Step 1
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Measure inside width and height in 3 places.
Inside Mount: take the smallest measurement.
Outside Mount: take the largest measurement.
Step 2
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Measure diagonally to check window squareness.
If the difference between the two diagonal measurements is greater than 1/4", outside mount is highly recommended.
Step 3
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Verify if there is a minimum of 1 1 /2" of flat wall surface around the window to mount the frames.
If there is enough flat surface around the window, Outside Mount is preferred.
Step 4
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Ensure there is a minimum of 5/8" depth clearance from any obstruction inside of window opening.