Extractor fan ducting

[MarkK]

Is it OK to run 3m of extractor ducting (for a cooker hood) between the kitchen ceiling, which is plasterboard, and a bedroom floor, which is T&G floor boards?

I'll be using 125mm ducting. I'm primarily concerned about building regs & fire risk, but would guess the temperatures involved shouldn't normally be a problem. The joists run in the right direction and there are no obstructions, so in principle it looks straightforward.

I'm planning on buying the ducting from Screwfix.

Any advice, or alternative suppliers would be appreciated.

Mark

[JoeJoe]

[David Hansen]

On Wed, 12 Jul 2006 00:09:33 +0100 someone who may be "MarkK" wrote this:-

Will this pass through any walls, other than the external one.

From what materials will the ducting be constructed?

Is the ceiling and/or floor designed to be fire resistant? If so, for how long?

[Ian_m]

My brother, a building consultant, put my kitchen ducting in a fireproof box. He has seen numerous cases where the extractor hood fan motor has caught fire (possibly due to dirt and grease) and the fire then passed through into the ceiling space before entering the room above.

The boxing was made with plasterboard (spare bits of 15mm sound block plasterboard in my case) with gaps sealed with fireproof mastic. There were a couple of peices of wood (to hold the plasterboard in place) in the cavity, which were covered with expanding fireproof foam.

I got the mastic and foam from Travis Perkins, but I notice Screwfix sell also.

Also fitted an intumescent collar to a waste downpipe passing through the kitchen (behind boxing) as he has seen a kitchen fire pass into the down pipe and get into the room above. The collar crimps the pipe off from the heat of a fire, again Travis Perkins.

[MarkK]

No

Not finalised, but how about:

?cId=100139&ts=44140&id=17489 >I'll be using 125mm ducting. I'm primarily concerned about building regs &

I don't think either ceiling or floor above are designed to be fire resistant. House is 1950-built 2-storey.

[MarkK]

Thanks - good info. I'm going to have to re-think this.

Mark

[David Hansen]

On Wed, 12 Jul 2006 23:45:41 +0100 someone who may be "MarkK" wrote this:-

Assuming the flexible ducting is metal then I see no problem. Make sure it slopes down gently to the terminal. I certainly wouldn't bother with intumescent collars.

[Lobster]

If one guy has genuinely seen numerous cases that implies this is a really common problem. How many is 'numerous'? I've never heard of this issue.

David

[MarkK]

I could've said "plastic & metal" but for all I knew you may have wanted to know the type of plastic, etc. Linking to the items I'm considering allows people to respond with "they're fine" or "don't use that" type responses.

By terminal I assume you mean the outlet to atmosphere, and that the sloping down is to allow any condensate to drain away from the extractor unit?

Mark

[David Hansen]

On Thu, 13 Jul 2006 18:07:44 +0100 someone who may be "MarkK" wrote this:-

Correct on both counts.

Long vertical runs of ducting should have traps and drains, largely because water and normal electric motors don't mix, but also because water dripping out of the hood is not appealing. However, there should be no problem with a short vertical run to the ceiling and then a constant downward slope from there.