DIY Passive Vents or Fan-Forced Sub-Floor Ventilation?


Before the invention of fan-forced sub-floor ventilation systems, passive ventilation was the normal practice in home building. But do they adequately create cross-flow ventilation in the sub-floor area? This is something to consider before cutting brickwork and embarking on passive vents or fan-forced sub-floor ventilation systems.

To answer this question really depends on the geographical location of the dwelling. Passive ventilation by themselves is a hit and miss affair: If you live on a hill with no surrounding buildings or obstructions there is a good chance that passive ventilation would be adequate. However in a city environment, on a free standing or semi-detached dwelling, it will most likely NOT be effective.

To improve on terracotta passive vents was a wire mesh vent which has a greater air surface area by adapting a 10mm wire matrix centred inside the vent. But the question still remains if there is no external airflow actuating through them what kind of result would be achieved?

Hence the introduction of Envirofan fan-forced sub-floor ventilation systems.

Does that mean an Envirofan has to replace every existing vent around the home? The answer is a resounding ‘no’. The Envirofan fan-forced systems are placed strategically, retro-fitting certain passive vents. For example, where the sub-floor area has the lowest clearance from the ground to the floor an Envirofan single-brick sub-floor ventilation system would replace a vent under that specific area, whereby the extraction process the humidity is drawn out and replaced with fresh air. This then ingresses through other existing passive vents. This is where passive vents have their rightful place in building construction, to act as an air intake due to extraction via the Envirofan fan-forced system. Only then will a passive vent reach its full potential.

So when embarking on a DIY sub-floor ventilation, the choice is yours. Installing passive vents will give a limited result. Coupling passive vents with an Envirofan sub-floor fan-forced ventilation system will give your home the desired objective of effective cross-flow ventilation – making for a healthy and happy home.