Need to vent range hood

[FITO]

Not sure if anyone in the HVAC business could help but I need to vent my range hood through the roof.
Previous home owner/builder just vented hood into attic. I think its rated at 1200 cfm and has a 8" vent. Can I taper this to 4" and go through the roof or should I stay at 8"?
Also, what is the best type of cap, I get all the seasons.

Thanks for any input

 

[Milton Shaw]

You need to keep it 8" or you will cut the air flow to nothing. A vent cover should be available from a roofing supplier or from a hvac supplier. I have seen people who had reduced the size of the pipe and you might as well not have a vent when you do that.

 

[Falcon67]

DO not reduce and don't bother looking in the big box stores for the parts either. I'd use (and will - have same issue) a low profile cap like pictured here:
http://www.homedepot.com/buy/bath/bath-fans/broan/roof-vent-kit-66750.html
That is a 4" kit, for a performance 8" hood you need 8" all the way. You'll have to special order all if it, if my experience holds. I have a big vent we were going to use in a kitchen remodel that is now surplus. Glad I didn't buy the vent parts too.

 

[FITO]

I looked in the box stores for a 8" flange with no luck and thats how I came up with reducing. I like the look of the Broan, I'll try and get one online, thanks for the link. When we bought the place there was a film of grease on the inside of the bathroom fan light lenses. That thing moves some serious air on high.