Affordable mechanical ventilation has been a staple in homes across the UK for nearly a century. Typically installed in bathrooms, kitchens, and utility rooms, these intermittent fans remain widely available today, offered by numerous manufacturers in various designs, sizes, and functionalities. Their continued presence in the market underscores the ongoing relevance of intermittent ventilation in modern households.
However, a new player has emerged in the field of home ventilation—the dMEV continuous running fan. This innovation offers superior protection for indoor air quality by effectively reducing humidity, stale air, and pollutants, all while operating quietly and efficiently.
Although dMEV systems are not a brand-new concept, their affordability has improved significantly in recent years, making them a more accessible option. By maintaining continuous ventilation at a controlled low speed, with the ability to boost airflow when needed, these units help prevent the buildup of humidity and airborne contaminants. This makes them particularly effective in spaces prone to damp and mould, positioning them as one of the best solutions for combating black mould when combined with proper heating and insulation strategies.
Yet, ventilation requires a balanced airflow, which can be challenging in newly constructed or highly insulated homes. The challenge lies in the desire to retain heat for energy efficiency while also ensuring proper air circulation. While insulation helps maintain indoor temperatures, it also traps pollutants and moisture while preventing fresh air from entering. In new builds and major renovation projects, installing a Mechanical Ventilation with Heat Recovery (MVHR) system, which controls both extraction and fresh air supply while retaining heat, is an excellent solution. However, retrofitting MVHR into existing homes can be costly and disruptive.
Additionally, many homes built over the last two decades were designed with energy efficiency in mind, but without fully considering the impact on airflow. As a result, these homes often lack effective strategies to mitigate ventilation challenges.
So, what exactly is the problem? In simple terms, attempting to extract air from a sealed space without allowing replacement air to enter creates negative pressure, causing traditional extractor fans to struggle. Over time, the increasing resistance can cause them to slow down or even stop working. Intermittent fans rely on the ability to create a slight negative pressure, drawing fresh air into a room from the surrounding home. In older buildings, air naturally flows back into the home through the porous nature of the fabric of the structure. However, in modern, well-insulated homes, this airflow is significantly restricted.
For these tightly sealed homes, regulated air vents in windows can provide a controlled solution. For example, while it's not ideal to introduce cold air into a bathroom during a shower, since this accelerates condensation, it is necessary to allow fresh air into the home to maintain balance. By keeping bathroom vents closed but opening vents in living areas or hallways, fresh air can enter the home, warm up as it moves through, and ultimately reach the bathroom, ensuring the extractor fan operates efficiently.
Understandably, homeowners who have invested in insulation may be reluctant to introduce cold air into their homes. For those seeking an alternative solution, Positive Input Ventilation (PIV) offers an effective approach. Rather than extracting air, PIV units actively push fresh, filtered air into a home, typically from a loft-mounted system. This creates a gentle, continuous positive air pressure that drives stale and humid air out. In older buildings, the existing gaps and porous materials facilitate this air exchange, while in modern homes, passive air vents in window frames allow for controlled ventilation in an outward rather than inward direction. Some PIV units even include heating elements to warm incoming air, helping to prevent cold drafts.
Despite the benefits of PIV systems, current building regulations still mandate effective extract ventilation in bathrooms, kitchens, and utility rooms to manage moisture and airborne pollutants. This raises an important question: Can dMEV fans be installed alongside a PIV unit?
The short answer is yes, but careful consideration is needed. The placement of a dMEV fan can impact the effectiveness of a PIV system. For example, if a PIV unit is installed to improve air quality in first-floor bedrooms suffering from condensation, placing a dMEV fan in the first-floor bathroom could create a local negative pressure. This would draw the PIV-supplied air predominantly into the bathroom, reducing its effectiveness in the bedrooms. In this case, a traditional intermittent extractor fan would be a better choice, as it only operates when needed, allowing the PIV system to service the entire floor more effectively. Furthermore, a PIV unit can help mitigate backdraft issues in a dormant bathroom intermittent extractor fan, providing a continuous ventilation effect similar to a dMEV unit without disrupting overall airflow balance.
On the other hand, dMEV fans can be effectively integrated with PIV systems in specific situations. For instance, if a PIV unit is installed in a loft and supplies fresh air through a landing ceiling vent, a dMEV fan positioned in a ground-floor utility room, WC, or kitchen located in the extremities of the home can help promote the downward movement of the introduced air. This setup mimics the air circulation of an MVHR system, maintaining balanced ventilation without the need for extensive ductwork or the discomfort of cold air ingress during winter.
Ultimately, while advancements in ventilation technology continue to emerge, the fundamental principles of air movement remain unchanged. Whether utilizing intermittent extractors, continuous dMEV fans, or PIV units, achieving the ideal balance between energy efficiency and indoor air quality requires a strategic approach tailored to each home's specific needs.