Cooker Hood Ducting above Ceiling

[finster]

Hi all,

I am in the process of getting my kitchen refurbed. Currently my cooker is on an interior wall but I want to vent to the outside via some ducting.

As my ceiling is currently down, is it OK to take the ducting across the kitchen to the opposite wall in between the (what will be) ceiling and first floor??? This will be a lot easier than trying to vent to an outside wall (with a RSJ in between).

Is doing this OK, or are there issues because of the electrics for the lights etc are up there?

Thanks in advance...

 

[noseall]

it is wise to keep the ducting as short as possible to help prevent condensation forming as the air in the pipe cools.

it would help if you packed insulation around the pipe. use the rigid rectangular duct and slope it toward the outside wall. this way the condensation will run outside.

 

[finster]

Thanks,

The width of my kitchen is only about 2.5m, so this is how far it would have to go. Is it OK to do this or is the electrician going to blow a fuse (sorry!) when he arrives to do the lights etc around it?

Any advice on what size ducting I will need? I've not got the cooker hood yet, but I'm just thinking I might as well get it all sorted before the plasterer comes and puts another ceiling up!

Thanks in advance...

 

[Richard C]

Marley do a vent kit (B&Q) that contains 99% of what you need – elbows, adaptors & 3M of rectangular ducting. 2 sizes – from memory 100 & 125mm (that’s the round bit) go for the larger size even if you later have to reduce it to fit the cooker hood; it does require an oblong, 1 brick size hole though. I routed the duct from an inside wall between the joists under the f/boards & I really wasn’t looking forward to doing it but it was surprisingly easy! Keep the ducting length to within 3m if you can & support it off the ceiling or it could vibrate. If you’ve no previous experience with extractor hoods, go for one with the largest extract rate you can find, a twin fan unit is best (Bosch do one). The good ones are quiet expensive (mine cost over £700) but the cheap, 150 quid or so units have disappointing performance & can’t cope if your serious about your cooking.

 

[JohnD]

...but if you put your duct and electrical supply in now, you can easily change the hood later when you have £700 to spare

Lots of us common people get by with cheap extractors.

 

[Richard C]

But he's already said he hasn’t bought one yet! I'm not being snobby, just advising to go for the highest extraction rate you can as many of the cheaper units just don’t have enough puff, particularly if you hang them on the end of 3m of ducting!

The one I have now is a bit special I admit but you can get a decent unit for a lot less. If you’re buying new, I can’t see the point of wasting 150 quid on one that is little better than opening a window; just make sure you look at the extract rate which many people don’t!

 

[finster]

Thanks guys, didn't want to cause an argument

When I get around to choosing a hood I'll be sure to pick one that looks like it will expel enough air.

I'll try and install some rectangular ducting at the weekend.

I've found a good link here http://www.marleyplumbinganddrainage.com/v_install_passive.asp

However all of these kits seem to end up going through the wall with a circular hole instead of a rectangular brick-shaped one - is this right?

Also, what kind of connectors do the hoods come with - can I install a "socket" in the ceiling ready for the plasterer to plaster around, and then when I buy the hood in a few weeks time just plug it in????

Many thanks again for all the advice....

 

[noseall]

rectangular ducting has a wide range of bends and converters from rectangle to round etc. you will need to visit a builders yard and see what they've got to suit your scenario.

 

[Richard C]

Thanks guys, didn't want to cause an argument

Don’t worry about it, I won't; havn't got time for 'chips'! You can buy the bits separately but for me the kit had all I needed, it was a bit cheaper than buying the bits separately & may still be a cheaper option even if you only have to add a couple of extra bits. My kit came with a rectangular vent & internal wall plate that fitted over the end of the rectangular duct inside & outside the wall.

Cooker hoods usually come with a 13A plug fitted but can have a bare 3 core cable. You can use either a 13A socket or a 2 pole, switched outlet. Fit the socket/switched outlet in the wall not the ceiling – it must be positioned a min 50mm from the ceiling & any adjacent wall. There is just one fly in the ointment; a kitchen is classed as a special location for electrical work (part P regs. - have a read on the electrics forum) & it’s a bummer! Any electrical work in there must be done by a competent person!!! You have 2 choices; by far the easiest option is to employ a part P spark to do it for you (but make sure he is & you get the paperwork) but if you go DIY you have to notify BC, get them to inspect the hardware & then get a Part P spark to test/certify it for you so you might as well go with option 1 from the start!

 

[finster]

Thanks, I've got a proper sparky doing the electrics and it is all being done under building regs anyway. I actually meant what kind of "ducting socket" I would need if you see what I mean - i.e. after the ceiling is plastered, should there be an end of one of the fittings poking out that my cooker hood ducting plugs into?

I'll nip down to B&Q and see what kind of fittings they have.

Any tips on knocking out the hole in the wall? I think that taking a brick from the outside might be OK but taking a hole out of the blockwork inside might be more tricky....

Thanks again...

 

[Richard C]

Thanks, I've got a proper sparky doing the electrics and it is all being done under building regs anyway. I actually meant what kind of "ducting socket" I would need if you see what I mean - i.e. after the ceiling is plastered, should there be an end of one of the fittings poking out that my cooker hood ducting plugs into?

I'll nip down to B&Q and see what kind of fittings they have.

Any tips on knocking out the hole in the wall? I think that taking a brick from the outside might be OK but taking a hole out of the blockwork inside might be more tricky....

Thanks again...

Sorry; most hood ducts are round so you need the round bit of a rectangular to circular 90 degree elbow poking down through the ceiling; the hood concertina ducting is clamped over the outside of this. The other thing to watch is that the position of the hole can be quiet critical if your thinking of having a ‘chimney’ style hood so you need to keep it on the intended centre line & fairly close the wall.

Line up a complete brick with the preferred position of the duct if you can as it’s easier that trying to shape two half bricks. I drill out the mortar around the brick & drill a line of holes closely together down the centre of the brick; break it in half with a chisel & then wiggle the 2 haves out. I then use a 400mm long masonry drill from the outside to transfer a line of holes through the blockwork; drill some more holes through the centre to make it easier to break out; chisel this out & dress the edges straight until the duct is a snug fit. Check there are no lintels or anything else behind the blockwork that you could damage before you start.

 

[finster]

Thanks Richard,

I called at B&Q tonight and spent a good while trying to find all the bits that connect together...

I saw the kits that you mentioned, but although they were labelled as 3 metres, this consisted of 2 metres of rectangular duct and 1 metre of circular. They didn't have any rectangular duct in the same size sold separately.

Due to limitations of fittings that they stocked in the end I went for the smaller rectangular pipe. So I've got 3 sections of duct, 2 connectors, a ventilation grille, a couple of clips and a flat to round 90 degree connector.

I'm still a bit confused how the whole thing should terminate at the cooker end though. The 90 degree connector will be too high up to poke through the ceiling, should I just connect some round flexible hose and let it dangle through and then worry about connecting it to the hood when I get it....

Cheers.

 

[Richard C]

I'm still a bit confused how the whole thing should terminate at the cooker end though. The 90 degree connector will be too high up to poke through the ceiling, should I just connect some round flexible hose and let it dangle through and then worry about connecting it to the hood when I get it....

Cheers.

I would advise you get a section of circular rigid duct to poke through the ceiling; you will then be able to clamp the flexible duct directly onto this. My kit included a short circular duct section that fitted directly into the 90 degreed bend & it projected through the ceiling around 40mm, more than enough to clamp the hood flexible onto.

 

[finster]

Thanks Richard,

All done and ready for plastering tomorrow. Cutting a hole through the wall was a bit of a pain but I got there in the end.... The only rigid cylindrical tube I could find was some telescopic stuff (basically one tube inside another), but I think it will do the trick.

Thanks again...