with special soak-off cleaners, where the entire plate array is removed from the precipitator and soaked in a large container overnight, to help loosen the tightly bonded particulates. A study by the Canada Mortgage and Housing Corporation testing a variety of forced-air furnace filters found that ESP filters provided the best, and most cost-effective means of cleaning air using a forced-air system. The first portable electrostatic air filter systems for homes was marketed in 1954 by Raytheon. See also Scrubber Air ionizer Ozone generator Air Purge System References External links American inventions Air filters Chemical equipment Pollution control technologies Air pollution control systems Particulate control Gas technologies Solid-gas separation