Subfloor Ventilation Icon image with vents and air flowing

Sub Floor Ventilation Fans, Costs and Solutions

Subfloor Ventilation Cost
DIY Subfloor Ventilation Installation

Your sub floor, also referred to as the under floor space, may seem insignificant because it does not form part of your living room. However, the fact of the matter is that this space actually has a high impact on the quality of air you breathe in while you are indoors and may affect your health if your sub floor vents are insufficient.

Poor sub floor ventilation could lead to poor health for you and your loved ones. Additionally, it could cause damage to some parts of your home or commercial space that are susceptible to decay that do not have ventilation fans. This damage caused by the development of mould due to high humidity levels in the house. We at Mouldbuster will do everything possible to eliminate the stale and moist air from the subfloor using sub floor ventilation systems and fans to ensure that only fresh and dry air occupies that under floor space.

Ventilation showing air flowing in externally and flowing out through breathing vents on the sides of the house.

To achieve this, one of the following sub floor ventilation systems can be used:

Sub Floor Ventilation Exhaust System

The logic behind the exhaust system is that a greater quantity of stale air is sucked out of the underfloor space than the fresh air that is blown into it. In order to achieve this, only one fan is dedicated to the supply of fresh air, while two are required for the expulsion of the stale air through vents. The two are referred to as exhaust fans.

Nature abhors vacuum. Automatically, the vacuum conditions created when the stale air is continuously sucked out of the sub floor will be filled by fresh air from outside. This is also enhanced by the negative pressure that exists in the under floor due to the unequal movement of air. In the process of installing this system, the ventilation expert will determine the best place to vent out the damp air. This would typically be done through the lower part of the wall.

Sub-Floor Supply System

The sub floor ventilation system is the opposite of the exhaust system; instead of creating negative pressure, it creates positive pressure. A greater quantity of air is blown into the sub floor space, using mechanical ventilation kits which will, as a result, force the damp, moist out.

There are two supply fans that bring in the fresh and dry air from the outside, and only one exhaust fan that gets rid of the damp air. Ventilation kits are available or custom installation provided to help solve these problems. This is because the positive pressure will work to push out the dampness automatically. Some of the positive aspects of this system are:

  • It facilitates the drying up of damp or moist areas in the sub-floor area because dry air is constantly being blown over them. It is more effective than trying to force out the moist air from the damp surfaces
  • It creates an effective way to manage the odors and moisture that exist in the subfloor area, where the dampness is redirected outside the residential home. Caution needs to be taken however, to ensure that the escape vent is sufficient for the dampness to leave the sub-floor one one side or both this is not done, the dampness will end up rising into the home or commercial property.

Balanced Pressure System

Quite different from both the exhaust and the supply systems, as the name suggests, there is a balance between the two fans that work in this sub floor ventilation system. One of them creates positive pressure, and brings dry and fresh air into the underfloor ventilation space. The other one works using negative pressure and expels the same amount of stale or moist air from the under floor. It is balanced because the speed at which the air moves into and out of the sub-floor is the same. Both are considered mechanical ventilation systems.

There are some noteworthy advantages of this system:

  • Damp surfaces will eventually be dried up through the expulsion of moistness from the damp surfaces and the subsequent flow that is blown over them
  • The management of the stale smells and dampness is effective since the installation of the outlet through which this airflow is expelled is determined by you
  • The entire subfloor area will be managed by the system because the entry point into the sub floor area is at the extreme opposite of the exit point of damp air

Infographic: Sub Floor Ventilation Infographic discussing underfloor Balanced Pressure System, Exhaust System and Supply System.

Sub Floor Ventilation Sydney

Each of the subfloor ventilation fans have specific designs, shapes and sizes for your home. The kind of fan you will select depends on how big or small your under floor area is and what problems you need to solve. It will also depend on the materials which your house is made from, e.g. timber.

Fans usually have either the AC or EC motor for the subfloor ventilation system. The AC fans are set to run at one speed only, but are not noisy when running. On the other hand, EC fans have different speeds and are more efficient and less noisy than AC fans.

The subfloor fans should run during the day. Ventilation is drier during the day and the system’s noise will not be easily heard over typical daytime activities.

Once the installation of the sub-floor ventilation system is done, the high humidity levels in the under floor will only be brought to negligible levels after the system has run for twelve hours. After this initial set up and run time, you won’t need it to go on for such long hours. Four hours per day will be sufficient to keep the sub floor ventilation at its best, making the under floor space both fresh and moist-free.

Underfloor Ventilation Cost

A quality sub floor ventilation system with supply or exhaust fans for an averaged sized home around Sydney and in Australia should be around $2500 supplied, installed, including GST and 5 years warranty.


Sure.  Talk to us about supplying a sub floor ventilation kit including all required fans.

We service homes and businesses and commercial properties for high moisture in states Australia wide, including the New South Wales, Queensland, Australian Capital Territory, Victoria, Western Australia, South Australia and Tasmania.

Capital cities Australia wide include, Sydney, Canberra, Melbourne, Perth, Adelaide, Hobart and Brisbane.

Contact us, the sub floor ventilation and under floor ventilation fan experts, Mouldbuster on 1300 066 853 for the best advice on supply and exhaust underfloor fans and, to discuss your best options based on your budget to insure you have a healthy home. Contact Us today.