already up to temperature.
Passive Input Ventilation (PIV): An Alternative Approach
For homeowners hesitant to let cold air seep in through vents, Passive Input Ventilation (PIV) offers an alternative. Instead of extracting, PIV actively introduces fresh, filtered air into a home, typically via a loft-mounted unit. By maintaining positive air pressure, PIV forces stale, humid air out. In modern homes, regulated window vents help facilitate this process, while built-in heating elements in some PIV systems slightly warm incoming air to prevent chills.
However, due to high moisture levels and airborne particulates from cooking, building regulations still require effective extraction in bathrooms, kitchens, and utility rooms. This raises an important question: Can PIV and dMEV systems work together?
Combining dMEV and PIV: A Strategic Approach
While dMEV and PIV can be installed in the same home, careful planning is needed. If a dMEV fan is placed in a bathroom on the same floor as a PIV system, it may disrupt the PIV’s effectiveness by monopolizing the flow of fresh air to the bathroom, undermining the flow to other rooms within the home. In such cases, intermittent fans are a better option, allowing the PIV to distribute air more evenly for the majority of the time.
However, a single dMEV fan can work well in a ground-floor utility room, WC, or kitchen in an extremity of the building, where they can help promote constant airflow from the PIV upstairs to the further downstairs areas. This setup can mimic the balanced ventilation of an MVHR system without the high retrofitting costs.
Finding the Right Balance
As home ventilation technology advances, finding the right balance for your specific needs is essential. While dMEV fans offer constant extraction benefits, traditional intermittent fans still play a valuable role. Likewise, PIV systems introduce fresh air but must be integrated strategically to avoid airflow imbalances.
Ultimately, achieving optimal indoor air quality requires a tailored approach - one that considers insulation levels, home layout, and ventilation challenges. Whether through dMEV, PIV, intermittent fans, or a combination of systems, modern homeowners have more tools than ever to create a healthier, more comfortable living environment.