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Building Science

5 Reasons to Own a Blower Door

A means for diversifying your skill set, toolbox, and income stream

Image credit: U.S. Environmental Protection Agency

By now most of us know what a blower door does and the basics of how it works. All energy auditors and raters own one, and a few insulating contractors I know have purchased their own. As a contractor, does it make sense to invest upwards of $3500 and to take the time to learn how to operate this piece of equipment? I know of only a few contractors who have made the investment. Is it right for you? It might be. Off the top of my head, I can think of five reasons to own one.

1. It’s an essential tool for finding air leaks in a structure, and it’s a code-required test in many areas. The 2012 IRC included the first code requirement in the U.S. to test all newly built homes to verify the air tightness level. The only way to do that is with a blower-door test. Recent codes include the language: “Where required by the building official, testing shall be conducted by an approved third party.” You may not be able to conduct your own blower-door testing for code compliance, but you can definitely test the home before the third party arrives. The blower-door testing I do for code compliance includes additional charges, if the house doesn’t pass. So, searching for air leaks and fixing any problem areas before the test for compliance is conducted saves money. 

Infrared camera
To reveal air leaks, combine pressure testing with thermal imaging or smoke tracing. This is a good practice for both new construction and remodeling projects.

2. It provides an additional—and less demanding—revenue stream for your business. I bought my blower door back in 2009 to supplement my contracting business during a downturn in the economy. I trained to be an energy auditor, and that side of my business has seen steady growth over the past 10 years. Testing homes and conducting energy audits isn’t as physically or mentally demanding as working as a builder. I can see myself supplementing my retirement by continuing to perform this type of work into my 60s and 70s.

The manometer compares the fan pressure to the pressure inside the house and converts the pressure difference to a rate of airflow.

3. It’s a multi-purpose tool. Blower doors come with several different components: a frame and shroud that fit tightly in a doorway; a fan and fan speed control unit used to move air; and the “brains” of the blower door—the pressure gauge or monometer. I own a couple diagnostic tools that require a monometer, a pressure pan, and an exhaust fan flow meter. For example, a duct-blaster test requires a monometer, and a Combustion Appliance Zone (CAZ) test for the backdrafting of appliances requires a monometer. Plus, a monometer indicates if a room is being pressurized or depressurized by the forced air from heating and cooling equipment. It’s useful tool, given today’s “trust but verify” work ethic. 

4. There’s no waiting for a test. Because I’ve owned my own blower door for a long time, I tend to forget about the complexities of scheduling a test. Travis Brungardt, builder and partner at Catalyst Construction in Kansas City, MO, speaks to this issue, saying, “Scheduling an energy auditor for some point down the road costs us time. With the blower door (in concert with other tools), we can run the test whenever we need to in order to locate any problems. Then, we can run it again immediately after our attempt to resolve any issues to know if we were successful. The volatility of construction schedules makes planning these moments in advance difficult, so while we could hire a baseline blower-door test before we start and another one after we are done to confirm our efficacy, that would eliminate a lot of opportunities for us to do the most good. Owning our own blower door enables performance improvement as a byproduct of convenience. That knowledge is worth the investment.”

5. It’s an educational tool. Using a blower is an opportunity to learn where structures usually leak air. Foundation-to-framing connections, where the walls meets the ceiling, around windows and doors, and through penetrations in assemblies are all traditional leak points. Seeing those leaks first-hand often results in contractors making changes to their building techniques, which tends to produce better buildings. When you become experienced in using a blower door, you will have a better understanding of what the test results are telling you. 

I asked Jake Bruton of Aarow Building in Columbia, MO, why he wanted his own blower door. He replied, “When I bought my first door in 2014, it was because I didn’t understand what the numbers meant. I figured the best way to understand it was to have one on hand. Nobody in my market owned a door back then; I believe I was the first. Since then, the main reason I own one is because I want to verify performance prior to an expensive rater coming to test. If I can run the door the day before they are scheduled, I can find any issues and resolve them. I also have the ability to play around and find solutions that I wouldn’t otherwise find. When the HERS rater is on-site to run a blower-door test, we want them in and out ASAP to keep costs low. When it is us, we can run the entire day and explore different ideas.” 

Blower door fan
The blower door fan is used to blow air into or out of the building, creating either a positive or negative pressure differential between inside and outside. This pressure difference forces air through all holes and penetrations in the building enclosure.

The tool does require a significant financial investment—mine is the most expensive tool I own, after my truck. And it takes time and training to understand how to operate it and interpret the information it provides. But in my experience, a blower door pays for itself in the end.


-Randy Williams is a builder and energy rater based in Grand Rapids, Minnesota. Photos courtesy of the author, except where noted.


  1. d_buzz | | #1

    So, among the 2 leading products, what are the pros and cons of each, especially in their current models? Each seems to have their fans. I'd like to hear why.

    1. Randy_Williams | | #3

      Hi David, I have not had the chance to operate a Retrotec Blower Door but have heard good things about them. I don't think you could go wrong with either manufacturer. Being from Minnesota, I'm kind of partial to Minneapolis Blower Door. Convenient for me being so close to where they are built. One feature with Retrotec that I'm interested in is how they have their hose that monitors outside reference pressure sewn into the shroud. No more crawl of shame when you forget to stretch the outside reference hose on the Minneapolis Blower Door.

    2. charlie_sullivan | | #10

      I've used both, and have no complaints about either. A new Retrotec, and an old Minneapolis, and, no surprise, the new Retrotec is nicer. But that doesn't mean much, as the new Minneapolis ones look like they have similar improvements.

      1. Randy_Williams | | #11

        Thanks Charlie. I'm still using the DG-700 (2009 model) from TEC, at some point I need to upgrade to the DG-1000.

  2. jj1 | | #2

    Hi Randy: FYI Gary Reysa of designed and built a DIY homemade blower door device for less than $50, see
    Of course a DIY device is not suitable for certification work, but perhaps it could be useful for a home owner seeking to identify and seal up air leaks in an existing house?

    1. Randy_Williams | | #4

      Hi Jan, I have heard of a few people building their own blower doors to find and seal air leaks. I think that's a great idea for both homeowners and some builders. Peter Yost mentioned his first blower door was homemade using a Minneapolis Blower Door's DG-700. He couldn't achieve 50 Pa, but he could find air leaks with it. Those who are interested, the latest Unbuild It Podcast is all about blower doors, Peter mentions his homemade blower door on the podcast.

      1. user-723121 | | #7

        Hi Randy,

        When you test buildings do you always test at 50 Pascals? What about testing at 25 as well? Is leakage linear, does testing at 25 have half the CFM50 as testing at 50? Would testing at a lower depressurization replicate more closely the actual leakage dynamics of a building? I am thinking of high and low leaks being the priority for retrofit to get the best mileage for weatherization dollars. Can somehow the stack effect be replicated using a blower door?

        1. Randy_Williams | | #8

          Hi Doug,

          I use a couple multi-point test installed in the Tectite software from The Energy Conservatory, which is the software I use to control my blower door. The first is RESNET's multi-point which I believe meets the RESNET/ICC 380 standard. The test starts by taking a baseline measurements and then starts testing at 60Pa and finishes at 15Pa. The test finishes with a final baseline. Eight separate measurements are taken at 60 Pa, 54Pa, 48Pa, 42 Pa, 36 Pa, 30Pa, 24Pa, and 18 Pa. The software then estimates the size of the leakage area at 4 Pa. Your right, the lower pressures will more accurately estimate the actual leakage, thought the location of the leaks are the key and the software has no idea where they are.

          I used to use the CGSB or Canadian General Standards Board test which is also a multi-point test, very similar test starting at 50 Pa and decreasing to 15 Pa. The 2018 IRC doesn't list the CGSB as one of the approved testing methods so I recently changed when Minnesota adopted the 2018 code.

          I'm thinking about shooting some video of the different testing standards showing how the tests are performed. Would you be interested in an article showing the different test standards? I only use software to control my blower door, I feel I'm getting accurate and repeatable test results.

          Your last question, "Can the stack effect be replicated using a blower door?" Not that I'm aware of. The pressure during the blower door test is usually effecting the entire house, but you may be able to detect how bad the leakage is either high or low in the assembly if you can isolate the spaces. A zonal pressure test will indicate how much connection to the outside the space has. Again, you need to be able to isolate the area being tested. I have an article from a couple months ago detailing zonal pressure testing.

          Thanks for the question!

          1. user-723121 | | #9

            I woke up this morning thinking my question to you was poorly worded and in the time my computer was warming up you had replied. Fortunately you read between the lines and gave a very detailed answer. So much to learn about building performance, I do like the idea of (equivalent leakage area) in square inches as you showed with your hole saw demonstration. To relate the leakage area for a building in a square inch equivalent is understandable. For tighter buildings this area is quite small and shows the need for attention to detail when air sealing. Thank you for the answer.

  3. Jon_R | | #5

    While pressure is easy, I'm curious about how one might get a somewhat close CFM curve for a DIY blower door.

    1. Randy_Williams | | #6

      Hi Jon, you might be able to use a flow gauge or anemometer to measure the CFM, though a good one will set you back several hundred dollars. I believe my DG-700 mathmatically calculates the CFM using the pressure across the fan and me telling the DG-700 which ring is in use. Probably not going to use that method cheaply.

  4. user-1089563 | | #12

    Having a blower door around can also help when you want to keep dust (e.g. from finishing walls) during a house renovation from the occupied space. It is pretty simple to set up a pressure boundary with poly and a blower door. You could also do that with box fans exhausting out open windows but the blower door makes the operation so easy.

    1. user-6998645 | | #14

      Hi Don, I would just be careful to avoid running any "dusty" air through the blower door fan as things like drywall dust can get into the bearings and sensing ports resulting in expensive repairs and calibration problems.
      Back in my contracting days, I installed a large used furnace fan onto a sheet of OSB and stuck it into a doorway so as to depressurize the house when it was in the pre-drywall phase. I was always very impressed by what I found for air leaks that I could see, feel, hear or detect with smoke or incense sticks, and even a large ostrich plume feather. I got a lot of snide remarks about my feather from my colleagues even to this day.

  5. Dennis_the_Menace | | #13

    Isn't the spelling "manometer" and not "monometer" ??

  6. Deleted | | #15


  7. JenniferDehner | | #16

    I've never used a Retrotec Blower Door, but I've heard nothing but positive things about them. I'm thinking of getting one for myself, but I don't have the funds yet. I'm thinking of using to get the necessary funds. You can't go wrong with any manufacturer, in my opinion. Because I'm from Minnesota, I have a soft spot for Minneapolis Blower Door. Because I'm so near to where they're being built, it's convenient for me. Retrotec's hose that monitors outside reference pressure is sewed into the shroud, which is a feature I'm interested in. When you neglect to stretch the outside reference hose on the Minneapolis Blower Door, you won't have to crawl in shame.

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