A blower door test uses a calibrated fan mounted in an exterior door frame to depressurize a home and measure how much air leaks through gaps, cracks, and unsealed penetrations. It's one of the core diagnostic tools a home energy professional uses during a home energy audit, and it's often required for building code compliance, weatherization programs, and some rebate applications.
How the Test Works
A blower door consists of a fan mounted in a temporary frame that seals into an exterior doorway, along with a pressure gauge and manometer. The technician closes windows and interior doors, runs the fan to depressurize the house to a standard pressure (commonly around 50 Pascals), and measures how much air the fan has to move to maintain that pressure. The more air the fan has to pull, the leakier the house.
Results are typically reported as CFM50 (cubic feet per minute of airflow at 50 Pascals of pressure difference) and are often normalized against the home's volume or square footage to produce an air changes per hour (ACH50) figure, which allows comparison against code targets or past performance.
While the fan runs, the auditor often uses a smoke pencil, infrared camera, or simply their hand to locate specific leak points — around window and door frames, attic hatches, recessed lighting, plumbing penetrations, and where walls meet foundations. This turns a single number into an actionable list of air-sealing priorities.
What the Results Mean
There's no single "pass" number that applies everywhere — target leakage rates vary by climate zone, home age, and which energy code or program is being referenced. In general:
- Older, leakier homes often show higher ACH50 numbers, reflecting years of settling, gaps around trim, and construction methods that didn't prioritize air sealing.
- New construction in many jurisdictions must meet a maximum ACH50 target set by the locally adopted energy code, so a blower door test is often a required inspection step before a certificate of occupancy is issued.
- A single number in isolation is less useful than a before-and-after comparison — many auditors run the test again after air-sealing work to demonstrate improvement.
For general background on how a blower door test fits into a full home energy assessment, the DOE's home energy assessment guidance outlines the typical components of a professional audit, including diagnostic testing like this.
Why It's Part of a Home Energy Audit
Air leakage is one of the largest — and most fixable — sources of energy loss in many homes. A blower door test gives a home energy professional an objective, repeatable measurement rather than a guess, which matters for a few reasons:
- It quantifies the problem. "This house feels drafty" becomes a specific CFM50 number that can be tracked over time.
- It helps prioritize spending. Combined with an infrared scan or manual leak-finding, it directs air-sealing dollars toward the leaks that matter most rather than cosmetic fixes.
- It's often required for verification. Weatherization assistance programs, some utility rebates, and HERS ratings typically require a blower door test as documented evidence of performance, not just a visual inspection.
- It's a safety check, too. Extremely tight homes can raise combustion safety and indoor air quality concerns, so results sometimes prompt a follow-up combustion safety test or a recommendation for mechanical ventilation.
What a Blower Door Test Typically Costs
A standalone blower door test often runs $150–$400, while it's frequently bundled into a full home energy audit priced from a few hundred dollars up to $600 or more. Cost drivers include:
- Home size — larger or more complex floor plans take longer to seal off and test.
- Whether it's standalone or bundled with a broader audit that also includes duct testing, insulation assessment, and combustion safety checks.
- Retest requirements — some programs require a post-work retest to confirm improvement, which adds to total cost.
- Local labor rates and travel distance for the technician.
How to Choose and Verify a Home Energy Professional
Not everyone who owns a blower door is equally qualified to interpret the results or recommend fixes. Before hiring:
- Verify certification directly. Look for BPI certification through the BPI contractor locator or a RESNET HERS rater credential through the RESNET HERS rater directory — both organizations train and certify professionals in diagnostic testing including blower door use.
- Ask what equipment and standard they use — reputable auditors follow standardized test protocols (such as those referenced by RESNET or ASTM) so results are comparable and defensible.
- Ask for the full report, not just a pass/fail statement — a useful report includes the CFM50/ACH50 numbers and specific leak locations found.
- Confirm whether a retest is included if you plan to do air-sealing work afterward and want to measure improvement.
- Check licensing and insurance as appropriate for contractors doing work in your home, in addition to certification.
This site is an independent directory built from public, source-backed records — it does not certify, endorse, or perform work on behalf of any listed professional. Always verify credentials directly with BPI, RESNET, or the relevant certifying body before hiring.
Do I need to leave the house during a blower door test?
No, but you'll need to close exterior doors and windows, and the technician will ask you to leave certain interior doors open or closed depending on the test setup. It's a quick, non-invasive process, typically taking 30–60 minutes.
Can a blower door test damage my home?
No. The fan depressurizes the house within a standard, controlled range and does not create unsafe pressure differentials when performed correctly by a trained professional.
How often should a blower door test be repeated?
There's no universal schedule — many homeowners get one as part of an initial audit and again after completing air-sealing work. Some programs or rebates specify their own retest timing requirements.