Blower Door Tests: How We Prove Airtightness
- sheenakerai
- May 20
- 3 min read
When it comes to making your home energy-efficient and comfortable, airtightness plays a crucial role. Air leaks can cause drafts, increase heating costs, and even lead to moisture problems. But how do you know if your home is truly airtight? That’s where blower door tests come in. This method provides a clear, reliable way to measure how well your home holds air, helping you identify leaks and improve your living space.
What Is a Blower Door Test?
A blower door test is a diagnostic tool used to measure the airtightness of a building. It involves mounting a powerful fan in an exterior door frame. The fan either pulls air out of the house or pushes air in, creating a pressure difference between inside and outside. This pressure difference forces air to flow through any gaps or cracks in the building envelope.
By measuring the airflow needed to maintain this pressure difference, the test quantifies how much air leaks through the building envelope. The lower the airflow, the tighter the building is. This test is widely used by builders, energy consultants, and homeowners to assess and improve home performance.
Why Airtightness Matters for Homeowners
Many homeowners underestimate the impact of air leaks. Even small gaps around windows, doors, or electrical outlets can add up to significant energy loss. Here’s why airtightness matters:
Energy savings: Reducing air leaks lowers heating costs by preventing warm air from escaping.
Comfort: Airtight homes maintain a more consistent indoor temperature and reduce drafts.
Indoor air quality: Controlling air leaks helps manage moisture and reduces the risk of mould growth.
Durability: Preventing unwanted air movement protects building materials from damage caused by moisture.
A blower door test gives you a clear picture of your home’s airtightness and points out where improvements are needed.
How the Test Works Step-by-Step
Preparation
Before the test, all exterior doors and windows are closed. Interior doors remain open to allow air to flow freely inside the house.
Setting up the fan
The technician installs the blower door fan in an exterior door frame. The fan is connected to a pressure gauge and airflow meter.
Creating pressure difference
The fan runs to either depressurise or pressurise the home, usually by 50 pascals (a standard pressure difference). This simulates a strong wind blowing against the house.
Measuring airflow
The equipment measures how much air the fan must move to maintain the pressure difference. This airflow rate corresponds to the amount of leakage in the building envelope.
Locating leaks
While the fan runs, the technician may use smoke pencils, infrared cameras, or thermal imaging to find specific leaks around windows, doors, vents, and other areas.
Reporting results
The test results include a leakage rate, often expressed as air changes per hour at 50 pascals (ACH50). Lower ACH50 values indicate better airtightness.
What to Expect During a Blower Door Test
The test usually takes about one to two hours. It is non-invasive and does not damage your home. You may notice a strong wind noise from the fan and some pressure differences inside the house, which can make doors harder to open or close during the test.
Technicians will explain the results and recommend areas to seal or improve. Common fixes include weatherstripping doors, sealing gaps around windows, adding foam sealant around plumbing penetrations, and insulating loft hatches.
How Airtight Should Your Home Be?
Building regulations and energy programs set different airtightness targets depending on climate and building type. For example:
New homes typically achieve an ACH50 between 4 and 7.
Passivhaus standards require an ACH50 of 0.6 or less, which is extremely tight.
Older homes often have ACH50 values above 10, indicating lots of leaks.
If your home has a high leakage rate, a blower door test helps prioritise sealing efforts to improve comfort and reduce energy bills.
Benefits of Airtightness Testing
Even if your home is new or recently renovated, airtightness can degrade over time due to settling, renovations, or wear and tear. Blower door tests can:
Verify the effectiveness of air sealing work
Identify new leaks before they cause problems
Help maintain energy efficiency and indoor comfort
Final Thoughts on Blower Door Tests
A blower door test is a straightforward, effective way to prove your home’s airtightness. It provides measurable data that helps you understand where air leaks occur and how to fix them. For homeowners, this means better comfort, lower energy bills, and a healthier living environment.
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