The Blower Door Test

The blower door test is the most important tool for measuring home performance. The resulting measurement, defines craftsmanship and hidden quality in a home or building. Acheiving minimum levels is required to meet basic energy-efficient performance and important indoor-air quality standards like 62.2.

Blower door tests measure the airtightness of the Building Envelope

Thumbnail building envelope What is a Building Envelope?        

Blower doors: Top Metric for Quality

  • Indoor Air Quality
  • Energy Efficiency
  • Comfort
  • Durability 
Blower Door Test illustration Blower door test picture Blower door test diagram cutaway view.
Blower door: Fan with pressure gauge Attached inside door or window Results show how leaky or drafty the construction


This is a very simple tool for making homes better, now we just need to use it. International code requirements offer a bare minimum level of airtightness and performance, yet local codes still ignore it. Until builders consistently meet certain minimums, mandatory testing needs adoption and enforcement.

Airtightness, is currently the most cost-effective way to improve homes.


   ACH @ 50

ACH50 is the most common way of expressing airtightness measurements. Its the home's air changes per hour, at 50 pascals of pressure, the rough equivalent to a 20 mile per hour wind. This table is our interpretation of various code and certification levels for this measurement of hidden craftsmanship and quality.

Decisions about indoor-air quality, insulation and heating or cooling are dependent on this measurement. ACH50 of 2 should be a minimum goal in most temperate climates. Getting tighter could be more cost-effective compared to extra insulation or more efficient heating and cooling systems.


By building tight, we reduce sources of pollution from outside the building envelope and reduce risk of humid-air causing problems in hidden building cavities. This allows us to provide a safe location for the source of fresh, outdoor-air. Airtight homes need active, outdoor-air ventilation.

   Outdoor-Air Ventilation


With minimal effort, this custom home achieved a .282 ACH50. More benefits on blower door testing here:

 NC's tightest tested home?


Posted in Building Envelope

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