"The question was, does cleaning the duct really help in terms of energy? And the answer is yes," explained Dr. Mark Hernandez, P.E., a professor at the University of Colorado Boulder and one of the study's authors. "Obviously, it's dependent on how much dirt work you have – the more you have, the better the benefit."

In extensive testing at a large university building, researchers discovered an unexpected benefit: dramatically improved system stability. Modern HVAC systems rely on networks of sensors and variable airflow valves (VAVs) reporting to central control systems. In dirty systems, these VAVs constantly hunt for the right position, repeatedly opening and closing as they struggle to maintain proper airflow.

The research team took a methodical approach to understand exactly which cleaning interventions delivered the biggest benefits. In their previous study, they cleaned systems in stages to isolate the specific impact of duct cleaning from other maintenance like coil cleaning. This staged approach helped quantify the individual contribution of each cleaning intervention to overall system performance. For their current work in Denver schools, they've shifted to comprehensive cleaning of entire systems, including both ducts and coils, to evaluate real-world outcomes in active learning environments.

"When you clean the ductwork, the VAV response time and system stability is way better," Hernandez notes. "The dirty system had the VAVs opening and shutting and opening and shutting. But after cleaning, they were all opening together, all closing together. It behaved like a symphony orchestra."

This improved stability has major implications for both energy efficiency and occupant comfort. When VAV systems operate more smoothly, they waste less energy overshooting and undershooting their targets. They also maintain more consistent temperatures and ventilation rates throughout the building.

The findings come at a critical time, as facilities face mounting pressure to reduce their carbon footprints while simultaneously improving indoor air quality in the wake of the pandemic. A parallel study currently underway in Denver Public Schools is examining the effect of duct cleaning on indoor air quality and respiratory exposures. The research team selected four schools with the poorest ventilation performance, as measured by their air exchange rates, to evaluate how cleaning might improve both air quality and ventilation effectiveness.

Early observations from the schools study have revealed concerning patterns. To save energy, many schools completely shut down their HVAC systems overnight. When systems restart in the morning before students arrive, some classrooms experience dramatic spikes in airborne pollutants as settled dust and contaminants are re-suspended.

"Whether it's in the classroom or in the ventilation system itself, you get this stuff going around and around in circles – being suspended, settling, re-suspended, settling, re-suspended," Hernandez explained. While the hypothesis is that proper cleaning will help address these pollution spikes, the exact magnitude of improvement remains to be quantified.

The research suggests that regular HVAC cleaning could be a crucial and often overlooked tool in building decarbonization strategies. Unlike many energy efficiency upgrades that require substantial capital investment, duct cleaning is a relatively straightforward maintenance intervention. The benefits scale with system size – larger ductwork systems showed greater improvements in airflow after cleaning, while smaller systems benefited more from coil cleaning due to enhanced heat exchange efficiency.

The emergence of affordable Internet of Things (IoT) monitoring technology has made it possible to precisely measure these improvements, providing facility managers with concrete evidence of cleaning's impact on system performance.

"Only through thoughtful monitoring can such optimization be achieved and confirmed," Hernandez emphasized, noting that buildings face dual pressures to improve indoor air quality while reducing energy consumption.

The study suggests that sometimes the most impactful solutions aren't about adding new technology – they're about maintaining what's already there. The challenge now lies in integrating these findings into comprehensive building management strategies that consider both the immediate and long-term benefits of regular HVAC system cleaning.

Read the study here.