Venting kitchen extractor fan outside

slicendice

Hi everyone
As a recent homeowner I am starting to come to terms with the fact that I will never have disposable income again...ever! The latest thing to drain my already beleaguered finances is a kitchen refit and one of the issues I'm unsure about is where/how to vent the extractor fan.

After conferring with the guy I bought the house off, it seems the current extractor fan vents into the old chimney in the corner of the kitchen but as I'd rather not do that (all sort of potential hazards!), I want to vent it outside.

The kitchen isn't big (3m x 2.5m) but the hob/extractor is against an internal wall so the ducting would have to go from there to an external wall. I've read a few reports that state that ducting for kitchen extractor fans shouldn't exceed 5m, dropping by 1.2m for every 90 degree bend. Given I'd need one 90 degree bend, that allows me up to 3.8m which I think should be just about OK. However, I have read also that you shouldn't duct more than 3m as kitchen extractors aren't powerful enough.

I know it's possible to set up extractors to recirculate and use carbon filters etc, but my g/f's parents used to have a recirculating extractor fan and had all kinds of problems with mold and damp...until they switched to an external extractor and all the issues went away.

So I'm wondering has anyone ducted this sort of distance from a kitchen extractor (i.e. >3m)? Was it OK? Any pitfalls?

Thanks...

Gloomendoom

If you want to run longer lengths without restricting the flow to useless levels, you need to increase the size of the ducting.

I've never tried it, but you could also add an extra fan into the system to boost the flow with standard ducting.

FreeBear

slicendice wrote: »

So I'm wondering has anyone ducted this sort of distance from a kitchen extractor (i.e. >3m)? Was it OK? Any pitfalls?

I fitted just shy of 3m of rigid ducting for my extractor along with ~500mm of flexi. The flexi comes out of the extractor in to a 90° round to rectangular adapter (204x60mm). The rigid ducting is hidden between the ceiling joists and vents through an "air brick" installed in the external barge board.

It works quite well, isn't too noisy, and the external vent is very discrete.

As long as you can use rigid ducting for the bulk of the installation, going over 3m shouldn't be a problem.

elliot341

You can see the rigid ducting I used in my kitchen running above the wall units

slicendice

FreeBear wrote: »

I fitted just shy of 3m of rigid ducting for my extractor along with ~500mm of flexi. The flexi comes out of the extractor in to a 90° round to rectangular adapter (204x60mm). The rigid ducting is hidden between the ceiling joists and vents through an "air brick" installed in the external barge board.

It works quite well, isn't too noisy, and the external vent is very discrete.

As long as you can use rigid ducting for the bulk of the installation, going over 3m shouldn't be a problem.

Thanks for that - good to know! Yes, I was planning on using rigid ducting. There's a false ceiling in the kitchen and I'm hoping there's enough space to run the ducting there there.

It would need to be rectangular ducting to fit in the space but it looks like you can get circular to rectangular connectors

mldthundercat

We had the exact same. Is upstairs carpeted? We pulled up the floorboards and run it above the ceiling straight outside. Obviously if you have carpet down this may not be an option?

FreeBear

slicendice wrote: »

Thanks for that - good to know! Yes, I was planning on using rigid ducting. There's a false ceiling in the kitchen and I'm hoping there's enough space to run the ducting there there.

It would need to be rectangular ducting to fit in the space but it looks like you can get circular to rectangular connectors

Yup. I have one of these above the extractor hood - http://www.screwfix.com/p/manrose-round-to-rectangular-appliance-connector-elbow-90-bend-white-125mm/22747 - A short length of 125mm flexi connects in to it, and then it is rigid rectangular all the way out to the air brick. Decided against a flappy vent as it would have required a 5" hole through a cavity wall along with a rectangular to round adapter and and an extra bend. The air brick removed the need for a bend & adapter and the hole was much easier to cut.