Awkward kitchen extractor - will this work?

[Tim Cognito]

I really want to externally vent our island cooker hood but the routing and vent location is a bit awkward. I've not done anything like this before so would really appreciate some feedback on the plan of attack.

Starting from the cooker hood, I would run along the left facing wall which I assume has an RSJ in it from where the kitchen has been opened out. Then through the far wall. I would box in with mdf and paint. Obviously it will be visible but once painted and given it's on the ceiling I don't think it will be that offensive?


This would then come out where the arrow is and then turn 90 degrees to go through the outside wall.


Outside is also cluttered. The cross is approx where it would exit which should be 300mm away from the boiler flue.


Any massive flaws i've not thought of?

[allegro]

what's the step down in the ceiling? is it an extension with a pitched roof?

[Simpo Two]

Try to keep bends to a minimum. Can you go straight out from the back of the unit to the outside wall?

Either way for best results have a 150mm round duct. Paint it ceiling colour and you won't really notice it.

NB Any chance you can run it in the ceiling between the joists?

[Tim Cognito]

allegro said:

what's the step down in the ceiling? is it an extension with a pitched roof?

Yes extension with a pitched roof and vaulted ceiling, and at the other end is (almost) all glass so no way out that direction really.

[Tim Cognito]

Simpo Two said:

Try to keep bends to a minimum. Can you go straight out from the back of the unit to the outside wall?

Either way for best results have a 150mm round duct. Paint it ceiling colour and you won't really notice it.

NB Any chance you can run it in the ceiling between the joists?

There would only be 2 x 90 degree bends in the pipework with that routing.

Not sure which way the joists run in the bedroom above. I know the joists downstairs run the wrong way, I assume upstairs would be the same?

[dickymint]

From memory of boiler flue outlets it's 300mm minimum horizontally but 1500mm vertically - not sure if self closing 'flaps' would negate that rule? As regards the ducting I'd say yes 2 x 90 elbows would be OK but use spiral/solid duct not flexi.

PS. the flue distance wouldn't bother me but I'm not allowed to say that

[Tim Cognito]

dickymint said:

From memory of boiler flue outlets it's 300mm minimum horizontally but 1500mm vertically - not sure if self closing 'flaps' would negate that rule? As regards the ducting I'd say yes 2 x 90 elbows would be OK but use spiral/solid duct not flexi.

PS. the flue distance wouldn't bother me but I'm not allowed to say that

According to chat gpt for condensing fan assisted boilers it's 300 mm vertically.

[dickymint]

Tim Cognito said:

dickymint said:

From memory of boiler flue outlets it's 300mm minimum horizontally but 1500mm vertically - not sure if self closing 'flaps' would negate that rule? As regards the ducting I'd say yes 2 x 90 elbows would be OK but use spiral/solid duct not flexi.

PS. the flue distance wouldn't bother me but I'm not allowed to say that

According to chat gpt for condensing fan assisted boilers it's 300 mm vertically.

Just had a look and you appear to be correct. It's a long time since since i was up on the regs. I have a memory of vertical distance being a fair bit more than the horizontal. At the end of the day the manufacturers installation instructions of your boiler takes precedence over the regs

[dobly]

Island cooker hoods are usually installed so that the ductwork is above the ceiling - either vertical in a single storey kitchen, or horizontal-ish where there is another floor above. Either way, the ductwork is not in the kitchen. I would be trying to find another route out rather than putting boxing on the visible side of the ceiling.
Whoever installed a recirculating island hood in the first instance was going for style over substance/performance - not a good sign.

Edited by dobly on Friday 27th February 04:43

Edited by dobly on Friday 27th February 04:44

[LooneyTunes]

Tim Cognito said:

Simpo Two said:

Try to keep bends to a minimum. Can you go straight out from the back of the unit to the outside wall?

Either way for best results have a 150mm round duct. Paint it ceiling colour and you won't really notice it.

NB Any chance you can run it in the ceiling between the joists?

There would only be 2 x 90 degree bends in the pipework with that routing.

Not sure which way the joists run in the bedroom above. I know the joists downstairs run the wrong way, I assume upstairs would be the same?

Can’t quite picture where the unit is vs the cross on the wall you sketch an overhead plan view?

From what you’ve drawn, going out the side involves 3 x 90 degree bends (there would be one at the top of the unit’s vertical column). That’s quite a lot of bends/resistance.

I’ve converted several from recirc to external venting, and straight out the back is by far the simplest if it is on an external wall.

Things to watch out for:
1) Core drill bit sizing relates to the size of hole they make. Ducting size relates to the internal diameter of the duct. You aren’t getting a 150mm duct through a 150mm hole… seeing builder get this one wrong is why I now own a 165mm capable core drill and bit.
2) Hire or buy a proper core drill machine. Yes you can use a clutchless drill and risk the torque when the bit catches or bang it in a SDS and risk burning the clutch out but it’s far from ideal.
3) Drill your pilot hole using a long bit from the inside. Core drill from the outside (much dust will be generated).
4) 90deg bends are very bad for airflow. Better off with smooth curves if you can. You can achieve these with expanding metal ducting.
5) Check all your bend radii, including those inside the unit, before you drill.
6) Flappy vent covers on the outside also really harm your airflow (and can be noisy).

If you end up needing to box in ducting, use plasterboard and have it skimmed. It’ll be far better that painting MDF.

Don’t forget that you can also get flat ducting (and connectors that go from round to flat) which can make hiding it easier. Using some myself on a new bathroom at home because I can’t get round duct past pipe work in the ceiling void).

[Quattr04.]

That’s going to look crap

Get rid of it completely and get one of those hobs with the extractor in the hob, patch the holes in the ceiling and job done

[037]

Use rigid ducting if you decide to go ahead with it.

[Chumley.mouse]

Quattr04. said:

That s going to look crap

Get rid of it completely and get one of those hobs with the extractor in the hob, patch the holes in the ceiling and job done

He will still need to vent the extractor if it’s in the hob .

[Tim Cognito]

Quattr04. said:

That s going to look crap

Get rid of it completely and get one of those hobs with the extractor in the hob, patch the holes in the ceiling and job done

I would like to do away with the ceiling mounted hood entirely as it would open up the space really nicely but.

1. I don't want to lose all the storage in the island
2. Downdraft extractors don't have the best reputation at extracting
3. Venting externally from below the floor is going to be a massive hassle if even possible

[dickymint]

Tim Cognito said:

Quattr04. said:

That s going to look crap

Get rid of it completely and get one of those hobs with the extractor in the hob, patch the holes in the ceiling and job done

I would like to do away with the ceiling mounted hood entirely as it would open up the space really nicely but.

1. I don't want to lose all the storage in the island
2. Downdraft extractors don't have the best reputation at extracting
3. Venting externally from below the floor is going to be a massive hassle if even possible

Downdraft hobs can be recirculating or ducted. Nothing wrong with recirculating BUT most people rarely clean the filters often enough.

[Watcher of the skies]

You want to have a word with whoever is drawing willies on your ceiling.

[AndyTR]

We had a bora in the kitchen at our last house and it was much better than the over cooker hood it replaced. I'd recommend finding a couple of kitchen places that have downdraft hobs and go for a demo. Also with most you only lose the top drawer if recirculating. We're planning a new kitchen in the new house at the moment and we'll be going induction and downdraft again.

[Tim Cognito]

Thanks for all the replies so far. I will get more photos and a floor plan and add later this evening.

[Simpo Two]

Tim Cognito said:

Not sure which way the joists run in the bedroom above. I know the joists downstairs run the wrong way, I assume upstairs would be the same?

If you can see which way the floorboards run, they go at right angles to those. Not sure if you'd get 150mm round ducting in but the biggest rectangular ducting that would fit would be invisible and still work OK.

Re the comment about a 150mm core drill not being big enough for a 150mm duct, when fitting mine I drilled a ring of small holes through the wall and then bashed out the middle bit.

[eps]

If it were me I would just add an external extractor, which is separate to the hob one. This would keep things a lot simpler, which in my mind is always a good thing and usually cheaper and better!!

Then think about what you want to do with the hob one, as in keep it, change it or even remove it. All the hob one is doing is sucking it up and pushing it out at ceiling height right now.