... and total heat exchanger are available. FAN SECTION AIR FILTER SECTION Coarse filter---corrugated plate type, 25mm or 46mm in thickness, ... or non-woven fabrics, efficiency rating at G2, G3. Medium filter---bag type, made of fire-proof chemical fibres, efficiency rating ... at F5~F8.High-medium/sub-HEPA filter---bag or pleat type, made of fiberglass, efficiency ...