9007 inside vs outside measurement measuring basics blue 1 do you need the inside opening, outside duct size, or insulated outside size? i'm checking inside vs outside measurement. i measured the field condition and want to verify the reference point before i act. do you need the inside opening, outside duct size, or insulated outside size? measurement question: inside vs outside measurement. i have the location, photo, and measured reference point ready. who should verify before this becomes cut, ordered, drilled, or covered?