How do I install an exhaust vent for a chimney-style range hood?

17 years ago

First off, I don't know anything about installing things like this, so give me some slack. :-)

I have recently remodeled my kitchen and now need to install a range hood for the new cooktop. I will be getting a chimney-style wall mounted hood that extends straight up into the attic. It will be installed in a place with no previous ducting of any kind. The old kitchen had a recirculating, under the cabinet-type thing. What is the proper kind of vent for this application? If possible, I would like to go straight up into the attic and then through the roof. I know I will need 6" rigid metal ducting, but am not sure about the part that goes on the roof. Any help?

Thanks,

Neil

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Comments (3)

snoonyb
17 years ago
How do you know you need 6" round metal duct?
You size the venting appliance per the cooking appliance MFG. recomendations.

The "chimney" is usually an enclosure with the vent pipe inside. You install the vent tubing from 3" below the ceiling thru the roof, terminating with a "T" top roof flashing.
neilometer
Original Author
17 years ago
snoonyb,

I was basing my need for 6" ducting on the specs for the hoods that I'm looking at. They all spec a 6" duct size.

Can you tell me a little more about "T" top roof flashing?

Thanks,
Neil
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Thanks, all, this is useful: cawaps: full-width duct cover, that'd be perfect! I imagined my contractor rigging something, but of course it makes sense they make hoods that come with such a cover built in. huango and palimpest: the straight regular chimney does look nice, and if space/construction allows that'd be great. In our case it's not a full reno, though just the hood, so if breaking into the ceiling adds much $$$ that might not be worth it. But if it isn't a big deal for the contractor, we'll do it bellsmom: I get what you're saying, and yes, that would work too if for whatever reason a hood with full-width cover isn't a good option. And it would give us a bit of storage, too. Problem #2 that just ocurred to me is the side wall exhaust would come out immediately under our retractable deck awning. Hot exhaust under vinyl (or whatever it is) might not be a good idea, or at the least it could trap the smoke right there by the patio door. Hmm. If our fridge and stove were swapped this could work. In the fridge location, the stove would back to an exterior wall with no utilities or external obstructions, and the little over-fridge cabinet would be the right height for an u/c hood. Would have to remove the over-stove cabinet to make room for fridge, but no big loss. But, this would mean running a new gas line and a new water line (ice maker), and leave the stove closer to the sink than we'd like. Oh, how quickly it all snowballs!
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@opaone: your numbers, while still higher than my estimates, are at least within an order of magnitude, which in this business probably is reasonable correlation. I agree that this could rise to a significant concern with 10 people really cranking away in a poorly ventilated room. So we're on the same wavelength. @spurpura: you are correct in that I've not invested in air quality monitoring devices or hired PhD's to test my house. But my calculations are grounded in simple physics. The only assumption I have made is in the estimate of CO2 production during exercise, and that was from an academic sports physiology laboratory, authored by a PhD and published in a peer-reviewed journal. If you have figures showing that CO2 production during exercise is roughly 10 times higher than my estimate (which is what would be needed to support your observations), I'll await the citation. There are really only three possible scenarios: You are measuring local concentrations of CO2, presumably close to where you are exhaling. Your PhD consultants and their equipment are wrong. There's an exogenous unidentified source of CO2 infiltrating your exercise room. Enough of that dead end discussion. But...as to your original question, I think you're on the right track. As noted upthread, our 1200 cfm hood runs through a straight run of 10" duct, about 25' upwards, with an attic-mounted Fantech LD10 silencer and FKD10XL blower. It measures 60db (LCS weighted, ear level, roughly 4' from baffles) on high. So we hit the mark you are shooting for and I expect your setup will too. Good luck!
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sierraeast
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If your hood is on an outside wall, your not going to want to protrude through the roof too close to an overhang, especially if you are in cold country with ice dam concerns.You would have to elbow up to a higher location.In our area,a fire stop is required where the ducting enters the cieling/attic with any framing required to be 2" away from the duct.A fire stop is a sheet metal jack that accepts the ducting in the center.The fire stop is attached in your attic to cieling joists or blocking or both.The fire stop isn't so much for heat,as hoods aren't high heat,but are required to slow fire through penetrations.Your roof sheathing should be cut 2" larger than the ducting as well. The roof jack will easily cover that. A t-top roof jack is simply a jack that has a horizontal "hood" that keeps water out of the jack/ducting. You are going to want to study how other vents on your roof were flashed as well concerning your roofing, as an improper flashed jack is a guaranteed leak.If you use foil tape on the seams of your ducting,(my choice), make sure it is rated for heat.Good luck on your project! You might want to check in with your local yocals for venting requirements in your area. That's what they are there for and is a safer bet.

How do I install an exhaust vent for a chimney-style range hood?

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snoonyb

neilometer
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How do I install an exhaust vent for a chimney-style range hood?

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snoonyb

neilometerOriginal Author

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neilometer
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