Range hood building code/best practices -> flexible or solid ducting?

[DRF99]

It's kitchen renovation time and I was wondering about venting a range hood to the outside of the house. Must you use solid ducting? Or is it OK to use flexible metal ducting?

The Ontario building code says:
(5) A kitchen exhaust duct not equipped with a filter at the inlet end shall be designed and installed so that the entire duct can be cleaned.
(6) Ductwork for range hoods and range-top fans shall be of noncombustible, corrosion-resistant material and shall lead directly to the outdoors without connection to other exhaust fans or ducts.
(7) Ductwork for range hoods and range-top fans shall be equipped with a grease filter at the intake.
(8) All ductwork shall be permanently supported or clipped to prevent sagging, excessive movement and vibration.

which seems to mean that flexible ducting is fine.

Even if it is according to the code, would you recommend it? What are they putting in new houses these days? My main concern is a buildup of grease and grunge over the years.

Cheers!

[goofball]

For our's, we have solid except for the joint between the microwave duct and the 6" circular duct as it's not 100% straight in between. If you''re able to use solid ducting, I would do that. Otherwise, minimize the use of the flexible ducting but I wouldn't say don't use it at all.

[GapBoyPCS]

I'd go with a rigid line as much as possible, only going from what I've read with some of the installation manuals of the hoods I looked at. The flexible stuff seems to decrease the air flow, which cuts down how much stuff gets sucked out.

If you have an idea of hoods you want, I suggest going to various company websites and downloading their specs and installation manuals. Most of the mid-powered hoods need at least 6-inch diameter round ductwork or a specific-sized rectangular ductwork. If the hood is going to be a fair distance from an exterior wall and/or you got to go through a fair bit of kinks to get outside, then you may need a more powerful hood just to get stuff out. I'm sure your kitchen renovator will probably do the math, but ask anyways.

My hood is mounted on an exterior wall, and I have rigid ducting between the vent cap and the hood.

[coolspot]

Use solid ducting, flexible duct is not as efficient. Any reason you want to use flexible ducting?

If it's because the exhaust holes don't line up - a pro can drill a new hole and patch the old one pretty quick.

[DRF99]

Use solid ducting, flexible duct is not as efficient. Any reason you want to use flexible ducting?

If it's because the exhaust holes don't line up - a pro can drill a new hole and patch the old one pretty quick.

Our contractor put it in last week but hasn't closed anything up yet. There are some obstructions in the way but it may be doable. I agree that solid is better but this is a short run: straight up from the hood, 90 deg turn and then about 4 feet straight and through the exterior wall.

Having cleaned out our dryer ducts (solid) and seen what builds up in there, my main concern is safety.

[cliff]

I agree that solid is better but this is a short run: straight up from the hood, 90 deg turn and then about 4 feet straight and through the exterior wall.

Having cleaned out our dryer ducts (solid) and seen what builds up in there, my main concern is safety.

Exactly, solid is easier to clean (not that it will likely ever be cleaned) but there is less for stuff to catch on the inside with a smooth solid run vs a flexible duct. It also won't sag (resulting in condensation puddles inside the duct where mold can form and requires less support. That and the increased fire resistance is why I went with a solid duct install.

[woof]

(5) A kitchen exhaust duct not equipped with a filter at the inlet end shall be designed and installed so that the entire duct can be cleaned

How exactly do you clean flexible ducting - and without tearing or damaging it sooner or later?