Advise on range hood vent

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jaymz

1133 posts

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#64043 6-Jul-2010 20:43

Hi guys,

Not sure if anyone can help, but who knows!

Currently we have a range hood which vents directly into the roof cavity. I would like to vent this externally so that the moisture from cooking doesn't stay in the roof.
I have drawn a basic diagram of the current setup here:
https://cdn.geekzone.co.nz/imagessubs/blog51899af11d0ab5fdf29228a2a27ca382.jpg

What I would like to do is run the vent to the top of the underside of the eve of the house. However the vent into the roof is pointing vertical.

Does anyone one know if I can put a 90degree angle on it (or run a section of bendy ducting on a gentler angle)?

Proposed diagram is here:
https://cdn.geekzone.co.nz/imagessubs/bloge9145413b52b556ba83f97c775072b4b.jpg

Let me know what your thoughts are on this.

Thanks

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#348559 6-Jul-2010 21:28

What about a little pipe chimney with one of those chinaman hat cover on it. Then you can vent straight up. I'm not a builder at all but venting downwards doesn't sound great. Not sure of the long term effects on the eaves. We had an extractor fan put in the bathroom and had the chimney put in, looks ok.

https://cdn.geekzone.co.nz/imagessubs/blog77f94d360f7571864cd4ad2115fb4fc1.jpg

Regs

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Snowflake

#348564 6-Jul-2010 21:41

as long as the motor in the rangehood is strong enough to push the air out there shouldnt be any problems doing that

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Johnk

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#348566 6-Jul-2010 21:43

You can easily get flexible ducting at either J.A. Russels or Ideal electrical. would do exactly like like your proposed drawing.

jaymz

1133 posts

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#348586 6-Jul-2010 22:26

lurker: What about a little pipe chimney with one of those chinaman hat cover on it. Then you can vent straight up. I'm not a builder at all but venting downwards doesn't sound great. Not sure of the long term effects on the eaves. We had an extractor fan put in the bathroom and had the chimney put in, looks ok.

https://cdn.geekzone.co.nz/imagessubs/blog77f94d360f7571864cd4ad2115fb4fc1.jpg

Yeah, Ideally that would be what I would do. Unfotunatly we have a concrete tile roof and am unsure on how I would cut a hole in it to do that.

Our bathroom vent exits the house in a similar fashion to what I want to do and that seems to work fine.

nickb800

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#348591 6-Jul-2010 22:43

We have the same for our bathroom fan too so cannot see why you couldnt for kitchen.
Opening the roof is easy but messy and exposes the possiblity of leaks so I wouldnt bother.

Just make sure the duct is sealed well, especially near the outlet, otherwise it may leak condensation and rot the under eaves board as happened in our flat

nickd

447 posts

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#348594 6-Jul-2010 22:53

Dads a builder, use bendy ducting, it's exactly what we have done in our house, works sweet.

Jaxson

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#348653 7-Jul-2010 09:50

You'll need an adaptor to convert the square shape to a round one you can attach ducting too. No reason why you can't do either. Straight up and out presents less friction so will be more efficient. If you use 'bendy' ducting then pull it fairly tight to reduce drag in the duct.

You'll need in total: duct shape adaptor, ducting, soffit grill.

Make sure your outlet is located away from windows and doors if possible. If you have to squash the ducting too much to fit to the soffit cavity then this will further reduce the efficiency of the rangehood. It's a lot cheaper though than a roof penetration, especially on tiles.

Air can only flow out the rangehood as fast as it can enter and be replaced in the the kitchen room, so open a window on the other side of the room/house etc if you really need good flow.

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jaymz

1133 posts

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#348660 7-Jul-2010 10:09

Jaxson: You'll need an adaptor to convert the square shape to a round one you can attach ducting too. No reason why you can't do either. Straight up and out presents less friction so will be more efficient. If you use 'bendy' ducting then pull it fairly tight to reduce drag in the duct.

You'll need in total: duct shape adaptor, ducting, soffit grill.

Make sure your outlet is located away from windows and doors if possible. If you have to squash the ducting too much to fit to the soffit cavity then this will further reduce the efficiency of the rangehood. It's a lot cheaper though than a roof penetration, especially on tiles.

Air can only flow out the rangehood as fast as it can enter and be replaced in the the kitchen room, so open a window on the other side of the room/house etc if you really need good flow.

Yeah I noticed that there looks like there should be an adapter for it but I can find it in the house anywhere (people who installed it may have thrown it away)

Thanks for the advice, that has given me all I need! I will have a hunt around for an adapter and ducting in the next few days.

Thanks guys

1gkar

722 posts

Ultimate Geek

#348850 7-Jul-2010 20:53

One thing to be aware of is to use aluminium flexible ducting, instead of the plastic variety. This is a requirement under the building code. If it is not used, then you could find issues if the insurance company gets involved if any problems arise.

Also, make certain the rangehood's fan is strong enough, which it should be if it is a named brand.

To answer your query about how to flash a solid duct penetration through the tiles, you can buy a tile flashing by a manufacturer called Dektite. This has a rubber concial flashing, which you cut to the right diameter of the flue, & is surrounded by an artificial lead product for bossing down (beating to the tile's profile). A plumbing merchants may be able to assist here.

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jaymz

1133 posts

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#348940 8-Jul-2010 07:53

Sorry probably should have mentioned the brand, its a Tilt-A-Hood Classique and from the sound and feel of air going into it the unit should have plenty of guts to force the air through.

With the tile roofing, I am not going to try put it through it as it looks like too much hard work, I would have to remove the tiles around the vent in order to cut the hole, plus I don't have any tools to cut a nice clean hole through concrete tiles. This is the reason why I will put it through the eve.

Thanks for the heads up on the ducting, I will make sure it is the aluminium variety (I have never seen plain plastic ones before though?)

1gkar

722 posts

Ultimate Geek

#349610 9-Jul-2010 18:05

Meant to get back as I remembered you can get all-in-1 kits. they comprise a section of ali flexi-duct, a length of solid plastic flue, for through the roof, a similar material u-bend for the terminal, & a flashing. I am pretty sure I have only ever installed these onto longrun metal roofing, so not sure if they do a tile roof version. The metal roof product would not work on tiles as the flashing would be of the incorrect type.

I believe I purchased these through Chesters Plumbing mercahnts. Can't remember the manufacturer, though.

Semaj

23 posts

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#349618 9-Jul-2010 18:35

Hi jamz, check out - www.robinhood.co.nz
Have a look at their ducting hints.
With the concertina type flexible tubing
there will be roughly a 28% reduction in
air flow due to the turbulence.
Cheers.

Handle9

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#349638 9-Jul-2010 19:10

Just go to Bunnings/Mitre 10/ insert favourite hardware store here. Flexi alumium ducting costs about $20 for 3m and a grille is about the same. I've just done this for my rangehood and it works very well. Yes there is a bit of a reduction in air flow but you'll get most of the air out (I've just bought a new rangehood that goes like hell anyway). The main issues you'll have are making sure you get a good seal around your joins. Make sure you use heaps of duct tape and test it while you're still in the ceiling so if you need to put more tape on you can do it.

The through roof kits are great but cost around $200.

If you have a look at the bigger hardware stores they'll usually have converters from rectangular to round ducting. They're usually around their kitchen departments.

jaymz

1133 posts

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#349683 9-Jul-2010 22:09

Semaj: Hi jamz, check out - www.robinhood.co.nz
Have a look at their ducting hints.
With the concertina type flexible tubing
there will be roughly a 28% reduction in
air flow due to the turbulence.
Cheers.

Sweet, thanks dude. That site is quite good, explains things nicely.
Wonder where you can get the UNIDuct Kits from, maybe bunnings will have them?

Thanks for all your advice guys, I am off to Bunnings tomorrow to get a few things I think I will need:

-Ducting
-Adapter from square to round
-Outlet grill
-Heat resistant tape

Hopefully the install will go fine.

jaymz

1133 posts

Uber Geek

#350401 12-Jul-2010 20:42

Right, so the weekend was a fruitless effort!

Bunnings did not have the right size part (perfect lenght, but too narrow) and Mitre 10 Mega was the same. J A Russell didn't have anything either - At that point I gave up.

Bunnings will call tomorrow with advise from their supplier, hopefully they find something.

In the meantime, anyone know where I can find a rectangle to circle adapter for a 285mm by 110mm rectangle?

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