Blower Door Test

Leaky homes are hard to heat and hard to cool. Every home has air leaks, but the cumulative amount of leaks can vary widely based on the air sealing efforts. The only way to know whether your home is leaky or tight is to measure its air leakage rate with a blower door. A blower door is a tool which is comprised of a calibrated fan, a mounting system to attach the fan to an exterior door, and a manometer which measures pressure.

Many homeowners assume that gaps around windows and doors are responsible for most of a home’s air leaks. In fact, air leaks in the following areas are usually much more significant:

  • Basement rim joist areas
  • Holes cut for plumbing traps under tubs and showers
  • Cracks between finish flooring and baseboards
  • Utility chases
  • Plumbing vent pipe penetrations
  • Kitchen soffits
  • Fireplace surrounds
  • Recessed can lights
  • Cracks between partition top plates and drywall

An energy-efficient house must be as airtight as possible. There is no such thing as a house that is too tight. However, it’s also true that there is no such a thing as an airtight house. Every house leaks, and that’s why we perform blower-door tests — to measure a building’s leakage rate.

If you’re building a new home, the best time to conduct a blower-door test is after the home is insulated but before the drywall is hung. If the test reveals major problems, the leaks will be easier to fix at that point than later on.


What’s A Good Blower Door Test Number?
The metrics and math can get a little technical so let’s put them in context. Here’s a rough scale to compare your blower door test number to other standards:
10-20 ACH50 – Older homes, like living in a “barn”
7-10 ACH50 – Average new home with some air sealing but no verification and little attention to detail
7 ACH50 – OK infiltration level and the 2009 IECC energy code requirement
3-5 ACH50 – Good and achievable target for most new homes. The ENERGY STAR reference home is 5 ACH50 for climate zone 4 which covers DC, MD, VA and part of PA. The majority of PA is 4 ACH50 for the ENERGY STAR reference home.
3 ACH50 and lower – Tight home with great air sealing, and required by the 2012 energy code adopted in MD and coming to other jurisdictions soon.
.6 ACH50 – Super tight home and the Passive House standard.