Hob Extractor Re-Ducting

DrSeuss

Hi, Can anyone give any advice, recommendations etc to the placement of ducting for an extractor fan.

We are renovating the kitchen. The current kitchen extractor ducting enters the ceiling and runs parallel across the kitchen to an outlet on the roof of an extension.

the new kitchen and extractor will be on an internal wall. Currently we will be installing a recirculating hood, but I would like to convert this to a vented hood.

what’s the best way to re-route the ducting to the current external vent?

anyone recommend anyone that can do this?

thanks

cnocbui

I would think your best option is a ceiling mounted extractor in the new position, not a wall mounted one, then it's a relatively simple matter to connect the ceilng space duct to the new extractor.

When I once installed a wall mounted extractor, I bored a 100mm hole through the external concrete cavity wall to make it external venting and not recirculating. I don't see how you mount to an internal wall and make it externally venting unless you do something fugly on the far side of the internal wall or it has some optin to run a duct vertically into the ceiling.

DrSeuss

thanks for the advice. Im concerned as I now have to go across the ceiling approx 2m to attach to the current ducting in the ceiling. Not sure if I’ll be able to cross the joists in the ceiling.

where to cut the ceiling is also going to be an issue.

anyone done this before or recommend who to get to do it?

DrSeuss

Does anyone know if there is a gap between the joists and plasterboard either above or below that ducting will fit through?

cnocbui

https://www.boards.ie/discussion/comment/120405253#Comment_120405253

Assuming you have a normal ceiling cavity, you'd have the plasterboard ceiling attached to the joists, insulation between the joists and than an empty void between the insulation/joists and the underside of the roof. When I did my ceiling mounted extractor, I just connected 120mm flexible ducting to the outlet of the extractor in the ceiling and then ran it to where i had it vent externally, so the ducting just lies on top of the joists and insulation like a fat silver snake. It's very light.

DrSeuss

https://www.boards.ie/discussion/comment/120406369#Comment_120406369

Thank you for this.

My issue is that the current external vent is out via the roof of an extension. So the current duct is run through the ceiling in the kitchen and floor of the upstairs.

I doubt there is a gap to run new ducting and join up to the current external vent.

10-10-20

If like in my kitchen you can't get the extractor ducting to route directly and you don't want to go down the route of boxing it in, then you may need to install a good quality recirculating hood and then also fit an extractor off the old ducting in addition to it. That's what I did and I installed a humidistat to kick the fan off automatically in case it wasn't turned on manually.

DrSeuss

https://www.boards.ie/discussion/comment/120409806#Comment_120409806

This is another option, thanks.

Why couldnt you fit the ducting directly?

Where did you fit the extractor? On the ceiling? I could do this in the middle of the kitchen and fit a humidistat.

10-10-20

The joists run the length of my kitchen with the ends into internal walls on both sides.

I fitted the extractor into an existing 100mm vent and put a flap on the outside. It's undersized for a kitchen (should be 150mm) - but that's a job for another day.

DrSeuss

https://www.boards.ie/discussion/comment/120411190#Comment_120411190

I may have to use this option. I could fit the extractor onto the ceiling and aatch it to the exisiting ducting that runs the lenght of the kitchen.

My hope was that I could run a new PVC flat duct across to meet the existing.(as in my terrible example)

10-10-20

Don't bother with that flat-channel stuff, it's not going to work for the air-volume that a kitchen needs. Plus the static pressure which a standard fan generates will overload the flat-channel anyway. It's a pig when houses aren't designed to take proper extraction fans.

DrSeuss

Is there anyway to vent across to meet the current ducting? Or are the joists limiting this

10-10-20

Cutting or making holes that large in joists just is not possible. If you do want to join up to the existing duct then you need to look at running it under the ceiling and using cladding/coving to conceal it.