DO NOT BUY A VENTIS SYSTEM they do not work as promised and after sales service is the worst I have experienced from any company.
The VENTIS system does absolutely nothing in summer even with the auto whirlybirds it just chews though power with no gain in cooling.
I had high hope for the VENTIS system in winter as I opted for the full blown system with the heat transfer system but due to poor installation using incorrect materials the systems does not work, VENTIS acknowledged the it was installed incorrectly and promised several times to fix the issue but 18 months down the track it is still not fixed and The VENTIS management will not return phone calls.

For the cost of the VENTIS system you are far better off in every aspect installing a air conditioner system with the added benefit of proper heating and cooling once again do not buy the ventis system you have been warned

Approximate cost: $7000