# Is there a solution for horizontal hood duct?

Discussion in 'Plumbing Forum' started by ilyaz, Feb 24, 2010.

1. Feb 24, 2010

### ilyaz

#### Well-Known Member

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We are putting in a range hood in the kitchen. The X in the photo shows its approximate location. We want to have a horizontal duct as shown. However, the vertical studs are all 3.5" wide. We can't make the wall thicker since in this case we won't have enough space for the cabinets. Is there any way of feeding some sort of hood duct horizontally as shown without extending the wall?

If not, we will consider either a vertical duct or no duct at all, but that would be Plan B.

Thanks!

2. Feb 24, 2010

### Wuzzat?

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What dia. vent pipe is recommended for that distance?
How deep are the cabinets?
What's on the other side of the wall?

Last edited: Feb 24, 2010
3. Feb 24, 2010

### ilyaz

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The hood we're getting is this: http://broan.com/ImageLibrary/broan/pdf/InstallGuides/626978C.pdf
It states that for horizontal it's "3¼ x 10 only"

The bottom cabinets along the hood wall is about 25 3/4".

On the other side are two bathrooms.

4. Feb 24, 2010

### Wuzzat?

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If you can stand losing 3-1/4" out of your 25-3/4" deep cabinets you can run the duct through them.
This rectangular duct is 32.5" in² in area. If you can fabricate a duct 1" or 2" deep by whatever height it takes to make the same cross sectional area, that might work and it would hardly infringe on your cabinet depth. But, people usually don't make ducts shaped like this, and probably for good reason.

Maybe you could run several small round ducts to make up the duct area.

This hood has uses up to 300 CFM, which would be an air velocity of 300/[32.5/144] = 1400 FPM in that duct. I'd think air moving that fast would be noisy.
You might want to use
Engineering ToolBox
or other sites to check how well different duct shapes will work.
Maybe at the distant end you'd need a booster fan.

Work all this out before you lift a hammer.

Last edited: Feb 24, 2010
5. Feb 24, 2010

### ilyaz

#### Well-Known Member

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Hmm, I need to think about this one. Actually, I would be cutting through the wall cabinets not the bottom cabinets, and the wall ones are certainly not as deep (not sure about their exact depth).

Are you saying that two ducts with the same area, lengths and number of turns are identical in terms of how well the air pushed through them, how loud they are etc?

Thanks.

6. Feb 24, 2010

### Wuzzat?

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Most of our wall cabinets are 12" deep.

The total area of separate ducts may have to be more than 32.5 sq. in.
The engineering site may tell you how many of what size round ducts is equivalent in resistance to the rect. duct.
You'd have to have a sheet metal shop make up a manifold to go from the hood opening to these round ducts, or you could do it yourself. I'd make a cardboard mockup first. If you don't round the corners air turbulence messes up the calculations and makes noise.

Last edited: Feb 24, 2010
7. Feb 24, 2010

### inspectorD

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Are there soffits going in above the upper cabinets? and which way do the floor joists run.

8. Feb 24, 2010

### ilyaz

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No soffits.

Joists parallel to the red line in the photo (I think)

9. Feb 24, 2010

### inspectorD

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If you can, run the ductwork in the joist cavity, just sheetrock the inside of that bay for fire codes...check with your local building official first.

Other than that, they also make downdraft hoods..which is better than nothing.But \$\$

10. Feb 24, 2010

### Wuzzat?

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Last edited: Feb 24, 2010
11. Feb 25, 2010

### inspectorD

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As long as you like takin a shower with the ductwork...that would be fine.
From actual experience, I can tell you, those walls are both the back walls of the showers in the bathroom. Look at the plaster pressed through the wire mesh...and the bottom of the tub. Then the bottom of the other has the ol lead flashing at the base..on the other side of that...I'm guessin tile.:2cents:

12. Feb 25, 2010

### Wuzzat?

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Good eye!

I guess it's against Code to use a plumbing vent pipe as a range hood vent pipe.

Why not run a vertical 3-1/4" duct between the studs, up or down, until you can go horizontally, with maybe a 24vac booster fan at the distant end?
If Broan won't help with this, ask them for the Fan Curve
http://www.greenheck.com/media/articles/Product_guide/perf_basics.pdf
for this hood blower and use the Engineering Toolbox to calc. the duct airflow resistance.

Last edited: Feb 25, 2010

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