There’s a moment in every building’s life when the air stops flowing like it should. The people inside might not notice right away, but the numbers on the energy bill start creeping up, and someone, somewhere, starts to wonder: Where’s all that air going?
For Mike Kelly, a veteran of the testing and balancing world, the answer is rarely mysterious: just overlooked. “Success is neither magical nor mysterious,” he told an audience of engineers and contractors during a recent Associated Air Balance Council (AABC) webinar. “Success is the natural consequence of consistently applying basic fundamentals. We don’t need to run into the forest. You’ve got to look at the trees sometimes and say, all right, what are we doing here? What’s the basics?”
Kelly’s stories have the ring of repeated experience, and the gentle impatience of someone who’s seen every avoidable mistake—twice. Sometimes, it isn’t a leaky seam or a faulty sealant at fault. Sometimes, it’s a sheet metal worker, early in the morning, bolting together a duct run, who forgets to peel the blue plastic off a protective wrap.
“We’re only getting airflow down half the system. Why don’t we have airflow here?” Kelly recalled. “And you have to cut a hole in the duct and find out, ‘Oh, we didn’t cut the plastic out, whoops,’ or the metal plate, or whatever it may be. It’s a little harder to leave a metal plate in, but I’m sure that’s probably a war story that’s out there.”
He prefers metal plates, always sealed with a gasket. “The protective duct wrap is a possibility. I’m sure I’ve seen it here recently, but I prefer metal.”
Percent or Class: Where the Air Goes
The core debate in specifying duct leakage, Kelly says, is: how tight do you make the system? The Sheet Metal and Air Conditioning Contractors’ National Association (SMACNA) sets standards based on duct surface area and pressure class. The AABC, which Kelly champions, pushes for percent-of-airflow considerations in design.
“In my building or my facility, I would just say we were going to be better. We’re going to make it better than that requirement. We’re going to be 1%,” he said, noting he is an advocate for specifying that a duct system can lose no more than 1% of its total designed airflow to leakage—an especially strict benchmark compared to industry standards. For context, some cleanroom or specialized manufacturing environments may require duct leakage rates well below 1%, sometimes as low as 0.1% of total airflow, but these are rare outside critical facilities.
“If you wanted to go the extra length and say we’re going to be a half a percent, do your job. Get it done right,” he said.”
Why not just stick to SMACNA’s tried-and-true standard? “There’s nothing wrong with that. It works. It’s worked for decades,” Kelly admitted. But, “why can’t we be better? You know, we’re always looking for things to be better, more efficient. Why can’t we be better?”
The Price of Leaks
Behind every loose joint and unsealed seam is a cost. Not just to comfort, or to the delicate pressure balances in labs and hospitals, but in cold, hard dollars.
“Think about how energy rates have gone up over the years,” Kelly warned. “Here you’ve had a building that was built 25 years ago, and your energy use is going up and up and up, and you get this bill every month that goes up and up and up, and it’s all related to the fact that we didn’t duct seal this system and have it tested back in the day.”
Kelly’s approach is straightforward, bordering on stubborn. “If you’re going to put together a system, take pride in it. Put it together right. And make the leakage to where it’s not impossible, and it’s not outrageous. Put the system together so that we have the least of our worries on the job would be duct leakage.”
He’s not above lending a hand – or a test rig – to a contractor, either. “Normally, what we’ll do depending on how our relationship is with the client, asking or the contractor—we have a great relationship, I’ll deliver it as a, you know, a token of gentlemanship and professionalism.”
It’s all about the team mentality. “If we’re partners on the job and we’re getting jobs done, we like the team method.”
A question from the audience: should negative ducts be tested to negative pressure? Kelly’s answer is quick. “No, the standard does not differentiate whether you take a negative ductwork, exhaust ductwork and test it on a negative condition or a positive. It’s going to leak one way. It’s going to leak both ways. The only thing time that changes is on an air handling unit, where you have in swing doors and out swing doors… No, there is no standard to which you should say positive or negative on supply or exhaust ductwork.”
Specialized Testing, and the Odd Case
Not every leak is about air. Sometimes, it’s about odor. Kelly once used a duct leakage test rig –
“almost like a leaf blower” – to find the source of sewer gas smells in an office building. Introducing theatrical smoke to the plumbing vents, he watched as it wafted up through the gaps between toilets and floors. “So you go in a bathroom and there’d be hovering smoke or theatrical smoke on the floor. We found out that the traps were in the toilet and not in the piping, so that gasses were coming up, seeping out and effervescing in the bathrooms. And it was all of the seals between the flange of the floor and the bottom of the toilets, not all of them, but several of them.”
The Takeaway: Craft Matters
As he wrapped up his talk, Kelly returned to first principles. “It’s called quality and craftsmanship. If you’re going to put together a system, take pride in it. Put it together right.”
His advice for the next generation of engineers and contractors is simple: “Just apply the 1% factor and you should be good.”
The air may be invisible, but the difference, Kelly insists, is clear as day.
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