Decribes how the 19 floor 76m high Arts Tower at Sheffield University is having its energy use characteristics investigated. Illustrates a typical floor plan. Describes and illustrates a component pressure testing rig todetermine the infiltration coefficients of the vertically sliding windows. Treats the criteria determining the rig design and the air flow measurement procedure. Treats tests on windows where the sealant did and did not appear defective, the overall values of window coefficients, testing of a weatherstripped window, the payback period for weatherstripping the windows. Finds significant deterioration of the window joints, to the extent where acceptable payback periods can be obtained with remedial measures.