Range Hood venting questions

Crashless

Unfortunately, due to the type of hood we selected and the way it's recirculating kit works, I need to find a way to vent our new range hood outside, and I have a few questions about the requirements of doing so.

The range hood has a rectangular exhaust on the unit, and I was going to use a rectangular vent through the cabinets above it into the attic. From there I would probably switch to a round vent duct (can't remember what size the manual says right now) to go out the back wall of the house rather than the roof.

My questions are these:

Does the ducting have to be double lined, or can I use single lined ducts? What are the clearance consequences of using either material if my attic has blown in insulation? The range is a residential 4 burner gas model.

Can I use an existing attic opening out the back of the house, or do I have to make a new hole? My hope is to avoid going out the roof because there is an old asbestos vent close by and I would prefer to make no more holes in my roof than necessary.

The attic space currently has a couple of different air vents, some decorative brick (6"x12") and one larger (12"x12") metal louvred ones. I would like to hide the vent behind the metal one, is that allowed?

Are there any pitfalls I should be aware of? Anything I'm forgetting?

Thanks so much for your help.

Crashless

Well, I found this post about clearances and single lined vs. doubled lined.

http://www.selfhelpforums.com/showpo...69&postcount=3

It looks like I can use single lined without any need to fire clearance, which is great, but I'm still not sure about venting outside and whether it needs it's own vent opening or not.

Anyone have thoughts on this?

joasis

I have no idea of your location, or applicable code, but the unit should vent outside. I have seen a few attics that had grease stains around the vent pipe, and that is not something I would want in my attic. Of course, I have seen dryers vented into attics and apparently didn't cause any major problems....but.

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Crashless

I guess I should clarify that I'm not intending to vent it into the attic, rather use an existing hole in the attic wall to the outside, instead of sawing a new hole.

I realize venting directly to the attic is a big no-no.

Gencon

You can actually change to round duct right off the hood using a universal boot. Check the specs for sizing and length requirements to see if you can run the distance to the outside wall.

Use only rigid duct and seal it well with foil tape. The duct in the attic must be insulated and vapor barriered as well. They have those slip on sleeves that work well for this.
As for wall termination, you should use a new wall cap that has a backdraft damper in it.

Dont forget to seal up the opening where the duct leaves the attic and enters the house.

brneilly

One other thing you may have or not have considered. If you live in the north where it can get cold...wrap some insulation around the vent in the attic while you're up there. All that warm are from a stove can cause frost to melt on the vent and drip back down through your vent.