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Blower Door Testing

Watch an explanation of the blower door test during a guest appearance at the Montgomery County Energy Connection video shoot.

Blower door test in Maryland

Blower door test set up in Maryland

Blower Door Testing Maryland

Air barriers throughout a house are tested during a blower door test and it is not uncommon for many of them to fail.  The higher the measurement of the airflow the sensor in the blower door fan reads, the larger the leakage area around the house. 

Targeted air sealing with blower door testing

Additional diagnostic tests can be performed with the blower door to help isolate the worst leakage points so air sealing can be targeted and results driven.

For every cubic foot of air that leaves the house through the fan at the door during a blower door test a cubic foot of air replaces it from all of the holes and cracks in the foundation, walls, ceiling, inefficient windows and doors as well as many other places around the home that you may not be aware are connected to the outside. The leakage points that are revealed during the blower door test are passive gateways for conditioned air to leave and unconditioned air to enter every day, all month, each year, after year costing homeowners needless comfort issues and energy loss.

Once the test is running and the sensor is connected to the meter for pressure and air flow readings, it is best to walk around the home and perform a physical inspection to find air leakage places and determine the most effective treatment for the problem. It is really amazing to see where all of these leakage points occur and often times it is right in plain sight. 

A blower door test could help uncover four or five DIY solutions that will save hundreds over the course of time and could literally be the difference between a drafty house and and comfortable home.

Blower Door Demo

5 Reasons to Get a Blower Door Test in Maryland

1. No More Guessing Games

A blower door test is a great way to isolate problem areas of the home as it relates to communication with the outside.  One example would be to isolate an area of the home that is causing an issue.  If there is an upstairs bedroom that seems particularly warm in summer, a blower door test may reveal that the room is connected to the outside.  It could be through an un-caulked window molding, or a light fixure.  A blower door test can help guide us to the issue.  If the room is not connected to the outside, maybe the duct that supplies heating and cooling is disconnected or un-insulated.  A blower door test helps eliminate issues in order to find the root cause of the comfort problem.

2. Confirm Window & Door Theories

If I had a nickel for every audit I have done where the homeowner is in a debate with their spouse/partner about where the drafts are coming from.  In some cases, both are convinced that the drafts are from the windows.  An air leakage test using a blower door is the best way to prove or disprove any theory about how leaky the windows are in the house.  Using odorless smoke pens and toy smoke makers, drafts in windows and doors can easily be uncovered with the use of a blower door test.  Even the smallest of leak can be detected and determination about new windows can be made from the position of confirmed information.

3. Seeing Air Leak Into Your House is Empowering!

There are several places around your home that you will be shocked to learn are leaky and don't just take our word for it!  We will whip around your home during the blower door test and watch and feel the air stream in.  There are places in the basement, in the ceiling and in the walls.  The other side of the coin is the places where you won't find any leakage.  That is equally important and should have an impact on feeling in control!

air sealing a maryland house

4. Uncover Leakage Points that are Hiding in Plain Sight

Each and every day we go into our favorite bathroom and we spend some quality time. Those of us that are considerate flip on the exhaust fan and let it run for the duration.  Have you ever gone into that bathroom on a cold winter morning and felt a temperature difference below the fan?  Ever wonder why?  An air leakage test will expose the bath fan as an offender - a secret gateway to the attic - where cold and hot air reign supreme.

5. Compare Your House to Similar Size Houses

When you have a blower door test done with an experienced building analyst, you will receive feedback about the results of your air leakage test compared to those of similar sized houses.  Although no two houses are exactly the same, fair and reasonable comparisons can be made based on the age and style of the home compared to others in Maryland. Knowing how your house compares to your neighbor is a good way to set goals and aspire for change with examples of success to model after.

Maryland blower door contractor

Thermal imaging during the blower door test reveals a stream of cold air.

Blower Door Tests Reveal Air Leakage

A classic benefit of a blower door test is getting great results from thermal imaging while the blower door is in test mode and the leaky spots have air (hot or cold, depending on the time of year) streaming in from the outside.  In this thermal imaging pair, the standard image shows the recessed light above the shower as the point of focus to determine if there is a thermal bypass in that location.  

One way, of course, to determine if it is leaky is to put your hand up and do a physical inspection.  If the area is hard to reach, such as this light fixture, thermal imaging can reveal how much of a connection there is by the amount of cold or warm air that is detected by the camera.

Blower Door Setup in 2.5 Min

Maryland Blower Door Testing Experts

The blower door is set up at the doorway and depressurizes the house (pulls the air out) and as a result gaps, cracks, holes, penetrations and several other culprits allow air to stream in!

Contractor for Blower Door Testing

Reference photo of shower recessed light.

What to expect during a blower door test

A common question that is asked when a person sees the blower door for the first time is whether or not they need to leave the house during the test. The answer is no. 

One key to understanding how the blower door works is to take this misconception by many and show why it is not a dangerous test in any way.  Thinking about pressure a little bit in terms of hamburgers might help.

When the depressurization of the house reaches -50 pascals (a way to finely measure pressure) the result is recorded for the test.  To give some perspective, the weight of one pascal is about 1/4 lb.  So, the test has the equivalency of around 12.5 lbs. of pressure and all of the pressure is focused at the fan.  The air that is running through the house after hitting -50 pascals is coming from the outside - through the house - and back out through the fan.

To put that in perspective, if the house were air-tight and the blower door was running, the air would evacuate and there would be nothing left to breath.

While the blower door is running it is a great time to walk around and determine how connected the house is to the outside at key locations around the thermal and pressure boundary of the home (envelope).

Blower Door Testing Equipment and How it is Used

Blower door testing experts Maryland

Blower door test equipment set up and ready to depressurize this Maryland home.

The blower door test is a Model 3 110V System fan that is suspended in the front door by a frame that is designed to be portable so it can be assembled in any home.  The fan pulls air from inside of the house to the outside creating negative pressure.  During the process of making the house go negative, the sensor reads the amount of air flowing through once the pressure reaches the desired goal. 

It is good to hire a properly certified company to perform a blower door test so that the equipment is set up correctly and safely.  Incorrect configurations could lead to improper results or possible damage to the home if the test is not secured properly.

Air leakage testing Maryland

Configuration rings allow the technician to restrict air flow for accuracy.



A blower door is in fact a large, industrial strength fan, that has several components that make it much more than simply a fan.  A special sensor and several pressure input pins allow for configurations to perform a multitude of testing procedures and diagnostics.  A blower door is not an inexpensive piece of equipment and it must be calibrated per the manufacturer's specifications.  Field calibrations keep the fan running well and they are quite durable and heavy!

Residential building leakage test Maryland

A pressure and flow guage can help uncover air leakage points in a home.


The pressure and flow gauge is the hub of the blower door test and pulls the data from the pressure tubes and interprets the information into measurable results.  A manometer, the formal name for the gauge, is a tool that can also be used to discover areas of the home that may be more connected to the outside than other areas of the home.  Other interesting tests can be performed such as the hole to zone test where a pressure gauge can actually provide information with the blower door running to determine fairly accurate data about how large the hole is to the zone expressed cumulatively.  In other words, it provides an easy to understand measurement in square inches how large the hole is to the outside zone (an attic for example) without having to measure every single tine crack and crevice.

Here are the Best Ways to Do Very Well on a Blower Door Test


When it comes to sealing up a pre-existing home (retrofit) it is important to note that not every measure on this list is ideal based on a cost vs. value analysis, however it is important to note that when building a new home, building an addition or simply doing remodeling around the home it is super important to be familiar with each of these items because they are all great opportunities to decrease energy use and increase comfort.  

1. Air barrier and thermal barrier. 

  • A continuous air barrier/pressure boundary must be installed in the building envelope.
  • Exterior thermal envelope contains a continuous air barrier.
  • Breaks or seams/joints in the air barrier must be sealed.
  • Air-permeable insulation (fiberglass batts) should not be used as sealing material.

2. Ceiling/attic

  • The air barrier/pressure boundary in any dropped ceiling/bulkhead/soffit should be aligned
  • with the insulation and any gaps need to be sealed.
  • Access opening, drop down stairs or knee wall doors to unconditioned space should be sealed.

Classic thermal/pressure boundary issue  

The attic hatch is a classic pressure and thermal bypass which requires treatment.

3. Walls

  • Corners and headers should be insulated and the junction of the foundation and sill plate must be sealed.
  • The junction at the top plate and top of exterior walls should be sealed.
  • Wall insulation should be in continuous alignment/contact with the air barrier
  • Kneewalls should be sealed.

4. Windows, skylight and doors

  • The space between window and door jambs and framing as well as skylights and framing should be properly sealed.

5. Rim Joists

  • Rim joists should be air sealed (air barrier) and insulated.
  • Floors (above garage/cantilever)

6. Insulation must be installed and affixed to the underside of the subfloor plywood.

  • The air barrier must be installed at any exposed edge of the insulation.

7. Crawl Space Walls

  • Encapsulation is recommended including installing vapor barrier at the floor, sealing and insulating the walls and disconnecting the space from the outside.

8. Shafts, penetrations

  • Utility penetrations,
  • Shafts for ducts
  • Conduits for wiring
  • Flue chases that open to the outside or unconditioned space should be sealed.

9. Narrow Cavities

  • The proper insulation solution should be used to block and seal any irregular voids.

10. Garage Separation

  • Air sealing should be done between the garage and conditioned spaces.

11. Recessed Lighting

  • Recessed light fixtures installed in the thermal/pressure boundary should be air tight, IC rated and sealed to the drywall.

12. Plumbing and wiring

  • Batt insulation should be cut neatly to conform to any wiring and plumbing located in exterior walls.

13. Shower/tub on exterior wall

  • Outside walls connected to showers and tubs shall be insulated and the air barrier installed separating them from the shower and tub.

14. Electrical/phone box on exterior walls

  • The air barrier must be installed behind electrical and communication panels/boxes or air sealed boxes should be installed.

15. HVAC duct measures

  • HVAC register boots that go through the thermal boundary shall be sealed to the sub floor or drywall to eliminate leakage/waste.
  • All ducts outside of the envelope shall be sealed and insulated to a minimum of R8.
  • All ducts inside the envelope shall be sealed at the seams and any other cracks/crevices with Mastic.

16. Fireplace

  • An air barrier should be installed on fireplace walls and the doors on a fireplace should be gasketed.

Blower Door Testing in Maryland

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Eric Gans
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Helping You!

*Improve home comfort
Educate you about your home
*Find air leakage in your home
*Improve energy efficiency
*Use science for solutions
*Assess your building's shell
*Help prioritize improvements
*Find the root causes
*Assess insulation levels
*Measure indoor air quality
*Evaluate windows & doors
*Evaluate attic ventilation

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    Our mission is to help Maryland homeowners create a more comfortable home and save energy. We achieve this by applying building science principles and modern air sealing and insulating techniques.

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