Blower door technology was first used to measure building airtightness in Sweden around 1977. This earliest implementation used a fan mounted in a window, rather than a door. Similar window-mounted measurement techniques were being pursued by Caffey in Texas, and door-mounted test fans were being developed by Harrje, Blomsterberg and Persily at Princeton University to help them find and fix air leaks in homes in a Twin Rivers, New Jersey housing development. Harold Orr has also been identified as a member of a group in Saskatchewan, Canada who was pursuing similar testing methods.