A drive cleat joins the ends of two sections of ducts and is then hammered flat to lock the joint.

Rectangular metal duct connects the holes in my kitchen ceiling and exterior wall. I assembled the duct out of three-foot long flat sections, folding two pieces into ell-snapped walls and joining those to form a section of duct. To join the two sections I needed together, I used S-cleats on the long sides drive cleats on the short sides as outlined here. I then sealed the seams with mastic, which seemed to take forever to dry. For the long seams, I opted to use a high-quality foil tape, an approach I’ll use for any future duct work I do given its ease of use and instant gratification. 

Once the duct was assembled, I carried it outside and slid it into the exterior hole, taking care to  avoid disturbing the plaster ceiling. A vent cap finished the exterior. At the other end, I installed a 90-degree square to round adapter and ran a short section of 6″ round duct to the microwave. Venting to the outside makes a world of difference in the kitchen, removing humidity and odors in a way that our old recirculating fan couldn’t.