Blower Door Test: Cost, Process and How to Read the Results

A blower door test measures how leaky your house is. A calibrated fan is sealed into an exterior doorway and pulls the house to a set pressure, usually 50 pascals. The test then records how much air the fan moves to hold that pressure. Expect to pay roughly $200 to $450 for a single-family home. The result tells you whether the building envelope is tight enough for code, comfort and lower energy bills, and where to seal if it is not.

This guide covers what the test measures, what happens on test day, what the numbers mean, what to do after a failed test, and how to plan for it whether you are building a new home or finishing a remodel or addition.

TL;DR

• A blower door test uses a calibrated fan in an exterior doorway to measure air leakage, typically at 50 Pa. Results are often reported as ACH50.
• Typical cost for a single-family home is $200 to $450, with an average around $325. Add-ons such as thermal imaging cost extra.
• On new construction, the final test happens after electrical, mechanical and plumbing work is finished. A mid-construction test before drywall is the cheapest time to fix leaks.
• A failed test is not a disaster. You find the leaks, seal them and retest. A tight house also needs planned mechanical ventilation.

Table of Contents

• What a blower door test is and what it measures
• How a blower door test works, step by step
• Blower door test for new construction
• Blower door test cost
• Blower door test results explained
• What happens if you fail
• Tight house, planned ventilation
• Blower door testing for remodels and additions
• Our perspective
• Planning an energy-efficient build or remodel with us
• FAQ
• Sources

What a blower door test is and what it measures

A blower door is a diagnostic tool: a powerful, variable-speed fan mounted in a temporary frame in an exterior door opening. According to the U.S. Department of Energy’s Building America program, the test measures a building enclosure’s air-leakage rate, and it can help locate the areas where air gets in and out.

The fan either pressurizes or depressurizes the house to a standard reference pressure, typically 50 pascals. The equipment measures how much airflow the fan needs to hold that pressure. The leakier the house, the harder the fan has to work.

Fifty pascals is a lot lower than it sounds. It is roughly like a steady 20 mph wind pushing on every surface of the house at once. The point is not to mimic daily weather. The point is to create a pressure strong enough, and repeatable enough, to compare one house with another or one test with the next.

Why leakage matters to homeowners

Uncontrolled air leakage can waste energy, trap moisture, cause health concerns and shorten the life of a structure, according to University of Minnesota Extension. In practical terms you feel it as:

• Cold floors and drafty outlets in winter.
• Rooms that never quite cool down on hot afternoons.
• Dust and outdoor odors coming in through gaps around attic hatches, recessed lights and rim joists.
• Heating and cooling equipment that runs longer than it should.

In Southern Utah, where summer cooling loads dominate, a leaky attic plane or garage wall hands hot air directly to your air conditioner. Insulation slows heat, but it does not stop moving air. Air sealing does that. If you are thinking about the other half of the envelope, our guide to energy-efficient windows, insulation and shade for desert homes covers it.

How a blower door test works, step by step

The test usually takes one to three hours for an average single-family house, longer if the tester is also hunting for leaks. Here is the typical sequence.

1. Prepare the house. Windows and exterior doors are closed and latched. Fireplace dampers are closed, and combustion appliances are set so they cannot backdraft. Interior doors are opened so the whole house is one pressure zone.
2. Install the frame and fan. An adjustable panel goes into an exterior doorway with the fan mounted in it.
3. Measure the baseline. The tester records the pressure difference between inside and outside with the fan off, so wind does not skew the result.
4. Pressurize or depressurize. The fan is ramped up until the house reaches 50 Pa. The tester records the airflow required, often at several pressure steps.
5. Calculate the result. Software converts the airflow into CFM50 and, using the home’s volume, into ACH50.
6. Find leaks (optional but useful). With the fan running, the tester can use a smoke pencil, an infrared camera or simply a hand to find where air is rushing in.

This is the standard procedure described by the Building America Solution Center. Homeowners do not need to do anything except make the house accessible and keep pets and kids out of the doorway.

Pressurizing versus depressurizing

Most testers depressurize: the fan pulls air out, so outside air is drawn in through every gap. This makes leaks easy to feel and trace. Pressurizing pushes air out instead. Both are accepted methods, and the choice is up to the tester and the test standard being followed.

Blower door test for new construction

If you are building a custom home, a blower door test is likely part of your project, either because your local code requires it or because you want proof that the envelope performs. Timing matters.

Final test. For new construction, testing is generally done after finish electrical, mechanical and plumbing work is completed, because the penetrations for those trades are common leak points. This is the number that goes to the building department when code requires one.

Mid-construction test. Many builders also run a test after insulation and air barrier are in place but before drywall. At that stage every leak is visible and fixing it takes a caulk gun or a can of foam, not a drywall repair. If your builder offers a pre-drywall test, say yes.

Where new homes typically leak

Air-sealing the roof and foundation areas is central to passing the first time, as Fine Homebuilding has reported, and in practice the trouble spots are consistent from house to house:

• Top plates and the attic floor, including attic hatches and pull-down stairs
• Recessed can lights and other ceiling penetrations
• Rim joists and sill plates at the foundation
• Plumbing, electrical and duct penetrations through the envelope
• Garage-to-house walls and doors
• Window and door rough openings
• Fireplaces and chimney chases

The garage deserves special attention because it is both an air-leakage path and a source of fumes. Our article on garage insulation options and sealing air leaks first walks through that.

Blower door test cost

For most single-family homes, expect a blower door test to cost between $200 and $450, with an average of about $325 according to Angi’s 2026 data. HomeAdvisor puts a standalone blower door test at $350. Both note that duplexes and multifamily buildings cost more because each unit needs its own setup.

The price moves with:

• Home size and complexity. Bigger or multi-level houses take longer to set up and seal off.
• Location. Travel time to a rural lot adds cost, which matters across the spread-out communities of Washington and Iron Counties.
• Scope. A simple pass/fail test for a permit costs less than a test with leak hunting, thermal imaging and a written report.
• Timing. Multiple visits (pre-drywall, final and a retest after a failure) add up.

When you are building, ask whether testing is in your contract price or is a separate line item. If you want to see where testing sits among other expenses, read what affects the cost of building a home.

Blower door test results explained

You will see a few numbers on the report. Here is what they mean.

ACH50 is the most common reporting format: results are frequently standardized into ACH50, which lets you compare a small house with a large one. A lower number means a tighter house.

What is a good result?

It depends on the code that applies to your project and your own goals. As one example, Illinois’ 2023 residential stretch code checklist lists 3 ACH50 for the prescriptive path and 5 ACH50 for the performance and ERI paths. That is one state’s requirement, not a national rule. Your local building department sets the threshold that applies in your jurisdiction, and your builder and energy rater should tell you the target before drywall goes up.

As a rule of thumb, lower is tighter, and a number that comfortably beats the code target leaves room for error on test day. A house that barely passes in a mid-construction test can slip over the line once finish work adds more penetrations.

What happens if you fail

Failing a required test means the house leaks more than the code allows. The fix is straightforward: locate the leaks, seal them and test again. Most failures come from a handful of fixable gaps, not from a fundamentally flawed house.

A practical sequence after a failed test:

1. Run the fan again in leak-finding mode. Walk the house with the fan on and check the common spots listed above.
2. Seal the biggest leaks first. Large openings, such as an unsealed attic hatch or open chases around plumbing, usually account for more leakage than dozens of small cracks.
3. Use the right materials. Sealant at framing joints, gaskets at doors, foam at penetrations, and gasketed covers at recessed lights. The materials need to be rated for the location, for example fire-rated products near flues.
4. Retest. Schedule the tester again. Ask in advance whether the retest fee is quoted separately.

To avoid the whole cycle, ask your builder to treat air sealing as a planned task with a target number, not as a cleanup step. Testing before drywall catches most problems when the fix costs very little.

Tight house, planned ventilation

An airtight house is only half the plan. As envelopes become tighter, mechanical ventilation becomes essential for indoor air quality. Building scientists use the phrase Build it Tight and Ventilate Right. Guidance from the Midwest Energy Efficiency Alliance notes that airtight homes require mechanical ventilation, that balanced HRV and ERV systems provide fresh air, and that ERVs also exchange moisture.

This ties directly to rooms where moisture and odors build up:

• Bathrooms need fans that are properly sized and ducted to the outdoors. See our guide to permit-ready bathroom ventilation requirements.
• Kitchens need range hood planning that works with a tight envelope. Read about kitchen ventilation options, from ducted to recirculating.

If a range hood exhausts a lot of air, a tight home needs a plan for where the replacement air comes from. Raise this with your designer early, not after the test.

Blower door testing for remodels and additions

You do not need a new build to benefit. A blower door test before a remodel gives you a baseline and a map of leaks, so the work you do (new windows, attic insulation, a finished garage) targets the right places. A second test after the work shows what the money bought.

When you are opening walls or ceilings anyway, air sealing is cheap compared with doing it later. A room addition is a good example: the new framing meets the old house at a seam that is easy to leave leaky. Likewise, converting a garage or basement into living space puts a conditioned room against an unconditioned one, and air barrier continuity matters.

A few ideas for homeowners planning ahead:

• Ask for a baseline test before you start if the home is older.
• Treat attic access, rim joists and penetrations as scope items in your estimate.
• Keep up with regular upkeep too: seasonal home maintenance tips can help you handle the small seal-and-repair jobs that otherwise creep up on you.
• For a new home, a final walk-through is also the time to confirm the test report is in your file. Our new home walkthrough checklist lists what to check before closing.

Our perspective

We think of a blower door test as a quality check on how well the design and the build agree with each other. It is not something to dread, and it is not an afterthought to schedule in the final week.

Our approach is built on a single point of contact for design and construction, so the person who talks to you about how the house will look is also tied into how it is built. That is how we aim to keep air barrier details, ventilation choices and the energy goals you gave us in the same conversation, from the first virtual consultation and 3D rendering onward.

Our advice to homeowners is simple. Decide your airtightness goal in the design phase. Plan ventilation as a system, not a patch. Ask for a test before drywall. A tight house is a comfortable one, and the cheapest leak to fix is the one you find while the framing is still exposed.

Jake

Planning an energy-efficient build or remodel with us

If you are planning a custom home, kitchen remodel, addition or ADU in Washington or Iron County, Utah, we can build air sealing and ventilation into the plan from day one. Published ranges on our pages give you a starting point: bedroom additions run $25,000 to $75,000, family room additions $40,000 to $120,000, and garage conversion ADUs $60,000 to $120,000.

Start with our custom home construction service, explore room additions or ADU builds, or get in touch through our main site to talk through your project.

FAQ

What is the average cost of a blower door test?

For a single-family home, most people pay between $200 and $450, and the average is around $325. Duplexes and multifamily buildings cost more, and extras such as thermal imaging or a full energy audit raise the total.

What is a good blower door test result?

A good result is one that meets or beats the ACH50 target your local code sets. As an example, Illinois’ 2023 stretch code lists 3 ACH50 on the prescriptive path. Ask your building department or energy rater for the number that applies to your address.

What happens if you fail the blower door test?

You locate the leaks, seal them and retest. Running the fan while someone checks the attic hatch, rim joist, light fixtures and penetrations usually reveals the biggest problems. Testing before drywall makes the fix easier.

How do they do a blower door test?

A technician mounts a calibrated fan in an exterior doorway, closes windows and exterior doors, and runs the fan until the house reaches a standard pressure, typically 50 pascals. The airflow needed to hold that pressure is converted to CFM50 and ACH50. The whole process is described by the Building America Solution Center.

Sources

• Enclosure Leakage Test, Building America Solution Center
• How Much Does a Blower Door Test Cost? Angi
• What Does a Home Energy Assessment Cost? HomeAdvisor
• Performance testing of new homes, University of Minnesota Extension
• Residential Air Sealing and Ventilation, Midwest Energy Efficiency Alliance
• Compliance Checklists for IL 2023 Residential
• Fine Homebuilding

Recommended

• Homeowners & Builders: Permit Ready Bathroom Ventilation
• 5 Garage Insulation Options for Homeowners: Seal Air Leaks First
• Kitchen Ventilation Options: Ducted, Recirculating and More