Have you been told that you need a blower door test? 

If you have it’s probably because it is required by the building code official for new construction or a major renovation. It can also be a key component of an existing building energy audit, an energy model required for tax incentives or appraisals, to optimize energy or ventilation performance, or to solve ongoing problems in an existing building. in practice, every building is different. We’ve learned a lot over the past ten years doing 100’s of blower door tests for all of these reasons, and hope the following helps demystify the process.

Why is a blower door test important?

Blower door testing is the only way to accurately determine building tightness. Gone are the days of ‘rule of thumb’ assumptions. The 2015 and 2018 Energy Conservation Building Code in Virginia requires this to be be < 5 air changes per hour (ACH) for the conditioned building enclosure. But that’s just the beginning – while predicted building tightness is used to size heating and cooling systems, the verified ‘actual’ building tightness is the only way to accurately size ventilation systems according to the companion Mechanical Code to keep indoor air fresh and prevent moisture problems. As is often stated in building performance circles: “Build it tight. Ventilate right”. Both statements are equally important and rely on each other, which is why we add “Everything is connected”.

What is a conditioned building enclosure?

All buildings essentially have six sides: top, bottom, and north, east, south and west walls. These surfaces and edges are where water, air, vapor, and thermal layers work together to keep unwanted air, heat, cold, water and moisture out. Gaps in the building enclosure can be a bigger problem than just higher energy bills. A tight, well-performing building enclosure has very few leaks. It is essential to know if attics, basements or crawlspaces are inside or outside the building enclosure, as this can affect the results dramatically.

What is a blower door test?

 A blower door test uses a large fan mounted in an air tight canvas ‘door’ that is connected to a gauge (a manometer) that can measure the airflow through the fan as well as the pressure difference between inside and outside while the fan is running. This information is combined with the building enclosure area and volume to calculate resulting air tightness in air changes per hour. Along with number of bedrooms and occupancy, measured air flows at exhaust fans and some other facts about the building, test results are also used to calculate optimal fresh air ventilation required by the Mechanical Code, specifically ASHRAE 62, to keep occupants healthy and the building in good condition.

How can I make sure I pass the blower door test?

In new construction we recommend a tried and true three step process. 

  1. Have a plan for air sealing and insulating while at the same time controlling vapor transmission. This is ideally clearly stated in the construction drawings. We’ve assisted designers and contractors alike to get this plan right from the beginning to save time and money.
  2. During construction, do periodic checks to make sure the strategy is followed for every trade. Designate one person to verify that air sealing measures are properly completed. A quick mid-construction “Pre-Drywall Verification” with a building scientist helps many of our builder clients to ensure a successful final blower door test.
  3. Final Blower Door Testing is one of the last things to occur in the construction process, so failing it can be expensive. Ideally this occurs after all appliances, caulking and finishes are installed, and all systems are operational.

What if I fail the blower door test?

If a blower door test is unsuccessful on the first try, we attempt to discover the larger leaks that are causing a problem. When there isn’t a good record of where the leaks may be, we use infrared and zonal pressure testing to help find them. Then we typically recommend air sealing measures and come back to retest after they’ve been completed. We’ve never seen a building fail so far when Pre-Drywall Verification recommendations were followed by the builder.

Can existing buildings pass a blower door test.        

It’s not as much about ‘passing’ as knowing for existing buildings, which are usually (but not always!) leakier then new construction. They are typically are not required to meet building code targets unless a major renovation, an energy retrofit or addition occurs. Knowing actual building tightness is essential because assumptions can lead to costly mistakes. If you are planning any changes to equipment, appliances, insulation or thinking of renovating, a blower door test is a foundational piece of information to define needed scope of work and to lower the risk of wasted money – or worse.

Who gets the blower door test results?

In new construction, blower door tests should be distributed to four people:

  1. The General Contractor keeps this on hand for warranty purposes and proof of building tightness at construction completion. Pre-DrywallVerification records are also kept.
  2. The Code Official: A Blower Door Test Affidavit is provided to the Code Official and is usually the last step in securing the Certificate of Occupancy. This document is usually kept with municipality real estate records.
  3. The HVAC Contractor: Blower Door Test results are an essential measurement for calculating ventilation requirements and the HVAC contractor is required to size this and calibrate ventilation according to ASHRAE 62.2 for homes. If a Mechanical Engineer designed the systems, send to them, as well.
  4. The Building Owner: Keeping Blower Door Results on hand will allow future upgrades to be based on verified data, rather than conjecture. Future blower door tests can also be compared to the original to optimize capital expenditures or solve building problems.

Are you ready to schedule a blower door test?

As you’ve probably gathered, it takes skill and experience to properly complete a blower door test, so be sure to use a BPI or RESNET certified tester. Send us any additional questions you may have. And don’t forget: Build it tight. Ventilate right. Everything is Connected.


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