Range hood install panic

12 years ago

Oy vey y'all. The cabinets are coming Friday and I need some serious help with my range hood install.

I have a 30" Bosch with 450CFM that I bought off ebay. It came with supposedly a transition... that I am nearly 99% sure is not the right piece and has nothing to do with my hood. Maybe I'm not seeing it but I think this is for joining two vents together not for connecting venting to a hood.

On the hood, the size of the knock out opening is 3 3/4 by 7 3/4... which is totally not anything 'standard' that I'm finding in duct work. Here's the opening:

The manufacturer sells replacement parts for the transition which I could buy, but I'm worried it won't fit in my cabinet. The piece is for a transition to an 8" round pipe. There is a stud directly behind the hood's center so I planned to use two 90 degree elbows to offset the vent by a few inches. Since the run is so small (it's going up into a cabinet, hanging a left and going out the wall) I think this is fine. BUT the cabinet is only 15" and it is open above the cabinet, so I'm nervous that I won't be able to fit the transition + 8" 90 elbow. The elbow is about 10" high so that only leaves me like 3"-4" for the transition which according to this pictures seem like it might BARELY make it.. but it'd be crazy close. (Part 0101)

Questions:

Is 6" pipe okay for a 450CFM hood even if the manufacturer transition comes at 8"? I found all the pieces I would need at a home improvement store and I'm pretty sure they will fit in the cabinet, though attaching to the hood seems a bit dicey as I would have to snip and fold the ends of the transition I bought and screw through makeshift flaps. Is that okay? Do I just do that, tape it with metallic tape and call it a day?

Is a hole 3 3/4 by 7 3/4 a standard 3 1/4" x 10" connection and I just don't get how duct work attaches? Do I need the manufacturers transition?

What happens if I buy the manufacturers transition and that plus an 8" elbow won't fit height wise in a 15" cabinet?

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Comments (5)

angie_diy
12 years ago
(Sorry if this is a double post; my browser ate my first message!)

I think I can help, but only a little. I am pretty sure that the mystery item in your first photo is an adapter for a ventless installation, that is, one where the air is recirculated back into the room. The piece in the photo vents the air to either side of the chimney.

As for the size, I think a 6" duct would be okay (although, as you point out, 8" would be better). The cross sectional area of your 3.75x7.75" opening is the same as a 6.0" round duct. I doubt this is a coincidence.
sombreuil_mongrel
12 years ago
If you look in the duct aisle at Home Despot, you may find a 4x12 "boot" (transition from round duct to grille, usually installed in floors or ceilings) that can be modified to attach to your vent. I don't think you could find a 4x8 boot at HD, though if you have a large supply house in your area, go ahead and ask them. You want an inline boot with a straight transition, not one with a formed-in 90. There are both types, as well as a third type with the inlet (outlet in your case) of an end. Depending on how you're ducting this that could be useful to you, too.
To make one of these work, you cut the corner seams and bend it flat to make the screw flange, then make sure it is well-taped to the vent for a tight seal. To give you an idea of the shapes, link below.
Casey

Here is a link that might be useful: googlr shopping page of boots
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Circus Peanut
12 years ago
Just to throw in that while 6" duct will work, 8" will be a lot quieter if you have a few elbows in there. We have the same setup and switched from a hood with 6" to a hood with 8" and the larger hood, although more powerful, is actually quieter with the larger duct.

You can use any boot that fits (as long as you use rigid ducting not the flexible kind) but make sure it has the flap that will help prevent the backdraft of cold air in from the outside. The outside cap will do this, too, but most vents come with another one right at the transition from the fan.

Yes, you snip it and screw it on, tape it with metallic tape (not "duct" tape!) and call it a day. :-)
brickton
Original Author
12 years ago
Angie, seriously how did I miss that the hole is nearly exactly the same square inches as a 6" pipe. Now I'm questioning where I got the 8" number from. I think 6" is the right size since 3.75 * 7.625 ~ 3.14159 * 9 ... yay.

Casey, that is exactly what I bought (a 4" x 8" from 6" round register transition) but I was questioning if my thought of snipping and bending flaps was right or not. Thank you so much for confirming that. Though in your google search the 'end' boot looks even better because it would combine the rectangular to round transition and one of two 90 degree elbows into one piece. I might try to find one of those locally just to save some space in the cabinet and have fewer seams.

circuspeanut-
Thanks! I would prefer the 8" but I don't think I can fit the necessary elbows in the cabinet... unless I do the end boot + 1 elbow... hrmn. I will look into this as I don't want to end up with a hood too loud to use comfortably.
brickton
Original Author
12 years ago
Okay so a couple deep breaths, some great advice and another trip to the hardware store (the blue one) and I now have a better plan.

I finally found a reasonable 8" vent cap (that wasn't $50+) with a damper, the end boot, another spring loaded damper (because the cap one isn't spring loaded and my boot won't have one like cp mentioned above) all for Whew... now I just need to work up the courage to cut holes in things I paid a lot of money for to attach all this.

Thanks again everyone.

Range hood install panic

Comments (5)

angie_diy

sombreuil_mongrel

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Range hood install panic

Comments (5)

angie_diy

sombreuil_mongrel

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Circus Peanut

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