A blower door is a machine used to perform a building air leakage test. It can also be used to measure airflow between building zones, to test ductwork airtightness and to help physically locate air leakage sites in the building envelope.
There are three primary components to a blower door: a calibrated, variable-speed blower or fan, capable of inducing a range of airflows sufficient to pressurize and depressurize a variety of building sizes; a pressure measurement instrument, called a manometer, to simultaneously measure the pressure differential induced across the face of the fan and across the building envelope, as a result of fan airflow; and a mounting system, used to mount the fan in a building opening, such as a door or a window.
Airtightness testing is usually thought of in residential settings. It is becoming more common in commercial settings. The General Services Administration (GSA) requires testing of new US federal government buildings.
A variety of blower door air tightness metrics can be produced using the combination of building-to-outside pressure and fan airflow measurements. These metrics differ in their measurement methods, calculation and uses. Blower door tests are used by building researchers, weatherization crews, home performance contractors, home energy auditors, and others in efforts to assess the construction quality of the building envelope, locate air leakage pathways, assess how much ventilation is supplied by the air leakage, assess the energy losses resulting from that air leakage, determine if the building is too tight or too loose, determine if the building needs mechanical ventilation and to assess compliance with building performance standards.
History
In Sweden blower door technology was first used to measure building air tightness in 1977. The earliest implementation in Sweden used a fan mounted in a window, rather than a door. By 1979, similar window-mounted measurement techniques were being pursued in Texas, and door-mounted test fans were being developed by a team at Princeton University to help them find and fix air leaks in homes in a Twin Rivers, New Jersey housing development.
In Canada the initial concept similarly involved the use of a blower window, which was first utilized by G. T. Tamura in Ottawa, Canada, as part of a Division of Building Research study to test houses in Ottawa in 1967–1968 and was published in 1975.
In Canada, a team at the National Research Council of Canada's Division of Building Research (NRC/DBR) in Saskatchewan, advanced the published work of Tamura in 1975 and went from a blower window to a blower door concept used in the construction of the Saskatchewan Conservation House in 1977. The Saskatchewan group was actively involved in the development of the blower door in 1977-78 and published their findings in 1980. They made available their flow nozzle to interested companies including one from Minneapolis. Harold Orr, who had been in Ottawa in 1967 when Tamura was conducting his work, continued to work on blower door technology after Tamura published his paper. Tamura's blower window concept from 1967, preceded the Swedish work in 1977 by a decade. The first blower door was further used to test the airtightness of the Saskatchewan Conservation House built in 1977, which was tested at 0.5 ach at 50 Pa.
These early research efforts demonstrated the potential power of blower door testing in revealing otherwise unaccounted for energy losses in homes. Previously, air leakage around doors, windows and electrical outlets was considered to be the primary leakage pathway in homes, but Harrje, Dutt and Beya used blower doors to identify thermal bypasses. These bypasses were air leakage sites, such as attic utility chases, that accounted for the largest percentage of air leakage energy loss in most homes. Use of blower doors in home energy retrofitting and weatherization efforts became known as "house doctoring" by researchers on the east and west United States coasts.
The blower door first became commercially available in the United States in 1980 under the name Gadsco. Harmax started to sell units in 1981, followed closely by The Energy Conservatory in 1982.
While these blower door-testing efforts were useful in identifying leakage pathways and in accounting for otherwise inexplicable energy losses, the results could not be used to determine real-time air exchange in buildings under natural conditions, or even to determine average annual air exchange levels. Sherman attributes the first attempt at doing this to Persily and Kronvall, who estimated annual average air exchange by: