Blower Door Testing in Maryland: How It Works & Why It Matters
The gold-standard diagnostic for finding hidden air leaks — and the first step toward a more comfortable, efficient Maryland home.
Book a $100 Energy Audit →Air Leaks Are Invisible — Until You Test for Them
A blower door test is a diagnostic procedure that measures how airtight your home is. A powerful calibrated fan is temporarily mounted in an exterior door frame and depressurizes the house, making every gap, crack, and penetration visible — either by the pressure difference itself or with a smoke pencil.
For Maryland homeowners, it's the most accurate way to understand why your home is drafty, why your heating bills are high, or why some rooms are never comfortable. It's also a required step for BGE and PEPCO rebate-eligible work through the Home Performance with ENERGY STAR program, and a core part of every Leonard Home Performance energy audit.
How a Blower Door Test Works
The test takes about 20–30 minutes and follows a consistent protocol used by BPI-certified analysts nationwide.
Prepare the House
All interior doors are opened, exterior doors and windows are closed, and combustion appliances (furnaces, water heaters) are temporarily turned off to avoid interference with the pressure measurement. Fireplace dampers are closed as well — if left open, the depressurization can pull soot and debris down into the home.
Mount the Blower Door Fan
A canvas frame with a calibrated variable-speed fan is installed in a doorway — usually the front door. A pressure gauge (manometer) is connected to measure airflow and indoor-to-outdoor pressure difference.
Depressurize the Home
The fan draws air out of the house, creating a 50 Pascal pressure difference (about 20 mph wind pressure) across the building shell. Outside air rushes in through every gap and crack in the envelope.
Measure the Airflow (CFM50)
The software records how many cubic feet of air per minute (CFM) the fan must move to hold 50 Pascals of pressure. The higher that number, the leakier the house. This figure is then converted into an ACH50 rating — the standard metric for airtightness.
Locate the Leaks
With the fan running, the auditor walks the home using a smoke pencil, thermal camera, or simply a hand. Air rushing in from outside is easy to feel at attic hatches, recessed lights, plumbing penetrations, rim joists, and other common leak locations.
Understanding Your ACH50 Score
ACH50 stands for Air Changes per Hour at 50 Pascals. It tells you how many times per hour all the air in your home would be replaced by outdoor air if it were constantly under 50 Pascals of pressure. Lower is better.
What a Blower Door Test Reveals
A numeric ACH50 score alone is just a starting point. The real value is that it guides where to look — and helps prioritize which leaks are worth sealing. Most of the biggest leaks are driven by the stack effect, the physics that pulls warm air up and out through the attic while cold air is drawn in at the foundation.
Attic Bypasses
Gaps where interior partition walls, plumbing chases, and wiring run up into the attic are often the biggest single source of air leakage in older Maryland homes.
Recessed Lighting
Older "can lights" are essentially open holes in the ceiling. Under depressurization, cold attic air rushes in through every fixture.
Rim Joists
The band of framing at the top of your foundation wall is notoriously leaky — and cold in winter. Often missed during basic insulation work.
Attic Hatch
An uninsulated, unsealed attic hatch can leak as much air as a window left open an inch — year round.
Plumbing & Wiring Penetrations
Every pipe and wire that passes between conditioned and unconditioned space is a potential air leak that compounds over the entire house.
Duct Leakage
Ducts running through unconditioned attics often leak conditioned air directly into that space — a major efficiency loss the test can help quantify.
Why the Blower Door Test Matters for Maryland Homes
Maryland's climate is demanding in both directions — humid summers and cold winters — which makes air sealing especially important. Here's why the test matters beyond just a number:
It Guides Smarter Spending
Without testing, contractors guess where to air seal. With a blower door, we know exactly which areas are leaking and how much — so your money goes where it makes the biggest difference.
It's Required for BGE & PEPCO Rebates
BGE and PEPCO require a pre- and post-improvement blower door test for projects enrolled in the Home Performance with ENERGY STAR program. The test verifies that the work actually reduced air leakage — and unlocks rebates of up to $10,000 for air sealing and insulation (or up to $15,000 when paired with electrification upgrades like a heat pump water heater). See our 2026 BGE & PEPCO rebates guide for the full breakdown.
It Explains Comfort Problems
If your second floor is hot in summer or your home is drafty despite new insulation, a leaky building envelope is almost always the cause. The blower door puts a number on the problem — and points to the solution.
It Verifies the Work Was Done Right
After air sealing, we retest to confirm the ACH50 score dropped. This before-and-after comparison is the proof that the project delivered real results — not just a promise.
Can a Home Be Too Tight?
It's a fair question — and the short answer is: not likely in an existing Maryland home. Virtually every older house we test is far leakier than ideal, and professional air sealing brings them closer to code minimums, not past them.
That said, the concern isn't without merit. As homes get tighter, natural air exchange decreases. In a very tight home — typically new construction below 3 ACH50 — mechanical ventilation becomes important to maintain healthy indoor air quality, manage humidity, and remove pollutants that would otherwise dilute on their own.
For most existing homes in the Baltimore area, air sealing gets you to 4–6 ACH50, which is a significant improvement without requiring any ventilation upgrades. But if you're pursuing a deep energy retrofit or your home already tests tight, whole-home ventilation is the logical next step. Learn more about whole-home ventilation →
Common Questions About Blower Door Tests
Learn More
The blower door test is just the starting point. Here's what typically comes next:
Sources & References
This article references the following authoritative sources on blower door testing, BPI protocol, and Maryland's utility rebate programs:
- Baltimore Gas & Electric (BGE), "Home Performance with ENERGY STAR® Program" — bgesmartenergy.com
- PEPCO, "Home Performance with ENERGY STAR® Program — Maryland" — homeenergysavings.pepco.com
- U.S. ENERGY STAR, "Home Performance with ENERGY STAR" program overview — energystar.gov
- Building Performance Institute (BPI), "Building Analyst Professional" standard — bpi.org
- U.S. Department of Energy, "Blower Door Tests" — energy.gov
- EmPOWER Maryland, program information — energy.maryland.gov
Rebate amounts, eligibility requirements, and program terms are set by the utilities and the Maryland Public Service Commission, and are subject to change. Verify current details with BGE or PEPCO before committing to work.
Ready to Find Out Where Your Home Is Leaking?
A $100 energy audit includes a full blower door test, insulation inspection, combustion safety check, and a written report — everything you need to qualify for BGE and PEPCO rebates.