Wednesday, December 4, 2013

Delta Q Duct Testing

At ACI California I had the chance to introduce myself to Ian Walker of Lawrence Berkeley Laboratory. I mentioned I used Delta Q Duct testing on some homes and thanked him for his work. He said that RESNET was considering it as an accepted protocol for duct testing in the future. I have used it on projects that are not HERS or any program related. I like it as it differentiates supply and return leakage which is handy for repairs.

The Beginning

LBL developed the test back in 2001 I believe and here is the link to the paper published directly below

The Formula

So for those of you that are not familiar must be asking what is a Delta Q duct test? It is a test where you perform a multi point blower door test (10 points) scaling pressure down as you go at positive and negative pressures with the air handler off and on for a total of four tests or forty points. This information is then plugged into a excel spreadsheet an viola you have the data and a cool little report. It is buried in an obscure little corner of the LBL website archived and no longer maintained. Link below

At the top of the page there are some links to Delta Q. The page itself is also not a bad little bit of information on its own for those that know little of duct testing and repairs.

The Test

I was once told that Delta Q duct testing was kind of like the dark arts of duct testing. Necromancy if you will. It is really not but I think it is a great tool especially for homes with wall cavity returns. First off there is no tape to worry about. One simply sets up a Blower Door test. If you have software great if not no problem. One must take points from 50 to 5 If you download the spreadsheet you will see this. I start off with negative air handler off. I take my ten points and enter them in the spreadsheet. Negative 10 point BD test air handler on enter data, Positive BD 10 point test air handler off enter data, Positive BD 10 point test air handler on enter data.

You need solver on your excel spreadsheet and enable macros and hit solve. You now have a test and report. It shows return leakage, supply leakage, pressure differences and ELA. Not too shabby no blue tape no clean up and your done and you have both your BD and DB numbers.

How does it work?

For me it works like this Caveman performs BD tests like told, Caveman enters data like told, Caveman hits solve like told, Caveman have report and is happy. I referenced Necromancy above did I not did I also mention the PFM factor? Now for a math challenged individual that I am I will try to explain in simple terms that I have gleaned out of the papers. It is based on the fluid dynamic of pressure difference within the different points and conditions ie negative and positive handler on and off.  The dynamics are affected system use changing by the pressures of the handler being on. These are recorded and compared by the formulas plugged into the spreadsheet.  I am sure took allot of time to develop and my description is a bit primitive. There is a bunch of math which is not fuzzy to Ian, David, Max and Paul and many others but is to me.


Chances are you are going to have to change you range. In fact with the study linked below it suggests that for accuracy you must change your range. With a very leaky house it might behoove you to find out if you can test at 50pa or 5pa before you start as this can be annoying if you run tests and then cannot reach platforms. In other words don't assume it is going to work and don't leave your duct tester and blue tape at home.  The spreadsheet allows you to manipulate pressure numbers and plug them in but I am not sure this provides the needed information for a true test. Further if I can which step up or step down figures are acceptable. It does not like windy days

Is it Faster?

My experience has been yes, maybe and no. Some jobs it goes smooth and quick others not so much. The main issues is being at the end of the fourth multi point test and not being able to maintain a steady pressure in a leaky home. This can cause a total redo. Leaky homes are a challenge and especially so on windy days. This is true with all BD test so no surprise there but the need to ramp with accuracy can be a problem that is exasperated by 4 multipoint tests. The searching for a steady point to enter can be elusive in some conditions and or points. Because of this the speed of the test can vary.


I really like the test for retrofitting, fixing and analyzing very leaky duct systems. I think we have all had that test where we could not touch 25pa. This tool is excellent because it can help identify whether or not you should be looking for a supply disconnect or attend to a really crappy return or even both. Like all of our tests it is not an end game it is just one more tool that performs better than others under some conditions we see in the field. I personally would not use it for new system verification.

Glen Gallo

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