hood fan vent delemma

[phil]

my hood fan had started leaking prior to this stage of roofing ( over the kitchen)
when I stripped the roof and removed the tin box vent thing, I found it had a piece of 3x10 square vent protruding the shiplap. the edges were bent flat against the shiplap and nailed down.

I bent the tin back and resheeted the area with plywood over the shiplap , bent the tin back down and nailed it to the plywood.

then I looked at the plastic vent cover I had purchased. It has a ridge that surrounds a round hole so it looks like the vent cover wants a 6 inch pipe to be sticking out of the roof, not a 3x10 square shape.

So, Ive been pondering the age old question of how to make a square peg fit in a round hole!

I spoke to a sheet metal guy. he said it was done wrong and that the vent pipe should be round not square and it should protrude about an inch or so. what I uncovered was a mickey mouse mess evidently. he said don't leave it like that, it'll leak.

It's a bit awkward to access because the area has had the roof raised up a bit and so there is this dead space between the two roofs. I can access the underside of the first roof so maybe I just have to cut my way through into the area. now my aim is to remove the hunk of square vent pipe and then I should have a straight run of 6 inch round that protrudes the roof..

.. another learning experience I guess..
Phil

[nhguy]

You'll certainly have more options for a vent cover in 6 inch.

[phil]

I had a look and noted that I did a nice job of fitting the parts inside the cabinetry. it looks like a pain to try to get a round pipe down there. Ill have to use a jig saw or somethign to cut the top of my cabinet to take a round pipe then maybe make a cover to fix it so it doesnt' look like a mess.
of course there is a way, perhaps I could put a 3 1/4 x10 to 6 inch adapter down inside the 3 1/4 x10 and sort of stuff it in further than they are normally meant to.
regular vents often dont have any pipe connected and they don't leak, its just a hole with the cover over it. I'm not too concerned about the air being disturbed by the adapters, I just dont want it to leak and I guess it bugs me it isnt' done correctly.
when I built the cabinets I had no idea it was done wrong.
I dont think 3 1/4" x 10" square pipes usually come through the roof so I dont seem to see covers for that, maybe ones that are for going through walls, dryer vents and such. now I have my plywood over the shiplap and the membrane over it I don't really want to enter from the roof, and cutting into that triangular space through the attic looks messy too. I'm trying to decide what to do, try to yank the square one out and replace with a round pipe, or adapt it somehow.

[phil]

I went to home depot and looked at what they have. some are sort of two layers and I thought well maybe I just need a flange that fits. i could marry that with the old metal vent.

I did a little tinbashing so I've got something made up. its a piece of tin with a hole 4 1/4 x 8 , the vent is 10" wide and the vent cover indented part is 8" wide, bu the vent's flange is about 4" all around so it's about 16 x 17 , it'll cover the hole.

I folded up the edges added a 2" strip that protrudes the hole about an inch either side. I figured I could solder all the parts together or use sheet metal screws then pipe sealant or something. that gives me a lip so water couuldn't drip down into the vent and something that kind of fits the pipe

It'll have to have some "ears" to direct the air from the wider duct through the opening. I need some taper inside the sides of the duct near the flange because the vent hole isn't as wide as the duct. That will make it smoother for the air going through.

I loose 4 - 5 square inches of area and a 4 1/4x 10 vent is 42.5 square inches.

It'll work but it isn't' really correct and I dont know whether to try to rip whats there apart and get the 6" pipe where it should be or do my kludge with the adapter plate. I'd rather yank that square duct out and put in a 6" pipe but it's an awkward job. I wanted to move ahead with roofing not start tearing my upper cabinet apart but I guess I am thinking in two directions. wiht a plan A and a plan B

the metal vent cover makes a bit of noise when crows land on it and stuff, and rain, I had bees in it. the plastic ones, although I dont like using plastic are at least quiet and won't rust. I guess they last as long as the roofing will anyway. I got some paint that matches the others if I go with the tin one. i wonder if the bees might like the tin vent better than the plastic, maybe they cant' stick their nest so well to plastic. the 1/4 inch screen didn't stop the workers from building in there, but maybe it would stop a queen from entering.

once the vent covers are installed it would be really hard to get to a bees nest, you'd have to muck with the roofing. I guess you could put raid or something through the hood fan. It looked like they'd go building and it was active, but then when I ran the fan it would blow them out while it was on. since I had a roof leak I ran it long periods so I probably unknowingly extracted most of them

[phil]

I ended up manufacturing a piece of metal with a hole in it and a flange that sticks up about an inch and down into the square vent. it'll stop rain from running down if it ever gets there. i attached that to the plywood, then I painted and installed the original tin vent with it's flashing so it got shingled in with the roofing.
replacing the square vent with a round one seemed problematic because they had used that square pipe in a weird way , by sort of doubling it up and sistering the pipe to avoid some beams. If I had replaced it with a round pipe it would have come through into the upper cabinet in a weird way and used up what space is there with adapters to shift the thing over.
the opening is a bit reduced from 6" so it wont flow as well. it has some restriction due to reduced diameter but I decided it's not going to be a problem worth days of fretting over.

[Mick_VT]

IMO the rectangular vent pipe is not "wrong", just tends to be used in tight spaces. If it were indeed wrong you would not be able to buy the right vent caps and outlets for it

Coincidentally I had to use rectangular ductwork for my kitchen hood in order to run it above the ceiling and out as my 1860 house doesn't use modern sized joists (they are 8"x 4" would you believe?) and there was no way the recommended 8" round pipe was making it through

[phil]

turned out my square vent was 3 x 10 1/4. I didnt find any roof vents that took square pipe other than dryer vents intended to go on the wall.

sometimes the running around finding things takes more time than finding a solution but I was able to make up a box that stood proud 1/2" or so above the roof deck so water shouldnt; find any way to run down, and I used the old metal cover. it was a little smaller than I would have liked but oh well it should be ok now. the metal cover had flashing so it shoudl work fine.

the other plastic roof vents I put in for ventilation didnt have anything other than the way they shingle in with the roofing and they don't seem to leak.

I just have to find some flashings now to fit the top of the pipes that stick up because the pipe runs up higher than the lead flashing. Evidently there is a cap or counterflashing for this but the issue is that most retailers have now gone to a tin plate with a rubber bushing and lead parts are a bit hard to obtain.

the "correct" lead cap has a hole in it but sort of a flange where it can be rolled into the opening of the pipe and cover the other lead that is wrapped around the pipe. I see some houses have a thing that looks like a space ship, maybe I could get artsy with them. If I just wrapped butyl tape around the lead and the pipe it might work and that would be simple

If I can't find lead parts I can probably use copper pipe and solder a flat top on that with a hole in it so that I can form it around the pipe.

I just found some brass railings on craigslist, i might be able to use a chunk of that for the smaller ones. they come with some mounting fixtures and round brass pipe , it looks old. Im unsure of the dimensions. I thought I might be able to use some of it to make a log stop for the fireplace otherwise maybe a nice brass railing. I have a set of stairs to my bedroom It has a railing but i was thinking one on the side of the wall might be ok to add a bit of safety. The boss wants a coat rack so I could make one from brass, I have a bunch of old brass coathooks.
its $50 for a few chunks of old brass pipe. I figure its probably close to the scrap value so not too much to risk there i have all sorts of ideas for it. looks like about 4, 8 foot sections. brass is kind of fun to work with.
I can always take up pole dancing