Frequently Asked Questions

Assisted Ventilation (AV) & Passive Stack Ventilation systems (PSV)

Q. Will the system suck all the heat out of the property?
A. Ventilation is required to control condensation. An air change rate (ach) of between ½ and 1 ach for the whole property has been demonstrated as normally sufficient to control moisture build up. The objective of a good ventilation system is therefore to provide a balance between energy efficiency and indoor air quality.
Passivent systems are no different to fans in that they extract moisture-laden air. They will, however, modulate in response to humidity levels providing ventilation when required thereby maintaining the correct balance.

Q. Why do I not need tricklevents in all the rooms and why only 4,000mm² in dry rooms?
A. The objective of a Passivent system is to create planned air routes from dry rooms to wet rooms with extraction directly from wet rooms to the outside. By looking at the whole house, i.e. background and extract ventilation together, rather than only a single element, it is possible to provide a combined approach. The BBA certificate provides an acceptable alternative to meeting Building Regulations for both background and extract ventilation.
As a result, if a Passivent whole house system is installed, background ventilation is not installed in wet rooms and only 4,000mm² is required in dry rooms.

Q. How long will the humidity sensitive inlets and extracts last?
A. The BBA state that the system “is made of durable materials” and “should have a life equal to that of the building in which they are installed”. The first humidity sensitive products were produced in 1984. Recent tests on some these first products found that there was a less than 5% variation from their original settings.

Q. Will the system (PSV or AV) fill up with grease and dust over time?
A. With both systems (PSV and AV) operating at lower airflow rates it is not a problem that is experienced. The extract cover can be easily removed and washed if required.

Q. Is the system (PSV or AV) suitable for a kitchen?
A. Functioning continuously (as demanded) it will work typically over a longer period than an extractor fan helping to dissipate and get rid of moisture and smells.

Q. If I have an extract (PSV or AV) in the kitchen can I still have a cooker hood?
A. Yes. The cooker hood will provide a high rate of extraction for a short period of time with the Passivent extract providing the benefit of continuous 24/7 extraction with no tenant involvement.

Passive Stack Systems

Q. Without any mechanical parts, how can I be certain that a PSV system will work?
A. We have a wealth of experience having been involved in passive stack ventilation for over 12 years and annually supplying well in excess of 10,000 passive stacks per year.
Passive stack ventilation is based upon proven natural principles whereby hot air rises, the stack effect and wind blowing across the roof providing extra suction (the Venturi effect).
Unlike mechanical extract fans, it is working to meet demand 24/7. So not only will it work, with no mechanical parts, it has nothing to wear out or go wrong. In fact, the BBA assert that “the system should have a life equal to that of the building in which it is installed”.

AV Systems

Q. Am I going to get noise transmission (cross talk) through the ducting on my Assisted Ventilation system?
A. This is not a problem we have experienced in the many years we have been involved with AV systems. Studies which have been carried out have shown the noise transmission to be well below the levels acceptable. Acoustic ducting is available for particularly noisy installations.

Q. On an AV system, how is it possible to link kitchens and WC’s to the same ducting?
A. By having a continuously running fan there is always a suction pressure through the duct to the central extract fan. If the building design were such that two extracts would be placed back to back, we would use a staggered “T” junction in the system design as a failsafe.

Q. I have an internal bathroom or WC, how long will it take an AV system to clear any smells?
A. Even in the closed position (i.e. at low humidity levels), it will still provide 10-15m³ per hour, which on a 2 x 1½m WC should be over 2 air changes per hour.

Q. On a six extract AV system, how do I know each extract is getting the right amount of airflow?
A. The system operates continuously and is self regulating through the humidity sensitive nylon strips in the extract. The extract opens and closes to meet demand ensuring that extract ventilation is provided exactly where and when it is required.

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