I HAVE A 35000 BTU AC,THAT GOES TO A SYSTEM THAT IS OUTSIDE,IT HAS A OPENEN FOR BLOWING THE AIR INSIDE THROUGH A APPROX. 12" OPENING,FOR DUCT WORK. I NOT SURE THE SIZE OF THE OPENING.I BOUGHT TO USE BUT NEVER DID INSTALL. CASH ONLY,YOU CAN CALL ME, ,PLEASE LEAVE MESSAGE IF I DON'T ANSWER.