to the inlet of the first hood block 11 before the blower 21 the air is passed to the blow box 50 from the first hood block 11 as follows in alternative a the blow air is directed to the blow box 50 from the outlet of the first hood block 11 before the outlet air of the first hood block 11 passes through a possible heat recovery 29 the exhaust air from the blow box 50 is passed back to the outlet of the air system of the hood 15 before the heat recovery system 29 in alternative b the blow air is directed to the blow box 50 from the outlet of the block 11 after the heat recovery system 29 the exhaust air from the blow box 50 is passed back to the outlet of the air system of the hood 15 after possible heat recovery system 29 the exhaust air can then be removed from the system via blower 33 in the alternatives a and b encircled as shown in fig2 c the circulation of air of the yankee hood blocks 11 12 is connected in parallel such that there is a common outlet for the exhaust air from the first hood block 11 and the second hood block 12 air is passed to the blow box 50 as follows in alternative a the blow air is directed to the blow box 50 from the common outlet of the hood blocks 11 12 before the heat recovery system 29 if present the exhaust air of the blow box 50 is passed back to the common outlet of the air system of the hood 15 before the heat recovery system 29 if present preferably the exhaust air is passed back to the common outlet after the.