I looked up its dimensions on-line beforehand. The top, being a 30″ cooktop, presents no problem. I was a bit concerned about the dimensions of the fan underneath and its housing. Our cooktop is in a center island and ventilation is downdraft, through a 6″ pipe in the foundation. I was concerned that there will not be enough room to add the necessary ducting to connect the ventilation fan’s exhaust port to the 6″ pipe in the foundation. Sure enough, Murphy’s Law struck and I failed to find a combination of cooktop/fan/exhaust port that would line up with the 6″ pipe.
After exhausting my vocabulary of colorful words in several languages, I decided that the only solution is to fabricate a custom “exhaust manifold” to connect the cooktop’s fan exhaust port to the pipe. The first step was to fabricate a prototype from cardboard. The prototype will then serve as the template for the actual manifold, to be fabricated from 26-gauge galvanized tin. The prototype needs to be of a material approximating the thickness of galvanized tin. It also need to be sturdy enough so the prototype’s fit and clearances and dimensions will be meaningful. I have been stockpiling cardboard-weight packaging (frozen food cartons, etc.) to use in making sewing patterns, so that’s what I used to make the prototype. Here are a few pics:
The next step was to use the prototype as a template to lay out the actual manifold on a sheet of galvanized tin (from Home Depot). A fine tip permanent marker works well on the tin. A tin snip served cutting duty, with a nibbler helping out in a couple of tricky places.
Folding is one area where I wish I had done more research. I thought that I could make reasonably straight and square folds by scribing along the fold line. As it turned out, repeated scribing with a punch didn’t make enough of an impression for a quick and square fold. As I was struggling to make the folds, patiently hammering on them like an old-time Jaguar factory worker hammering the curve into a roadster’s fender , I was wishing I had a sheet metal brake:
As it turned out, there are small sheet metal brakes that are very affordable.
I used rivets in putting the manifold together. They’re aluminum rivets, 1/16″ shank, 1/8″ maximum reach, from Home Depot.
I re-used a section of 6″ ducting from the old cooktop’s exhaust to connect the manifold to the in-floor 6″ pipe.