in fig5 in the configuration of fig5 the short circuit hood 500 includes air volume control dampers 506 508 that regulate respective flows of make up air i e through make up air collar 504 to the supply plenum 108 and conditioned air i e through hvac unit collar 510 to the conditioned air duct 118 conditioned air supplied to the conditioned air duct 118 is used to create a vertical curtain of fresh air at the front of the hood thus air from the duct 118 is discharged at outlet 516 through a grill or diffuser 517 meanwhile make up air e g outside air is provided via make up air collar 504 to supply plenum 108 and then to the recess 102 of the hood through a grill or diffuser 114 fumes and other gases in the recess 102 can be exhausted by a fan connected to exhaust duct collar 502 which withdraws the fumes from the recess 102 by way of filter 148 and exhaust plenum 104 referring now to fig7 the retrofit of short circuit exhaust hood 500 can begin at 702 with disconnecting the make up air intake collar 504 from the make up air supply not shown at 704 the make up air volume control damper 508 can be removed an optional fire damper 602 can be installed in the collar 504 or the upper portion.