Source Control Comes First for Good IAQ
There’s no mystery about how to achieve good indoor air quality (IAQ). But there’s a lot of misinformation and misunderstanding. If you listen to know-nothing influencers, you might think all you need to do is buy whichever magic device they’re promoting. But no one thing by itself can get good IAQ for you. You need a comprehensive approach. And it starts with source control.
The allure of the magic pill
We live in the age of the Internet and social media. With the huge potential for education they hold, we could be living in a golden age. Alas, they also allow misinformation to spread as quickly—or more quickly—as the stuff we know to be true.
I don’t need to say much here because I’ve already covered why you should avoid most electronic air cleaners. The claims made their promoters often are not backed up by real data. In fact, a new study on the interestingly named bipolar ionization method found that they result in “limited pathogen reduction.”
So, using these “magic devices” has been described by some experts as doing uncontrolled chemistry experiments with your indoor air. Yes, they may get rid of some of the bad stuff in your indoor air. But they also may create new pollutants.
A comprehensive approach to IAQ
One of the most important maxims of building science is that we look at everything with a systems approach. A house is a system. An air barrier is a system. And achieving good IAQ also requires treating it as a system.
There are many ways to look at improving indoor air quality. In the twenty-plus years I’ve been in the field of building science, I’ve refined my understanding of IAQ a lot. I now promote a 7-step approach to achieving good IAQ:
- Source control
- Airtightness
- Filtration
- Ventilation
- Moisture control
- Pressure balancing
- IAQ monitoring
Go read my article for more detail on the 7 steps. Better yet, sign up for my online course on the 7 steps to good IAQ. Here’s a little glimpse of what you’ll learn:
Why source control is first
It’s obvious, though, isn’t it? Let’s say you’re in line to get into a popular club. Near you is someone who’s loud and rowdy and obviously drunk. If the guy controlling the door lets him in, it’s going to be harder to remove him when he acts up inside the club. So they just don’t let him in.
It’s the same with source control for good IAQ. Keeping the pollutants out from the start makes it easier to keep the indoor air clean. You may not need as much ventilation. Filters don’t need replacing as often. The IAQ monitors show good results.
![Max von Pettenkofer source control quote as paraphrased by Ole Fanger (probably) [image from Fanger's 2006 paper, What Is IAQ?]](https://www.energyvanguard.com/wp-content/uploads/2026/01/pettenkofer-quote-ole-fanger-paper-2006.png)
And we’ve known this for a long time. The message in that quote above (more on that below) is from 1858. A German chemist and hygienist named Max von Pettenkofer made the point clearly that source control is the starting point. Why would you just turn up the ventilation if there’s a dung heap sitting on the living room floor?
About that source control quote
Now, let’s talk about that quote. I like to find out the source of quotes because in these days of Internet and social media nonsense, you just never know. Abe Lincoln said it best:
I couldn’t find any original source for that Pettenkofer quote. (Quote Investigator works for more popular quotes.) The furthest back I could find references to was about 20 years. Since then, it’s been used by a bunch of us in the IAQ community. I first saw it in Joseph Lstiburek’s article, First Deal with the Manure and Then Don’t Suck. And he actually pointed to what is probably the original source of this version of the quote in a footnote in that article.
A few days ago, though, I was thinking about this quote again and asked my friend Steffen Petersen about it. He’s a professor of building science in Denmark and does a lot of work in the field of IAQ. He turned out to be the perfect person to ask. He sent me several Pettenkofer quotes in the original German and also translated. Here’s the one that most likely morphed into the current version:
Ein Raum, welcher einen verwesenden Misthaufen einschliesst , wird trotz aller Ventilation eine ekelhafte Wohnstätte, ein Herd für schlechte Luft bleiben. Erst wo die Reinlichkeit durch rasche Entfernung oder sorgfaltigen Verschluss luftverderbender Stoffe nichts mehr zu leisten vermag, beginnt das Feld für die Ventilation.
That translates to:
A room that encloses a rotting dung heap will, despite all ventilation, remain a disgusting dwelling place, a breeding ground for bad air. Only when cleanliness, through the rapid removal or careful sealing of air-polluting substances, can no longer achieve anything, does the field for ventilation begin.
Yeah, that’s basically the same thing. As far as Dr. Petersen can tell, the current version originated in the 2006 paper by Ole Fanger titled What Is IAQ? The image with the quote in the previous section is from that paper. Dr. Fanger was also a Danish researcher who did a lot of groundbreaking work in the field of thermal comfort and indoor air quality. And he had a most interesting hair style, as you can see above.
Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and is the author of a bestselling book on building science. He also writes the Energy Vanguard Blog. For more updates, you can follow Allison on LinkedIn and subscribe to Energy Vanguard’s weekly newsletter and YouTube channel.
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Conservation of mass assures us that the pollutants have to go somewhere. If you move them outside, they may be diluted but will still eventually find their way back in through ventilation or infiltration. If the pollutants are known, shouldn’t they be put through a chemical reaction that could end the pollutant status?
Continuing the dung analogy, and borrowing from permaculture systems approach (‘A problem is a solution that hasn’t been discovered.’), if the dung was removed and buried around trees, it could feed their growth, thereby assisting in the reduction of particulate pollution and increasing oxygen output and CO2 absorption, improving overall air quality.
Steven: Good point. Then there’s the quote by Eric Sevareid: “The chief cause of problems is solutions.”
Stacy: Moving pollutants from indoors to outdoors is only one way doing source control. The primary one, I’d say, is paying attention to what you bring into the house to begin with. Also, radon is a noble gas and reacts with almost nothing. Even if it did, the danger derives from its radioactivity, which doesn’t change even if it is in a compound.
Allison, https://www.digitale-sammlungen.de/de/view/bsb10767804?page=83
This is from Pettenkoffer’s publication from 1858 “Über den Luftwechsel in Wohngebäuden”, loosely translated as “About air exchange in residential buildings”, see sentence in the middle of the page starting with “Ein Raum…”
That’s the original, here is also a digitized copy:
https://archive.org/stream/bub_gb_3aFLAAAAcAAJ/bub_gb_3aFLAAAAcAAJ_djvu.txt
Search for “Misthaufen” (english: pile of manure). It only comes up once in the entire text and that’s the paragraph later paraphrased by Fanger.
Paul: Thanks for the link. I should have mentioned the title of the book it came from, so thanks for adding that, too.
Interestingly enough, the first part/chapter of his publication is titled “About a method for determining the carbon dioxide in the atmospheric air”:
https://www.digitale-sammlungen.de/de/view/bsb10767804?page=7
Many years ago, when I followed the old IAQ discussion group, I learned that one huge source of contaminants is often the leaking portable vacuum cleaner. Newer ones have gotten lighter and leakier. Switching to a central vacuum system, and using for all dusting and floor cleaning, was often a great (but overlooked) way, to reduce pollen, dust, and mold spores.
Richard: Yeah, vacuum cleaners can put a lot of particles into the air. But they don’t have to. Some come with HEPA filters. And central vacuum systems may create another problem. If they’re outside the building enclosure, they can depressurize the house, increasing infiltration.
Allison: Do you really think a central vacuum runs enough to affect overall infiltration in a house? I like the trend of getting rid of carpet and using Swiffers instead. Unfortunately, many have gone the Roomba route. I doubt that those devices have much of a filter and probably run and stir up dust a lot longer than conventional vacuums. This would be a good area for future research.
The idea was that portable vacuums leak so much they are often the largest source of dust. Switching to central vacuum takes care of that.
Richard, but as Allison points out, a central vacuum sucks, I mean it potentially contributes to infiltration through unknown paths in the enclosure, and therefore sucking in potential contaminants: insulation dust, other dust from interstitial spaces, mold spores from crawl spaces, pollen from outdoors when we don’t want them. For an hour a week, or so.
Portable vacuum cleaners leak, more or less, but they also stir up quite a bit of stuff off the floor with their exhaust ports. We are doomed.
I can highly recommend Dr. Bailes’ course on the 7 steps to good IAQ. Besides being excellent information, well-presented, it was also 8 rather inexpensive Whole House BPI CEUs. 🙂
And Dr. Bailes, your book A House Needs to Breathe, or Does it?, is THE book I wish I’d had fourteen years ago when I started my energy auditing business. It’s the best thing I’ve read on Home Performance.
Teresa: Thanks! I appreciate the testimonial. For anyone who wants to buy the book, we have it in paperback and digital formats in our online store.
https://energyvanguardstore.com/
Thanks for all you do – I really enjoy your work. I offer a variation for consideration. If you move moisture control to the top, you are “controlling the source” by minimizing potential for bioaerosol growth in the first place. “Dry houses don’t grow stuff” is an axiom that I think has some validity, subject to the usual “but what about…” .
Bruce: Good point. I didn’t mention it in the article, but airtightness and moisture control both can be considered a type of source control as well. I’d still put source control at the top, though, because it controls more than microbial growth from moisture problems.
You’re obviously pulling our leg on the Abraham Lincoln ‘quote’ about the internet.😊 I’m surprised no one commented on that.
Oh, would I do that, Marvin? ;~)
Unfortunately, we will probably continue to occupy our minds with challenging IAQ questions for a time to come because of our insistence to introduce air pollutants into the built environment. Carpets, adhesives, paints, resins in engineered wood, insulation and furniture, even interior bug screens.
I recently discovered that the bug screens in our home still stink. These are interior screens because the windows are casement type opening to outside. PVC or whatever else is in those fiberglass screens (plasticizers?) stinks, even after a few years of off-gassing.
First, I am going to do source reduction by removing all screens from windows we rarely open. Second, I will look for a non off-gassing bug screen. Wish me luck with the second task.
Consider stainless steel or aluminum screening.
Thank you, JC, for stating the obvious. Haven’t used metal screens in quite a while (at least as window screens) and they left my brain repository of materials. Note to self: stop relying on my brain so much.