This is about how I asked for a modification to the standard Ventis system, how it performed, my conclusions, and recommendatations. If you just want the summary version about Ventis then read the last section.

How Ventis works

Ventis works by pumping cool air into your warm house. It isn’t an air-conditioning system and can’t actively cool hot air. It simply moves air about. The “secret” to Ventis is that it only uses a low power fan (about 100W, but don’t quote me) instead of an airconditioner that will use up to 100 times that power.

At the end of the day a house will still be too hot because of the heat that has been stored in the bricks etc during the day. Meanwhile the air outside is much more comfortable. The Ventis system will kick in and pull in that cool air.

My thoughts

All through the day under the house is this great cool air supply. My house has from 50cm to 180cm of space under the floor which is a lot of cool air. So my question was simply “can we use the cool air under the house to cool the house during the day?”

The experiment

I met with my local Ventis rep Matt and we designed the system to get air from under the house instead of from under the eaves. It was then passed through the filters so that we had fresh air coming into the house. So it was very close to a standard installation, but with the cooler air coming from under the house instead of from under the eaves.



The damp smell from under the house wasn’t removed with just the standard filter. The filter is able to remove the mould spores, but not the odour. So while we experienced the health benefits of no spores, we still had a house that smelt damp at times.

The solution to this problem is to use a carbon filter with the normal filter to absorb the smell. So while it was an initial inconvenience it wasn’t an impossible hurdle to overcome.

It got hotter

What did kill the experiment was the fact that overall the house became hotter. I think I can understand why…

During the day when the temperature in the house started to rise, the Ventis system realised that there was cool air to be used and started to use the cool air from under the house. The problem is that the air under the house had to be replaced and it was replaced by…the hotter outside air. So during the day what I was actually doing was slowly heating up under the house.

But under the house is part of the house so what I was actually doing was increasing the heat of the house as a whole.

And at the end of the day, when there was a nice breeze outside, it wasn’t blowing under the house. So there was nothing to cool it down rapidly at the end of the day. So at the end of the day when a normal Ventis system would start to work, we were restricted.

And more humid

And finally, because the air under the house is more humid than outside air, we were pulling in air with a higher moisture content. So not only were we experiencing warmer temperatures, the house was humid.


The final outcome was very simple, Matt came back and moved the intake to under the eaves. Now the system works as originally designed.


1. Don’t use the under floor air to cool the house. Ideally I should just try and build a room down there (the infamous pool room) but that’s not going to happen.
2. Do consider active ventilation under the floor for winter.

Thank you to Ventis

I like to use shocking titles to get attention and “Ventis Experiment a Failure” I think should have got your attention. Chances are you want to know if Ventis is worth buying and are after a failure story.

Well, here’s the failure story and it’s about how they worked with me to experiment. It was a win/win (ultimately) for both of us – they got to try a new approach to their system and I got to test my theories. In the end we know that it’s not possible and that their existing arrangement is very good.

So thanks to Matt and the team at Ventis. As summer is kicking in, we are enjoying the system as it was intended.

And I recommend the system.