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Airflow through the Unovent fan

9 June 2016
Airflow through the Unovent fan Airflow through the Unovent fan Blog

A number of Unovent ducted solution competitors are advising their potential customers that the Unovent system has inadequate airflow, both for the homes and in comparison to their own competing system. They are misleading those who genuinely wish to have a healthy home at an affordable price with low running costs.

The issue is actually about a range of differences between the unique Unovent and ducted systems which make such comparisons of air flow, fan size, blade diameter a waste of time. In spite of that, a number of ducted competitors have evolved a sales technique based on diversion rather than relevant facts.

Here are some important points:

Each Unovent fan (1.08 watts) pushes up to 60 cubic metres of air per hour from the roof cavity into each living space (depending on the condition and type of filter). If it’s a 5 fan system that’s up to 300cmph.  The only resistance the Unovent fan has to overcome is the filter.  If there was no filter, the air flow would be up to 90 cubic metres per hour for each Unovent fan.

A Unovent outlet is typically placed in the corner diagonally opposite the door.  This enables the air coming through the outlet to put the air in the room under slight pressure, sufficient for all air in that room to be continuously replaced. The old air goes out the door, down the hall and exits the house under the outside doors, through kitchen fans, etc.  (Physics states that air moves from a place of higher pressure to a place of lower pressure - that is why the old air leaves the room).  Testing discovered one change of air per hour was an ideal rate of change and good results were achieved at as low as one half a room change per hour. The average bedroom sizes are : Single 25 cubic metres / Double 35 cubic metres. Therefore a single Unovent fan is changing the air far more often than is required – quietly and without draughts.

A typical ducted system, needs a large expensive fan ranging from 80 to 150 watts. Some are larger and sometimes, two fans are required. Most of this pressure producing resource is required to move the air through the highly restrictive flexible ducting (this has been tested and proven and well understood in the air management industry).  Ducted system room outlets cannot be easily placed in the corner diagonally opposite the door because they would need an extra length of expensive ducting in each room and someone crawling into the tapering eaves to install it.  This would increase the flow friction/resistance and require an even larger noisier fan.

Testing, by putting smoke through them, has shown air flows from ducted outlets placed in test rooms near the door typically require 3 to 6 times the Unovent airflow to make the air in the room disturbed enough to eventually flow out of the room.  When outlets are placed just inside the door, there is a tendency for the air in the room to stay put (static) or otherwise go straight out the door because the air between the outlet and the outer walls is under pressure going nowhere.  This is not as effective as the Unovent lower volume/flow, diagonally opposite the door solution.  Smoke through a Unovent outlet placed as recommended simply drifts across the room and out the door. At a lower flow rate of air per hour with Unovent, there is no requirement to slow down the air flow as the roof air gets colder.  When the temperature of the air in the roof space is too low for this air to be brought into the rooms, the Unobrain supplied with all Unovent systems switches the Unovent outlets off.

As a result, all ducted home ventilation systems, (ie. every other system in the world) are far less efficient than a Unovent system. It's simple proven physics.