How can I shorten this metal duct (used for a downdraft range)?

January 25, 2014 2:24 PM

I have a very well-constructed downdraft duct that is a few inches too tall. My normal efforts to try to cut it down or remove a piece have been unsuccessful. The downdraft range I bought doesn't line up with the duct and is about two inches too tall. Is there some way I can get the two to play nice?

I have a house that has a duct for a downdraft from a counter-mounted range. The kitchen is on the first floor, above a basement, and the duct goes into the floor turns 90 degrees in the basement, and runs out the side of the house. The previous range did not have a downdraft feature and only sat a couple of inches below the thickness of the counter.

Here are some pictures of the duct.

Here's the problem: I bought a new (well, used from Craigslist) cooktop that has a downdraft blower. The blower outlet on it is permanently joined to it and is about two inches too long plus it is offset about four inches. This means that the cooktop doesn't sit down on the countertop and the blower's outlet doesn't go directly into the duct.

I assume I will need to buy ducting to carry the output down into the duct. The problem is that my existing duct is apparently steel or very rigid aluminum. My snips don't do any damage. Removing the tapered part would be ideal but I can't seem to get it to budge. There is a second floor above the kitchen with virtually no gap between the floors so running a normal cooktop vent would be difficult. I'd like to not have to replace the entire duct since it is rather firmly affixed to the house but that can be an option.

Does anyone have any ideas for how to make a round peg into a slightly shorter round peg?

Blowtorch? That would be awesome.

posted by fireoyster to Home & Garden (5 answers total)

If your snips can't hack it, your other options are better snips, a hacksaw, a metal cutting blade in a Sawzall-type recirocating saw, or an abrasive cutoff wheel in an angle grinder. The abrasive cutoff wheel is the easiest, but also the riskiest as it will throw sparks off the steel as it cuts.
posted by jon1270 at 2:31 PM on January 25, 2014

The last section of the duct adapts it from a round to a square cross-section and has a joint connecting it to the rest which looks to me as if it could be pulled or pried apart with far less effort than it would take to cut anything.
posted by jamjam at 3:49 PM on January 25, 2014

Response by poster: Not to threadsit, but I've tried cutting the duct tape around that join and it won't move for love nor money. Do you know how they attach? Maybe I can do the reverse of that to detach.
posted by fireoyster at 3:54 PM on January 25, 2014

Ah, I see that you specified you couldn't budge it.

Try hammering the blade of a stainless table knife down between the adapter and the main body.
posted by jamjam at 3:55 PM on January 25, 2014

The thinner the blade the better, and all around the circumference; the knife will probably be destroyed. I'd guess corrosion is what's making it so hard.
posted by jamjam at 4:01 PM on January 25, 2014