If you are looking for a free download of the Duct Sizer utility, the most reliable method is to access the legacy software archives often hosted by HVAC engineering resource sites or educational institutions.

And it was available only through an exclusive, nearly impossible free download.

“It’s not for sale,” he said. “But I can run the numbers for you. Cash only. And you never ask how.”

), which is a popular free utility, or commercial software like Elite Software's Ductsize 6.0