18" X 18" ALUMINUM RETURN FILTER GRILLE FOR 1" FILTER - EASY AIRFLOW - LINEAR BAR GRILLES 18" Round Duct Pipe 3 * insulation density is

3 * insulation density is 30kgs/cbm = 0

then you'll need a 14-inch round vent

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18" X 18" ALUMINUM RETURN FILTER GRILLE FOR 1" FILTER - EASY AIRFLOW - LINEAR BAR GRILLES 18" Round Duct Pipe 3 * insulation density is+ Product Details Size 18"w X 18"h is the size for the duct opening measurement only, [Outer Dimensions: 20. 5"w X 20. 5"h] Actual Filter Size 17 3 4"w x 17 3 4" x 1" High Quality High quality rust free, strong aluminum construction with smooth finished edges for easy and safe use; Filter grille features a user friendly plastic latch that requires no screwdriver for opening. Installation Location Sidewall and ceiling. Design Heavier gauge than needed,