Air Tightness Testing Example

Low Carbon Box provide an overview of an air tightness testing example so you can see what to prepare for. The process is straightforward, but sometimes a bit of preparation before the test and care on site during the test can make a difference.

Stage 1 – Information prior to the air tightness test

The air test result is given as:

m3/hr/m2 at 50 Pa

So this is the volume of air leakage (m3) over a period of 1 hour per 1m2 of surface area of the building. This is carried out with a pressure difference of 50 Pa (Pascals)

We will need the following to be able to determine the volume of the building and the internal surface area of the building:

  • Floor plans
  • Sections through the building
  • Elevations

The air tester can the determine the total volume (m3) and surface area (m2). We used Sketchup for more complex models to ensure we get this accurate:


Stage 2 – Checklist

Low Carbon Box will issue a checklist to help gain important information about the property and also allow you to check that certain elements of the building have been sealed. Example below:


The earlier you appoint an air tightness testing consultant, the better so you can deal with this issues before completing the building. Such as ensuring the soil stack in the boxing is sealed at both ends to prevent air leakage up into the roof space.

Stage 3 – Setting up the air tightness test

When we arrive, we will check trickle ventilators are closed and tape up ‘controlled ventilation’ such as extraction fans, cooker hoods and wall grills.

We will fit the door kit and hang the fan as indicated in the video below:

Stage 4 – Turn the fan on

We would then turn the fan on and check for and obvious leaks or draughts in the property. You can see in the following video how the fan (hinged at the top) pulls into the property as the pressure difference increases as the fan extracts the air out of the dwelling:

Stage 5 – Pre-test leak detection

While the fan is running, we will walk around for any obvious signs of leaks. You can use smoke guns or pipettes, thermal imaging camera (when colder outside than inside) or even this simple thermal leak detection unit to spot where cooler air leaking in while the fan is on. You can see in this example, the room temperature is >18oC but cools down as we move it across the toilet drainage connection indicating cooler air inflow:

A simple way of detecting which room has a leak is (while the fan is running), remove the door stop and see if it will close on its own. See example below:

You can see the door actually slams. This indicates air being pulled through the kitchen and with a further inspection, we find the soil pipe boxing is not sealed correctly and air is being pulled down from the ventilated roof space.


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