As a young HVAC technician in the late 1970s, I often faced a curious contradiction. Customers who had purchased our "best" air cleaners were dissatisfied, complaining about dust still settling on furniture or visible particles floating in sunlit rooms. Despite their investment, the air in their homes didn’t feel “clean” enough. I checked and rechecked everything: the voltages on electronic air cleaners, the media filters, and even advised running furnace fans continuously. Still, the complaints persisted until they eventually resigned themselves to subpar results.
Fast-forward three decades, and my perspective shifted completely. Armed with a laser particle counter, I began testing the actual performance of air filtration products, including those we installed and those sold by competitors. The results were eye-opening. Most filters fell far short of their advertised efficiency. One exception stood out: the Perfect 16 by IQAir, which consistently delivered as promised. A close second was Lennox’s Healthy Climate Carbon Clean 16. The rest ranged from mediocre to downright ineffective, with some removing as little as 5% of fine particulates. Non-particulate filter products, like bipolar ionizers and photocatalytic oxidizers, were particularly disappointing, failing to meaningfully reduce airborne particles in homes.
Although we loved the Perfect 16, it had a major limitation: its size. It simply didn’t fit in most residential HVAC systems. Out of frustration—and inspired by customers’ needs—I decided to invent my own solution. Enter the NovusAer air filtration unit, which I spent five years developing and field testing. Unlike most filters, the NovusAer could fit in nearly any home and captured 100% of PM 2.5 particles, obtaining near HEPA efficiency while achieving a pressure drop that of standard residential media filters.
But even the best filter isn’t enough when there’s a bigger issue at play: air infiltration. This became clear when we installed a NovusAer unit in the home of a boy with severe respiratory issues. Although the filter worked as designed, the air quality in the home was still suboptimal. Why? Infiltration air—dirty, unfiltered outdoor air seeping into the home—was diluting the effectiveness of the system.
The Infiltration Problem
According to a 2002 Lawrence Berkeley National Laboratory study, the average pre-1994 home experiences 1.18 natural air changes per hour (ACH nat). For a 1,500-square-foot home with a basement, that translates to roughly 295 cubic feet per minute (CFM) of unfiltered air entering the home. Even with a high-performance air filter delivering 1,200 CFM of clean air, the infiltration reduces the system’s effective air filter efficiency by 25%. A MERV 16 filter might deliver the equivalent of MERV 11 performance in such conditions, while a MERV 13 filter might only reach MERV 10.
A Game-Changing Solution: Depressurization Ducts
To address this, we began incorporating a simple but effective modification: a depressurization duct. By installing a 6-inch duct with a manual adjustable damper from the outside of the home to the HVAC system’s return air plenum (upstream of the filter), we could filter incoming infiltration air. During setup, we adjusted the damper to equalize the pressure difference between the inside and outside of the home to 0 pascals, ensuring no unfiltered air was seeping in.
When we revisited the home with the boy who had respiratory issues, the improvement was dramatic. The family reported significantly better air quality, and their son’s symptoms eased noticeably. From then on, we offered depressurization ducts with every NovusAer installation, later standardizing on 8-inch ducts for even better results.
Reducing Visible Dust
Beyond health benefits, depressurization ducts help with another common complaint: visible dust. Much of the dust settling on furniture comes from unfiltered infiltration air. By filtering all incoming air, these ducts reduce the dust load dramatically. While it’s not a flawless solution, it’s one of the most effective approaches we’ve found.
Real-World Results
Even in challenging environments, like my own home in Salt Lake City, depressurization ducts have proven their worth. Our high mountain valley often suffers from severe air pollution due to temperature inversions, yet my indoor air quality remains pristine. With a furnace running at just 25% continuous fan speed, my air monitors consistently read 0 PM 2.5 particles, regardless of outdoor conditions. Customers with similar setups have reported equally impressive results.
The Takeaway
Achieving clean indoor air isn’t just about choosing the best filter. It’s about addressing the broader system, including the impact of air infiltration. By combining high-efficiency filtration with a well-designed depressurization duct, homeowners can enjoy truly clean air—free from harmful particulates and visible dust—no matter the environment. If you’re serious about air quality, it’s worth investing in a comprehensive solution that tackles the problem from every angle.
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