Question about ducting for range hood

14 years ago

A contractor has told me one thing but it doesn't seem intuitive so I would like to ask other experts. Apologies if it's been addressed before (it seems like a familiar question but I can't find a thread about it).

Is it OK to take a vent going up through the roof around a couple of ~90 degree bends, or is it better to go straight up if possible? The question is whether, if we relocate the range, we could use the same vent hole that's already cut in the roof, or if we'd need to cut a new one. If we move the range, it would shift 6-10 feet, depending on layout. So it would have a horizontal (or diagonal upward) run through the attic as well as the turns. It's a one-story house. If it matters -- we have an electric coil stove and won't ever have gas (if we change it will be to induction). Our current hood is I think 400 cfm max and that has been working well for the way I cook. The duct we have now runs straight up with a only little bend of a few inches to get around a ceiling joist.

Thanks --

Featured Answer

weedmeister

14 years ago

two 45s are better than one 90. Several mild bends are better than one big one.

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Comments (6)

davidro1
14 years ago
two 45 or 90 angle bends?

extremely small diameter duct or not?

If your new exhaust is a lot more powerful than the old one, you really want to make sure you get the duct size right-sized. Then, secondly, it may be also good to have two 45 degree bends instead of two 90's. Bends are not a massive problem. Total diameter is.
User
14 years ago
If you have bends and a longer run, then you will need a more powerful hood than if you did a shorter run that was a straight shot. You want to avoid any 90 degree bends in a ventilation setup if you can. They drastically affect the flow dynamics and lead to increased grease deposits on the ductwork's interior.
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northcarolina
Original Author
14 years ago
Thank you both! The contractor had told me that it would be fine to run a duct to the existing roof hole from a different location, but I wanted a second opinion. Sounds as though it is OK as long as we make sure the hood and the duct are both adequately sized, and I will keep in mind that our current setup might not be. What you both say makes perfect sense.

I don't know the angle the bends would be (depends on the final layout) but I think that avoiding right angles would be possible considering that we don't have to go through a wall first. Just straight through the ceiling and then over to the hole in the roof through the attic.

Thanks again!
northcarolina
Original Author
14 years ago
Thanks, weedmeister, I'll keep that in mind!
jackals
14 years ago
Concur with the previous responses on bends - additional tip, sounds like you are sticking with 400 to 600cfm, in which case try and run minimum 8" round "solid" (avoid the flexible duct at all costs - creates a lot of air turbulence and degrades airflow)(effective area of duct to be around 50sq inches if you have to use something other than round duct).

Here is a link that might be useful: Ducting for range hood