Best wall vent cap for range hood exhaust?

4 years ago

I need a 6" wall vent cap for a range hood exhaust. The wall in question does get some pretty intense wind and sideways rain a few times a year. What type will keep cold air, water, and insects out the best? The duct run is going to be pretty short, maybe a foot and a half and then and elbow through the wall. The ducting is 6in. I'm also wondering if it's really best to have rigid ducting. My installer bought the metal flexible ducting, and I was reading that rigid is best. Should I insist on it? Since it's such a small area it may be difficult to get rigid in there. Thanks!

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Comments (4)

Shannon_WI
4 years ago
last modified: 4 years ago
You are correct, the ducting should be rigid. Also, if the walls are open, and you have the opportunity to install new exhaust ducting, it should be 8" in diameter, not 6". People who have 6" ducts have them because they are stuck with them already-behind walls when they moved in, because builders just put in 6" ducts as the easiest thing. If you are installing new ones, they should be 8" in diameter.

You create issues with a 6" duct, mostly a lot of noise as the air is pushed through too small of a space, and less efficiency of the exhaust, because of the smaller duct. See if you can switch to an 8" duct at the same time as you switch to a rigid duct.

I am concerned about your installer. First because AFAIK, flex ducting for an exhaust is against Code everywhere due to fire hazard. Second because he is unable to provide a wall vent cap. These are available at places like Home Depot - they are hooded or lidded, and have a grate at the opening to prevent critters. They are also usually available from the hood manufacturer.

You may want to stop with this contractor, and find another one who knows what he is doing.
Phoebe
Original Author
4 years ago
I don't know that the chimney piece of the hood is large enough to have 8" ducting inside. That would only leave an extremely small portion that would be able to be 8in. I'll double check that, but it's a very short run. Yes, I think you're right about him. unfortunately I don't think I have time to get someone else in here. I have a baby due in less than 4 weeks and our place is a studio type house, so the kitchen is part of everything else. He did buy what he said was the only wall vent cap they had which was rectangular, but the transition piece made it too long to fit. If I have to stick with him, what are some things I should watch to make sure he does? The hood itself actually came with plastic flexible ducting, but said in the manual that rigid metal is best, which struck me as odd.
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I would consider this a low risk worry, but not a negligible risk worry. And there may be an International Building Code or other relevant code violation involved. And I am sure that codes require metal ducting for dryer vents. I don't recall a specific declaration for the termination, but dryer duct fires are a risk that the metal ducting is intended to contain. In commercial settings, the entire exhaust system has to be welded steel. This is to contain grease fires. I haven't read of many kitchen hood vent fires, but that doesn't mean that they can't or don't occur. It would depend on your cooking and the resulting condensation of grease lining the duct. If this is very slight, then the likelihood of propagating a fire to the cap is small. If the plastic cap is not yet installed, _I_ would exchange it for a metal cap. And if you live where snow can accumulate, this cap needs to be high enough that the vent is not blocked. Otherwise, products of gas combustion that aren't healthy might build up when cooking. A blocked vent over an electricity heated stove would only fill the house with cooking effluent, but gas stoves require ventilation for other than aesthetic reasons. kas
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I would doubt that ice dams of any significance would occur for any roof steeper than 4:12, and plausibly for even lower pitches. Not only is the heated area small, but the heat (BTUs per hour times hours of use) exhausted due to cooking is much less than the household heat passing into an attic in cases where ice dams are a problem. I had a major ice dam this winter at the edge of the roof over my kitchen, but the kitchen ceiling was insulated by only a tarp. However, the question of blockage is an interesting one. A sufficiently wet and heavy (yet blowing) snow might pile up in a way that reduces the aperture of the style roof cap that Broan, say, uses for the larger model fans. However, these fans have overhang at the exit (down side) and I doubt that total blockage would occur. So long as some air can pass, then pushing out warm air should clear a larger hole as needed. I won't be able to attest to that until next winter, but I can say that here in southern NH, when in use a Nutone mushroom style exhaust fan with an air exit point about 10-inches above a 5:12 roof, has never been blocked by snow in 20-some years. If a snowstorm were found to be depositing snow that was suspected of being perverse in the blockage sense, then running the fan during the storm should maintain sufficient air clearance to allow the fan to work when the snow hardens up. kas
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I thought about going straight up with it, but I don't have a lot of room due to the angle of the ceiling. Plus, I am going to be using a canopy style hood, so the chase would have to be rather large to be in proportion with the hood, and I'm not sure how that would look. I did think about placing cabinets on top and then a chase above that, but again I am probably too close to the rafters in the attic due to the slope of the ceiling. Consequently, out the wall and into the garage attic seems to be the simplest way to go. Plus, that gets the inline fan away from the house and makes everything more accessible. I don't mind enclosing the vent in drywall to bring it up to code. While the vent needs to be in a soffit, what about the inline blower? It seems like the blower should be left out in the open, with the remainder of the duct enclosed? That said, I can see what you are saying about direct penetrations from the garage into the house are not permitted due to fire concerns. However, would a solid duct running from the kitchen into the garage attic and out the roof fall within that logic? There are no breaks in such a duct run, since the only openings are at the hood itself and wall/roof cap. So as long as the penetration where the duct goes from kitchen to garage is sealed with fire caulking around the duct, how is there an issue? Again, I don't mind enclosing the duct run in a chase if need be, but it seems like overkill....
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Shannon_WI
4 years ago
"the only wall vent cap they had which was rectangular, but the transition piece made it too long to fit. "

I cannot understand what you mean here, but in any case, I did a quick search at Home Depot for "wall vent cap", and got 20+ hits. And stores specializing in HVAC parts will have even more, and an internet search will come up with even more that can be bought online.
Phoebe
Original Author
4 years ago
Since it's rectangular it needed a large piece to transition from round to rectangular. Yes, it appears my local home Depot has round ones in stock. That worries me. What type of tradesman would be best for this job? I have not had good luck with anyone I've hired around here.

Best wall vent cap for range hood exhaust?

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Best wall vent cap for range hood exhaust?

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