duct work questions for installing kitchen hood vent

cedar32November 25, 2009

1) For the duct work, do you use galvanized sheet metal rigid duct?

2) When connecting sections do you use duct tape to hold sections together and that's it? or do you also screw the sections... or use clamps?

thanks... any other info that can be shared would be appreciated.

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guadalupe

rigid duct is best and using 1 screw per section before duct taping also making sure you have a back draft damper somewhere in the duct run or on the roof or wall cap

    Bookmark   November 25, 2009 at 11:06AM
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cedar32

thank you for the reply, Guadalupe.
The vent cap where the duct exits the building has a baffle (swinging door)... I'm assuming that's what you mean by a back draft damper.

When installing the ductwork, can the duct go up against and be strapped to wood members or must there be any clearances?
Thanks

    Bookmark   November 25, 2009 at 2:23PM
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bldn10

Is it OK for me to use a few feet of aluminum flexible ducting (not the slinky kind) from the hood to minimize turns and angles? It will connect w/ rigid up through the 2nd floor and out the roof.

Bill/Memphis

    Bookmark   February 6, 2010 at 10:05AM
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antss

rigid duct

screwed

no cloth duct tape - use fiberglass tape painted with duct sealing mastic.

strapping to framing ok.

flex not recommended as it really impedes airflow. If you must, limit it to 1 foot or less.

    Bookmark   February 6, 2010 at 3:03PM
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live_wire_oak

What Antss said. Except the bit about the flex duct. NO flex duct of any variety. It's a fire hazard as the ridges provide surface for grease to accumulate. Only rigid metal ducting allowed. Required by code actually. Sealing the seams with duct mastic and covering them with metal tape is usually a little bit easier than using the mastic coated tape. YMMV.

    Bookmark   February 6, 2010 at 6:23PM
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buffalotina

OMG, I am reading this about 4 months too late... I think my guys just screwed the sections together and that was it.... am I going to die? Is that a big deal? I figure my fan is so powerful it will whip everything past the seams out and out the door... no? What are the consequences - grease between the joists? Thank you in advance.

    Bookmark   February 6, 2010 at 10:06PM
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bldn10

If I don't use the flex I will have to use several of those multi-segment angle pieces that aren't smooth on the inside either and add more joints. Still no?

Bill/Memphis

    Bookmark   February 7, 2010 at 9:57AM
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antss

bldn - you cannot look at these things with a casual eye and a shade tree engineering perspective. The flex duct's resistance to airflow with all of those ribs even if it's straight is many times grater than a segmented angle piece. It's a fairly complex fluid dynamics calc, so just take our word for it that flex duct is bad news.

    Bookmark   February 7, 2010 at 1:49PM
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mirrorman

The liner I'm looking at has two 6" top exhaust vents (prestige powerpack). I'm limited by space in the ceiling joists and would like to continue with two 6" ducts, capped outside. A single 8" or 10" won't fit. I understand that the single larger duct can carry more volume, but the choke point is those two 6" exhaust vents anyway, right? One 6" is already in place, so running another down an adjacent joist would be relatively easy. Comments?

Dan/Memphis

    Bookmark   February 7, 2010 at 3:33PM
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kaseki

One would have expected Prestige to provide some advice, but without it, I recommend you match six-inch vents with six-inch ducts. Larger ducting reduces resistance but also slows down the air velocity. Commercial ducting requires 2000 ft per min air velocity to limit the amount of grease that will condense. According to some sources I've read, residential velocities should aim for the 1000 to 2000 ft per min range.

The two six-inch vents can be merged into a duct with the same cross-section, around 8-inches, but only if both power packs are powered at the same time. Otherwise, keeping the velocity up requires individual ducts.

A call to Prestige may be desirable.

kas

    Bookmark   February 7, 2010 at 4:39PM
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inter_alia

Fantech makes some clamps with rubber for hooking the duct to the fan that prevents vibration from transfering down the duct.

American Aldes website has a Kitchen Ventilation diagram that may be of help. They sell flex duct for your application that does not restrict flow and reduces sound. They note it is not UL listed. A grease filter would keep grease out of the system.

Here is a link that might be useful: Fantech RC6 Clamps

    Bookmark   February 7, 2010 at 9:54PM
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bldn10

2 guys from Memphis, odd.

This is a stupid question but my hood is not in yet and I want to get the ductwork going. Is there a convention re rigid round duct starting? I.e. does the appliance always have either a male or female opening? If so, which way is it? If so, will the final piece, the roof cap, follow that convention? What is the best way to join sections where one had to be cut?

Bill/Memphis

    Bookmark   February 9, 2010 at 4:53PM
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judeNY

There is a rigid duct piece that is adjustable to any angle. I found it very useful in making those odd bridges between straight sections that would require several fixed angle connectors. With the adjustable I was able to have slight gentle curves instead of multiple fixed angles. I bought it in HD in the section with all the other duct segments.

    Bookmark   February 9, 2010 at 8:58PM
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judeNY

There is a rigid duct piece that is adjustable to any angle. I found it very useful in making those odd bridges between straight sections that would require several fixed angle connectors. With the adjustable I was able to have slight gentle curves instead of multiple fixed angles. I bought it in HD in the section with all the other duct segments.

    Bookmark   February 9, 2010 at 9:00PM
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b_proark_yahoo_com

We are installing a vent hood in our kitchen which has a 10" rectangular opening and a duct coming from the ceiling with also a 10" rectangular opening. How do we make this work? Are there any adaptors that will work for this?
Pam

    Bookmark   December 9, 2010 at 11:36PM
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