Small cracks. Big energy loss. Every house leaks air somewhere, and a blower door test is the fastest, most reliable way to find those leaks so you can stop wasting money and make your home genuinely comfortable.
Introduction
Hidden gaps and cracks let conditioned air slip away and let outside air sneak in. Left unchecked, those leaks drive up heating and cooling bills, create drafts, and complicate moisture control. A blower door test is like a check‑up for your home’s envelope: it measures how airtight your house is and points to exactly where fixes will do the most good.
This guide explains how a blower door test works, what the numbers mean, how much testing typically costs, and why the test is often the smartest first step before spending money on insulation, windows, or HVAC upgrades.
What Is a Blower Door Test?
A blower door test is a diagnostic procedure performed by a certified energy technician as part of a home energy audit. It measures how much air leaks through your home’s building envelope — the walls, windows, doors, attics, and crawlspaces that separate inside air from the outside.
During the test, a powerful fan is temporarily mounted in an exterior doorway. By pressurizing or depressurizing the house and measuring the airflow required to maintain a set pressure, the technician calculates the household’s airtightness as ACH50 (air changes per hour at 50 pascals). Lower ACH50 equals a tighter, more efficient home.
Blower door tests are commonly used for:
- New construction (to meet energy codes)
- Energy retrofits (to identify air‑sealing needs)
- Certification programs like ENERGY STAR and LEED
Sources: U.S. Department of Energy, ENERGY STAR, Building Performance Institute (BPI).
How a Blower Door Test Works
Step 1 — Setup
The technician installs a frame and a calibrated fan in an exterior door. Windows and exterior doors are closed while interior doors are left open so air can move freely through the house. Pressure sensors and digital gauges are set up to log how the home reacts when pressure changes.
Step 2 — Testing Process
The fan depressurizes the home, which draws outdoor air through leaks. The technician watches the gauges and uses tools to find leaks, such as:
- Smoke pencils or incense to visualize airflow
- Infrared cameras to reveal temperature differences (where outside air is coming in)
- Anemometers and pressure sensors for precise readings
Readings are recorded in real time and used to calculate total leakage.
Step 3 — Analysis
The collected data produces the ACH50 number (air changes per hour at 50 pascals). That single metric describes how many times the entire indoor air volume would be replaced by outside air in one hour under the test pressure. Think of it as a “health score” for your home’s airtightness.
Analogy: A blower door test is a physical check‑up for your house — it shows where the building is losing energy and how urgently those leaks should be fixed. In fact, SmartWeatherize describes how blower door tests measure how much air leaks from your home in their explanation of how weatherization works.
Why Air Tightness Matters
Airtightness affects energy use, comfort, indoor air quality, and moisture control. Here’s how:
Energy Waste
Leaky homes let heated or cooled air escape, making HVAC systems work harder. The American Council for an Energy‑Efficient Economy (ACEEE) estimates that sealing leaks can reduce heating and cooling costs by 15–30%.
Comfort
Drafts, cold corners, and uneven temperatures are classic signs of air leakage. Tightening the envelope evens out temperatures and eliminates many of those annoying drafts.
Moisture and Mold Control
Uncontrolled airflow can carry moist outside air into assemblies where it condenses, promoting rot and mold. Better airtightness makes moisture control and dehumidification far easier to manage.
Environmental Impact
Sealing air leaks reduces wasted energy and the carbon emissions that come with it — a simple but meaningful step toward local and regional climate goals.
Sources: ACEEE, U.S. EPA (epa.gov).
Benefits of a Blower Door Test
- Identifies hidden air leaks in attics, crawlspaces, ducts, and around electrical boxes, so you aren’t guessing
- Improves energy efficiency by showing where sealing or insulation will have the biggest payoff
- Increases home comfort by reducing drafts and temperature imbalances
- Supports code compliance — many states now require testing for new construction energy codes
- Enables rebates and certifications — test results are often needed for ENERGY STAR, utility rebates, and federal credits
Blower Door Test Results Explained
The most important figure you’ll get is ACH50. Here’s a simple guide to interpret that number:
| Home Type / Efficiency Level | Typical ACH50 Value | Description |
|---|---|---|
| Older, leaky homes | 10–20 ACH50 | Major air leakage and energy loss |
| Average modern home | 5–7 ACH50 | Meets basic energy code requirements |
| ENERGY STAR certified | ≤ 3 ACH50 | Very energy-efficient and airtight |
| Passive House standard | ≤ 0.6 ACH50 | Ultra-tight building envelope |
Lower is better — but remember: very low ACH50 values mean you must manage ventilation intentionally (ERVs/HRVs) so occupants still get fresh, filtered air.
Cost of a Blower Door Test
Expect to pay roughly $300–$600, depending on region and house size. Many contractors bundle the blower door test with a full home energy audit (infrared scan, insulation inspection), which can offer better value.
Potential Savings
Fixing leaks identified during the test can typically cut annual energy bills by 15–30%, often translating to several hundred dollars saved per year.
Available Incentives
Puget Sound Energy (PSE): Weatherization rebates tied to completed energy audits.
Energy Trust of Oregon: Cash incentives for air sealing and insulation work.
Inflation Reduction Act (2024–2025): Federal tax credits for qualifying efficiency upgrades.
Sources: HomeAdvisor, EnergyStar.gov, PSE / Energy Trust of Oregon.
How to Prepare for a Blower Door Test
To get accurate, useful results, do these simple things before your technician arrives:
- Close all exterior doors and windows.
- Open all interior doors.
- Turn off HVAC systems and gas appliances.
- Seal fireplaces, chimneys, or wood stoves (so ash or drafts don’t affect the test).
- Remove or secure pets.
- Extinguish any pilot lights if the technician asks you to.
These steps help ensure consistent pressure and accurate readings during the test.
What Happens After the Test?
After testing, the technician will:
- Review your ACH50 result with you.
- Show leaks found on infrared scans or with smoke testing.
- Recommend targeted fixes like caulking, weatherstripping, duct sealing, or adding insulation.
- Advise about ventilation upgrades (ERVs/HRVs) if your home becomes very tight.
Pro tip: Airtightness is only half the equation — balanced ventilation is essential for healthy, comfortable indoor air.
FAQs About Blower Door Testing
- Q1: Do all homes need a blower door test?
- A: It’s most useful for older homes (to find leaks) and new builds (to verify compliance). If you’re planning major energy upgrades, include a blower door test so you can prioritize the work that will save the most energy.
- Q2: Will a blower door test damage my house?
- A: No — the test is safe and temporary. Trained technicians use controlled pressure changes and follow protocols to protect the home.
- Q3: How long does a blower door test take?
- A: Most tests take about 1–2 hours, depending on house size and whether the technician performs additional diagnostics like infrared scanning.
- Q4: What if my home is “too tight”?
- A: If ACH50 is very low, installing mechanical ventilation such as an ERV (Energy Recovery Ventilator) or HRV (Heat Recovery Ventilator) is the right move. These systems bring in fresh air without wasting heat.
Conclusion
A blower door test is one of the smartest early steps you can take to improve home performance. It pinpoints the leaks that cost you money and points you to the most cost‑effective fixes. Before you spend money on insulation, new windows, or an HVAC overhaul, run a blower door test and let data guide the decisions.
Small leaks add up to big energy waste — but a proper test shows you exactly where to act.
Next Steps for Homeowners
- Schedule a home energy audit with a certified technician.
- Seal the leaks the test identifies and add insulation where it will matter most, as recommended in SmartWeatherize’s Top Weatherization Techniques for Energy‑Efficient Homes.
- Apply for local rebates or federal credits to offset costs.
- Install balanced ventilation if your home becomes very tight.
- Monitor energy usage over time to confirm savings and comfort improvements.
Lily Strauss is an environmental and energy expert based in Boulder, Colorado, with a background in Environmental Science from Stanford and Energy Policy at a London College. She began her career in environmental consulting before moving into energy policy, contributing to major sustainability initiatives with NGOs and the U.S. Department of Energy. Currently a senior advisor at a global climate think tank, she focuses on energy equity and climate resilience. Outside of work, Lily enjoys rock climbing, photography, and urban farming, and is passionate about climate justice and youth education in sustainability.