How to read a blower-door test report

The test measures the house under an imposed pressure

A blower door uses a fan temporarily installed in an exterior doorway to create a controlled pressure difference. The equipment measures the airflow needed to maintain that difference. It helps assess leakage through the building enclosure, which separates the tested space from its surroundings.

PNNL's enclosure leakage guide describes the test and commonly reported units. The result is not a direct reading of the air exchange that occurs all day in normal weather. Ask the tester to explain the test boundary and how the number will guide improvements to your particular house.

enclosure leakage guide · Source checked 2026-09-07

Understand CFM50 and ACH50

CFM50 is the airflow in cubic feet per minute at a 50-pascal test pressure difference. ACH50 expresses that airflow as air changes per hour relative to the tested enclosure volume. It is calculated as CFM50 multiplied by 60, divided by volume in cubic feet.

PNNL's calculation demonstration explains this conversion. For an illustrative house with 2,000 CFM50 and a tested volume of 20,000 cubic feet, the calculation is 2,000 × 60 ÷ 20,000 = 6 ACH50. That is an example of the arithmetic, not a target for your home or a measured result from a Temperaly customer.

calculation demonstration · Source checked 2026-09-07

Check the volume and boundary assumptions

Ask which spaces were included in the reported volume: the basement, an attic conversion, a connected addition, or another enclosed area may affect it. Different boundaries can make two reports look different even before any sealing work occurs.

In an attached home or apartment, ask how leakage to neighboring spaces was handled. A basic result should not be assumed to describe outdoor leakage alone. Have the tester explain whether additional testing is needed for the question you are trying to answer. Keep sketches or descriptions of the tested enclosure with the report, especially when comparing results across a renovation.

Turn one number into an actionable record

Use the following checklist when arranging the assessment. The most useful package combines the measurement with findings and a repair scope.

If a report says “pass,” ask which code, program, or agreed project criterion it refers to. An existing home, a permitted alteration, and a voluntary certification may have different requirements. Avoid using an online national threshold as a substitute for the applicable local one.

A leakage result does not answer every comfort question

The test does not directly measure insulation quality, room heating loads, moisture sources, or HVAC distribution. Additional inspection and measurements may be needed. Infrared images can be useful under appropriate conditions, but ask how an apparent temperature pattern was interpreted and verified.

For air escaping from ducts, use the separate duct-leakage test guide. A tight house can still have poor bedroom airflow, and sealed ducts can still be located within a leaky house. Naming the system being tested prevents one report from being treated as an answer to both problems.

Pair air sealing with an indoor-air plan

Reducing uncontrolled leakage changes how air moves through the home. EPA's weatherization guidance identifies ventilation, moisture, and combustion safety as part of responsible retrofit work. Tell the assessor about fireplaces, fuel-burning equipment, existing exhaust systems, and known damp areas before testing.

Have a qualified tester prepare the home and determine whether any conditions prevent the test. After sealing, ask how outdoor-air ventilation and relevant safety checks will be addressed. A lower ACH50 is a measurement outcome; comfortable, well-ventilated operation requires the rest of the plan too.

weatherization guidance · Source checked 2026-09-07

Choose the assessment around your decision

If you are planning a renovation, ask for testing early enough to influence the work and again when comparable verification is possible. If the concern is one drafty room, explain that symptom and ask whether blower-door-assisted investigation is appropriate. A utility energy program or qualified home-energy assessor may offer the relevant service.

Bring previous reports and upcoming project plans. Use our older-home upgrade sequence to connect the findings to insulation, ventilation, and HVAC decisions. Ask for a written explanation of what to do next, not just a number to file away.