Blower Door Testing Services

Blower door testing seals a building, runs a calibrated fan to hold it at a reference pressure, and measures the airflow needed to maintain that pressure — quantifying exactly how much air leaks through the envelope. dL Flow Tech is an independent, NEBB-certified firm performing commercial building air-tightness testing across the Hudson Valley since 1982, documented to the standard your energy code or commissioning scope requires.

What is blower door testing?

A blower door test measures the air-tightness of a building's envelope — its walls, roof, foundation, windows, doors, and every penetration through them. A calibrated fan is mounted in an exterior opening and used to pressurize or depressurize the building to a reference pressure (commonly 50 pascals). The airflow the fan must move to hold that pressure equals the air leaking through the envelope, reported as CFM50 and often normalized to the building's surface area or expressed as air changes per hour.

Uncontrolled envelope leakage drives heating and cooling loads, undermines comfort near the perimeter, carries moisture into wall assemblies, and makes a building harder to pressurize and ventilate correctly. Testing turns "the envelope seems tight" into a measured number you can hold a project to.

Why commercial blower door testing matters

• Energy code compliance. The commercial energy code sets a whole-building air-leakage limit, and on many projects the only way to demonstrate compliance is to test. A common commercial target is on the order of 0.40 CFM per square foot of envelope at 75 Pa.
• HVAC load and equipment sizing. A leaky envelope adds heating and cooling load the mechanical system has to chase. Verifying tightness protects the design assumptions the equipment was sized to.
• Comfort and the perimeter. Drafts, cold perimeter zones, and rooms that won't hold temperature near exterior walls are often envelope-leakage problems, not HVAC problems.
• Moisture and durability. Air moving through wall assemblies carries moisture that condenses inside them. Air-barrier testing is as much about protecting the building as saving energy.
• Pressurization and IAQ. You can't reliably pressurize or ventilate a building whose envelope leaks unpredictably. Tightness is the foundation the mechanical design sits on.

Where buildings leak

Envelope leakage concentrates at transitions and penetrations — the places where one assembly meets another or something passes through the air barrier:

• Assembly transitions — wall-to-roof, wall-to-foundation, and floor-line joints.
• Penetrations — pipes, conduit, ductwork, and structural members passing through the air barrier.
• Windows, doors, and curtain wall — the seal between the frame and the rough opening.
• Rooftop curbs and service entries — where equipment, drains, and utilities break the plane of the enclosure.
• Air-barrier discontinuities — spots where the membrane or sealant was missed or damaged by later trades.

The standards behind the test

Commercial air-tightness testing follows recognized methods. ASTM E779 is the long-standing single- and multi-point fan-pressurization standard; ASTM E3158 covers large-building testing with multiple fans. The commercial IECC and ASHRAE 90.1 set the air-leakage requirements, and federal work — including U.S. Army Corps of Engineers projects — carries its own tighter air-barrier requirement (on the order of 0.25 CFM per square foot at 75 Pa).

How we run a blower door test

1. Confirm readiness and protocol. We verify the building is at the right stage — envelope and air barrier complete, intentional openings identifiable — and confirm which test standard and reference pressure the project requires.
2. Set up the fans and seal intentional openings. We mount the calibrated fan or fan array, and seal the openings the protocol specifies so the test measures unintended leakage.
3. Pressurize and depressurize. We run the building to the reference pressure in both directions, reading airflow across a range of pressures to build the leakage curve.
4. Locate leaks where that's in scope. When the goal is to fix leakage, we pair the test with leak detection — airflow at suspected locations, and where appropriate infrared or smoke methods.
5. Document the result. Measured leakage, test pressures, envelope area, the standard followed, and instrument calibration all go into a report that demonstrates compliance or flags the gap to be closed.

Blower door testing vs. duct leakage testing

A blower door test measures leakage through the building envelope. Duct leakage testing measures leakage out of the ductwork. A building can have a tight envelope and leaky ducts, or the opposite — and many commissioning scopes require both.

What your blower door testing report contains

A complete dL Flow Tech blower door report includes the instrument and fan calibration records, the test standard and reference pressure used, the building envelope area, the measured leakage (CFM50 and required units), the allowable or target value, the pass/fail result, and — where leak location was in scope — notes on where leakage was found.

Service area

dL Flow Tech performs blower door and building air-tightness testing from New York City north through the Hudson Valley to Albany — Dutchess, Westchester, Orange, Putnam, Rockland, and Ulster counties, the five boroughs, and the Capital Region. See our service-area pages for detail.

Frequently asked questions

How much does commercial blower door testing cost?

It's quoted per project — price depends on building size, the number of fans the envelope requires, and the standard you're testing to. A large building needing a multi-fan array is a different scope than a small one. Send your project details for a fixed-scope quote.

What air-leakage rate does my project need to meet?

That comes from your code edition and specification. Commercial energy codes commonly target around 0.40 CFM per square foot of envelope at 75 Pa, with tighter limits — roughly 0.25 — on federal and high-performance work.

Is a blower door test the same as a duct leakage test?

No. A blower door test measures leakage through the building envelope; a duct leakage test measures leakage out of the ductwork. They're different tests, and many commissioning scopes require both.

Can you test a large building that one fan can't pressurize?

Yes. Large buildings are tested with a multi-fan array sized to the building, following the large-building test standard. We size the array so the test is valid for the volume involved.

Can you also find the leaks, not just measure them?

Yes. When the goal is to reduce leakage, we pair the test with leak-location methods so the contractor knows where to seal, then retest to confirm the improvement.