One vent for 2 extractors, under floorboards?

[HappyHippyDad]

I have to get a kitchen extractor and shower room extractor vented outside.

They are back to back to each other on the ground floor.

There are no external walls that lead to the outside.

I can run the ducting under the floorboards between the same joist (both extractors) all the way to the outside (approx 5m). Both extractors have one way valve on them.

My questions are;

1. Could I tee the ducting together with a Y shaped piece towards the end of the duct near the outside vent so it's just one vent on the outside wall?

2. Would I need additional one way valves put in the ducting? I cant see why, but years ago a building inspector insisted on it. My worry is that if the additional valves get obstructed/become faulty there will be no access to them under the floorboards.

3. The kitchen extractor will be more powerful than the shower. I have seen this once before and I noticed a marked drop in the efficiency of the shower fan if the kitchen fan was on. However, I have lived at my house for 10 years and never had both fans on at the same time whilst having shower. Even if it was once a year I can't really see this being a problem?

Thanks all.

 

[Wilko]

Hi - I'm just a simple person, so I'd try to get one outlet per fan, so no back draft or capacity issues. But if that's not possible your one way valves sound sound .

 

[Midwest]

Two into one don't go, without suitable protection.

 

[Toneyz]

Why can't you duct both of them separately?

 

[Marvo]

Does the shower room have a toilet in it?

Firstly I don't know what the UK building regs say about this but if you're mixing two systems in the same ducting I'd only do it if the whole system is under negative pressure to prevent backflow and crossover. This means the fan would be at the point of discharge and both systems would run simultaneously.

Using a positive pressure common duct gives inconsistant performance depending on which fans happen to be running, there's a high liklihood of backflow/crossover. There may be fire regs issues if there's a kitchen involved and there may be hygiene issues if one of them's a toilet.

My gut feel from the description of your system is that you should keep both systems completely separate if at all possible.

 

[Bellendian]

I've asked this question of building control before, kind of knowing the answer but chancing my arm!
Not surprisingly they said no. 2 ducts required.

 

[123]

It sounds like a terrible idea to combine the two. Kitchen Cooker Hoods generally need at least a 5 inch duct as well, some need 6 inch.

Cooking a big fry up with possible back feeds might be a way to get the wife and daughter out of the shower quicker though.

 

[Nigel]

Def a no go. As Marvo has said you will have issues with oressure that will play havoc with the fan motors. Clearly hygene issues also.

 

[HappyHippyDad]

Thanks for all the replies chaps. I was back at the job today and core drilled another hole and got 2 separate lengths of ducting in. I feel far happier with that than with my initial suggestion.

 

[Midwest]

Its good to talk.

 

[Gary K]

Cooking a big fry up with possible back feeds might be a way to get the wife and daughter out of the shower quicker though.

And wife/daughter on the loo with possible feedback may get everyone out of the kitchen quicker!

 

[Marvo]

Thanks for all the replies chaps. I was back at the job today and core drilled another hole and got 2 separate lengths of ducting in. I feel far happier with that than with my initial suggestion.

I think you did the right thing and avoided a lot of future headaches.