Negative Pressure FAQ

What is negative pressure?

Negative pressure can occur when there isn’t enough ventilation in the home and an exhaust fan is operating. Essentially, it has the effect of drawing air from any external opening in a house, including gas appliance flues and chimneys. This creates a problem with the operation of an open-flued gas heater – and particularly a faulty one – because it means that dangerous gasses, such as carbon monoxide, can be drawn into living spaces via the gas appliance flue or chimney.

Watch the below video to learn more about negative pressure



How do gas fitters test for negative pressure?

When the gas fitter attends a property that has an open flued gas appliance they are legally obligated to test for negative pressure. This is carried out by simulating a scenario that is most likely to identify the presence of negative pressure. 

The gas fitter will start by closing all the external doors and windows in the property. All extraction devices such as range hoods and exhaust fans are then turned on. Internal doors to rooms that contain extraction devices are left open. The gas fitter will then conduct a 'smoke test' adjacent to the appliance.

To pass the test the smoke created needs to travel upwards or towards the flue system in a steady upward stream. If the smoke draws away from the appliance and towards the extraction devices, then it is determined that the property is prone to negative pressure and additional ventilation is required. 

How is negative pressure rectified?

Sufficient ventilation is required to allow the pressure in the property to be equalised. The gas fitter will determine the size & location of the ventilation required and a quotation for the required work is then issued. 

When the vent required to balance the negative pressure is greater than 50000mm² we will not quote and recommend a new room-sealed or power-flued appliance that is not affected by negative pressure. We do not quote for large vents as this can adversely affect heating and cooling in the property and allow unnecessary drafts.

What are the property owner's obligations when negative pressure is found?

Each time negative pressure is found, the gas fitter completing the service has a legal obligation to report the finding to the Victorian Builders Authority (VBA). The VBA will then keep these properties on file and follow up with the owner to ensure the correct steps have been taken to have the problem rectified.




Related articles & additional resources:

Negative pressure environment


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