• Sean

Evaluating a house after a failed blower door test

Updated: May 2, 2019

Failing blower door tests is extremely common in Tennessee. Its important to check these places if you fail.


The blower door test has come in and the house has an ACH50 (air changes per hour at 50Pa of pressure) higher than 7, which is the maximum allowed by most local TN codes (and is based on a rapidly aging recommendation from IECC 2009).  

What do you do to get the house up to snuff?  

How can we quickly identify areas for improvement and get some of the most accessible and largest holes in the building envelope sealed and fixed?

The easiest way to do this is for it to be done while the test is on-going, and for the testing crew to conduct some inquiry while the house is depressurized.  At this point, the air leaks are going to be most apparent and most easily recognizable with the proper equipment. 

The best tools for the job:

  • Thermographic camera

  • Smoke pens (for those a bit more old school or looking to validate what the FLIR shows you)

  • Simple painter’s tape to quickly test sealing opportunities.

  • Blower door

Where to look for failures?

A pressure barrier (this is where the airtight envelope exists) has predictable failure locations where we should look for failures first:  

  • Are all exterior doors and windows weather sealed - this might not be a huge amount of leakage but is often the easiest to fix if not yet done.

  • Any place there is a penetration through the top plate into the attic (think plumbing, electrical, recessed lighting, ductwork).  This might be hard to get to now know that some thick attic insulation is already in place. Attic penetrations are usually the worst offenders here, though.

  • Attic knee walls, especially at the bottom of the connection joint where airflow might not be impeded and sealing might have been readily overlooked.

  • Access doors into wall or attic crawl spaces from the conditioned space, often also part of a knee wall itself.  These can be difficult to seal, and need extra attention.

  • Sealing electrical outlet and light-switch cover-plates.  These little guys can really add up (especially on exterior walls), and should be sealed with spray foam, not gaskets (which can easily be damaged)

  • Any other places where there may be breaks in the exterior plane and odd joints or extrusions in the exterior surface of the building.  These are natural places for improper sealing during construction, and can be targets for an inquiry with a thermographic camera and smoke testing.

  • Are water traps filled with water? For example, toilets Toilets, etc, without water in the pipes can also contribute to an excessively high leakage rate, and should be filled before a new test is done.

  • Ductwork - checking for disconnected supply ducts or excess leakage in ductwork connections. These will be identifiable through a duct leakage test, and will also contribute to a failing whole house infiltration test with a blower door.

Checking these ares for leakage should identify where excess infiltration is occurring, and help the crew identify areas in need of special attention.

However, they also serve as great set of areas to focus on during construction, which can to prevent a failed test from the outset.   

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