Measure the size of the vent to see how many glass blocks you’ll need to remove to install it.
Cut into the mortar around the glass blocks, using a razor or knife. If this doesn’t work, use a drill with a masonry bit to drill through the mortar. Break apart as much as possible of the mortar that surrounds the blocks to remove them.
Pull out the blocks and set them aside. Vacuum any dust and debris from the mortar removal.
Apply a ¼-inch line of mortar around the vent with a trowel and slip it into place between the blocks. Wipe off any excess mortar from the window with a damp cloth. Allow it to dry for 24 hours.
Apply a line of caulk around the vent to keep it airtight.