W401 plant room, I am not sure what this huge ventilation plant served after W404 was converted to office space. This plant was originally installed to serve the old computer room in the W404 area. The ducts led, via a very complex layout to what became W409 (Digital Supply) as well as W404 but it’s a huge plant for office space that became less sparsely populated as time went on. This appears to be the supply side of the plant, with the pipes presumably for heating batteries for the various branches of the main supply duct header. 24 Sep 2011.