Cathedral shaped vents require a 4th measure.
But it is not as difficult as it may seem.
First ignore the odd shape of the opening.
And don't look at the triangle top.
Treat this as a rectangle hole first.
Get the width first and double check in a few different places.
The smaller measure is ideal for ordering.
The height should be measured in the center only as it is the highest point.
The extra measure is of the side leg height.
Check both sides and use the smallest measure.
These 3 measures make up the front dimensions of the Cathedral Louver Vent.
And are referred to as "opening size" for ordering.
For this, the vent face will be reduced 1/4" per side to make a good fit and easy install.
To get the the "tip to tip" measure, it requires measuring the vent itself.
The width and height are standard.
Most forget the vent has a side leg measure.
Using the side leg measure instead of the top angle is much more accurate.
And much easier to verify.
That just leaves choosing a depth for the vent.
If there are any questions not answered here
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