Blower Door Testing. Please proof this new inspection article.

Blower Door Testing.

Preparation must also include inspecting for the presence of asbestos anywhere in the building envelope that could be disturbed. Also, instead of removing ashes from the fireplace or wood stove one can also cover them with wet newspaper since any remaining dust is likely to become airborne.


Is there any need to comment on the fact that things can be drawn into the
building enveloped such as mold, asbestos, allergens, attic dust/insulation,
pollutants, etc… ? Is the inspector liable for any of these issues? To say
these things can NEVER be drawn into the house is naive IMHO.


A few items I would address in your article:

-50pa is a standard for BPI or HERS (Resnet) testing procedures. 75pa is the standard for large building (commercial and industrial) testing via ASHRAE, ASTM, USACE and AABA.
-CFM is usually only the starting point for calculations. ACH, EqLA (US and LEED), EfLA (Canadian) and a host of other numbers are usually the end result, not CFM. This also depends highly on the weatherization program as to what number is used at the end of the day. CFM @ air flow (pa is not the only one used, just the most common) is just straight air flow, where many of the other numbers take in consideration the volume or square footage of the structure.
-USACE standard is .25CFM/sq ft at .3in of water gage (75pa). 1500 CFM is a generic number that is often used for a threshold of leakage.
-ASTM (E 2178 ) standard is an air barrier not to exceed .004 CFM/sq ft at .3 in wg (75pa)
-ASTM E-779 is the actual testing procedure that is followed. It calls for an average leakage rate of no more than .25cfm/sq ft at 75pa through depressurization and pressurization. Then divide the average measured air leakage flow rate in both directions by the surface area of the enclosed envelope by the continuous air barrier of the building.
-As a side note to ASTM E-779, there was already an ASTM standard in place for use of thermography before the Resnet standard. That test has to be done in accordance with ISO 6781:1983 and ASTM C1060-90 (1997) and finally ASTM E 1186-03 is the procedure standard for air leakage site detection.
-blower doors have other uses in the clean room integrity testing and fire suppression markets. Those applications have their own set of standards and procedures.
-longer term base lines in conjunction with a longer term testing procedure can also baseline out wind (to a certain point) and other factors…including stack effect.
-In addition to air density and viscosity, items within the structure are resistant to flow and take up volume within the structure (volume is used for ACH and other related numbers). This calculation can be accomplished via the N factor calculation. Some systems have this ability built right in to the unit while others have to use external software for this calculation.
-structures with swamp coolers have to have the supply and/or returns sealed off.
-As James stated, one of the biggest safety concerns is asbestos. Those structures can only be pressurized and even then it really should be abated first.

Jason Kaylor – JJ
VP of Specialty Products
AC Tool Supply
Home Energy Audits
Blower Door
Cellulose Insulation Machine
Tramex Moisture Encounter Plus

This is a huge point that should be addressed within the article!


The blower door simply simulates (@50 pa) what a 20 mph wind does at one side of the side of a house. It is not creating a condition that is unknown to that environment.

What you would not know, since it cannot be seen or measured by an IR device, is the fact that the pollutants that you are referring to are continuously flowing in and out through air leaks that only a blower door can measure.

The tester does not want to dirty carpets or have draperies knock delicate things from shelves and window sills under his watch, so he will take care to ensure that the condition of the home is as he found it when he leaves. Thus, he will take care to protect these items.

That is a valid point James, but the door amplifies these effects in a big way. A BD has “better access” to interior side leaks, that wind may have little to no effect on, as far as stirring up pollutants goes. Your fireplace ash example is a good one. If you leave ashes in your fireplace the wind may blow a few in to your house. Where a blower door throws them everywhere.


I have talked to many inspectors who will no longer perform
blower door testing because they have seen first hand the
health affects it had on their clients and even themselves.
This debate is going on behind the scenes by a lot of people.

I am with John on this one, I am not as experienced as he is, however my limited exposure to blower doors is similar. I am not sold on the benefits being greater than the risk.

yeah but that is highly over exaggerated by people. There were many studies done in the 90’s and early 2000’s on blower door usage and IAQ issues. The bottom line is the pollutants are there anyway and they need to be dealt with one way or another. If the ASTM procedures are followed, then it is basically a moot point.

The real problem in the industry I see is that people think they can just pick up a blower door, a BPI or Resnet certification and then out and get to work. A strong background or re-education in building science is a must.


I’m sure that the guys claiming to do “energy audits” with nothing but IR cameras will oppose the use of a blower door to anyone who will listen. I just don’t happen to be one.

Depressurization within the home is a naturally occurring phenomenon and the use of a blower door to measure air leakage and stop it is safe and effective. To continue to use your clothes dryer and/or air handler to suck in pollutants does nothing to help anything. Neither does taking an IR image of 10% of the 300 different points that need to be sealed.

But the most important use of the blower door comes into use AFTER the leaks are sealed and the need to determine the sufficiency of the remaining ACH to safely operate combustible devices comes into play.

I agree with this statement, but to add another point, it also assists in keeping the frauds (contractors & pretend EA’s with no BD’s) at a minimum (before & after tests for work completion verification), those selling and installing windows come to mind… I like IR cameras, but they are only one part of your diagnostic tool chest as an EA…

After many blower door tests… probably close to 100, I have never had a problem with the above and I’ve worked in some pretty crappy places!!

I usually find these statements are made by people who have not experienced blower door testing and are just assuming.

I have heard it from people that used blower doors for many years.
It is naive to say it never happens and is not a consideration. Did
you do lab test to verify your opinion?

It is common knowledge that leakage in return ducts in the basement
and crawl spaces can introduce indoor pollutants into the rest of the
home, such as dust, radon and mold spores, etc…

Why would a blower door not be capable, in some cases, of introducing
pollutants into the home?

John, first of all I never said it doesn’t happen, just I have never seen it, nor have I heard of anybody in my area that has a problem with it and I belong to a couple of state wide performance organizations. Granted this subject does get brought up in training classes but it is not the problem you make it out to be.

Furthermore, anyone who gets into this business should have the proper training and related experience so if you do run into a situation like you described and you observe a condition that might be hazardous obviously you don’t do the test.

I am talking about issues being created AFTER the test, not before.

John, a blower door doesn’t “create” spores, radon, etc out of thin air. The problems were already there. They have to addressed before performing the test.


If the blower door draws into the house pollutants that were
not part of the indoor environment, then the blower door
created the problem.

You can have a lot of things outside, in the attic, under the house,
and inside the walls that are not an issue until you draw them
into the indoor dwelling.

You have said stupider things…much dumber things…than this. But this one is very close to the top, Bubba.

Back in the day…when you were inspecting homes…did you report to people that the home had mold in the attic, in the walls, and under the house when you saw it there…but that this was “no issue”? Did you and the real estate salesman conspire to simply omit it from the report or did you find some softer words to describe this “non-issue”.

The certification class you wrote a few months after you bought your first camera…do you teach people that moisture detected in the attic, wall or under the house (since it is outside of the “indoor dwelling”) is a “not an issue”, too? I thought you photographed it and patted yourself on the back for saving them some money? But if mold grows from that moisture and collects within the walls, attic and below the house…that’s “not an issue”, eh?

When air escapes through a leaking area, Bubba, the same amount of air that leaks out is also drawn in - replaced - through leaking areas…from the moldy attic, the moldy inner walls, and the moldy area beneath the house. This is what makes people sick, Bubba. Blower doors do not create conditions that do not already exist when the wind blows against the side of the house.

What you say is “not an issue” can actually make people sick from normal air exchange. The blower door simply measures that exchange…before and after retrofitting…by simulating a 20 mph outdoor wind (depressurization @ 50 pa).

People pay you for this advice?

I know very little about blower doors, so this is why I am asking this question:

Why is negative pressure used more then postive pressure with a blower door?