An ultraviolet light placed in the return duct is used in Fresh-Aire’s Airborne Duct System. It kills bacteria that can cause odors or spread infections in places such as hot-yoga centers. Photo courtesy of Chad Clark.

Keeping building humidity levels and temperatures in check is often tough under normal conditions. 

But try designing a system that’s made to maintain an ambient temperature of 110°F and humidity made to make occupants sweat. 

That’s the scenario Chad Clark is typically faced with as president of Hot Yoga Studio Design and Services in Scranton, Pa. Clark is a consultant to the growing hot-yoga industry. 

Hot yoga is similar to regular yoga in that exercises are designed to increase mental and physical strength but with one key difference: the exercises are performed in very humid rooms where temperatures can be as high as 130°F. Stretches and stamina-building workouts are done in environments made to mimic the weather of India, where yoga originated centuries ago. 

Maintaining temperatures that high require an HVAC system capable of discharge temperatures up to 250°F. Few mechanical engineers or contractors fully understand how to design or install such systems, Clark said. 

“Hot-yoga studios, beyond any doubt, are the toughest design and installation project in the HVAC industry,”î he said.  “This is a unique application that most HVAC manufacturers want nothing to do with because occupied spaces above 92°F puts them into more stringent UL (Underwriters Laboratories) classifications and code levels.” 

Clark should know: his family owned an HVAC contracting business when he was growing up.

Improper work can lead to fires, code violations, sanitation issues and even evictions of such businesses. The collapse of a shopping center roof in Arizona was blamed on a hot yoga studio, he said. 

“I’ve had hot yoga studio owners call me when their furnace vent assembly caught fire or just completely melted because of specification or installation errors,” Clark said. Switches and a lot of HVAC devices “survive about one week in a hot-yoga supply air duct.” 

When you have hot and humid environments designed to dilate blood vessels and help stretch muscles, a side effect is that they’re also ideal for the growth of potentially disease-causing bacteria. 

That’s where the bacteria-fighting effects of an ultraviolet germicidal irradiation light system come in. In his designs, Clark uses the Airborne In-Duct System from Fresh-Aire UV of Jupiter, Fla. 

When ultraviolet systems are typically installed in places like hospitals and schools, they are placed in the supply air ducts perpendicular to airflow and parallel to air-conditioning coils. In his projects for hot yoga studios, Clark prefers to put the lights inside the ductwork with multiple 60-inch lamps in line with airflow to create more exposure to the germ-killing lights. 

Because of the hot supply air temperatures usually found in hot yoga studios, Clark prefers placing the lights in the cooler 130°F environment of the return-air ducts. He also designed the power supply to be mounted outside of the duct.

On his projects, Clark designs systems where outdoor-air levels exceed those recommended by the American Society of Heating, Refrigeration and Air-Conditioning Engineers’ indoor air quality standards. 

Clark usually uses General Electric Co.’s Teleaire sensors to increase outdoor air above 20 cubic feet per minute per person when carbon-dioxide levels warrant. He has started experimenting with his own system that monitors multiple conditions simultaneously. 

If ductwork serving a hot yoga studio is not properly sealed, it can grow mold or fungi and eventually may threaten the structural integrity of the building, Clark said. 

“Enveloping the entire studio in a vapor barrier is critical,” he said.”Then to withstand the 70-degree operating differential we build the walls and ceiling with structurally insulated panels, which are similar to refrigerated walk-in coolers.”