Downdraft extractor under floor

[pritch]

Hi

I'm thinking about having a downdraft extractor in my kitchen island rather than a hood. I don't really want to be cutting holes out in my new flat roof so I'm thinking of extracting out under my floor using the flat extract system. 

The 100mm insulation and 80mm screed is about to go down next week so I need to decide asap. 

My only concern is on top of the 100mm insulation will be my underfloor heating pipes. 

The 60mm flat extract would go into the cut out insulation I guess ? 

I'm also worried about  heat loss due to the extract pipe going straight out the side of the house from under the floor. 

Has anyone done their extract in a similar way?

Thanks 

 

 

[lizzie]

Are you having MVHR? If so then an extract to outside is generally not advised.

[ryder72]

What type of extractor are you having. a 60mm flat extract sounds like an ultra low profile system and will cause tremendous pressure loss. If you are looking at a vented hob or  a decent downdraft, you really ought to be thinking of using a 89 * 220mm system, ideally with rounded profiles and deflectors for optimum performance.

 

This would be set into your PIR insulation layer and screeded over. The heat loss on account of the heating pipes in the screed will be miniscule compared to what you would lose from any other venting system.

 

If you have MVHR then recirculate and ensure that you have an extract vent provided in the ceiling in the vicinity of the hob.

[Big Jimbo]

Any of the super posh, and expensive manufacturers will state the size of the pipe required. The cheaper one's won't bother. It's quite often 250mm round. The 60mm stuff you are looking at will be rubbish. Even the 90 x 220mm stuff could well be to small. Although above my intel level, one of the expensive manufacturers was trying to explain to me that a swept 90 degree bend, in the extract pipe work would reduce the efficiency by 30 %

[ryder72]

16 hours ago, Big Jimbo said:

Any of the super posh, and expensive manufacturers will state the size of the pipe required. The cheaper one's won't bother. It's quite often 250mm round. The 60mm stuff you are looking at will be rubbish. Even the 90 x 220mm stuff could well be to small. Although above my intel level, one of the expensive manufacturers was trying to explain to me that a swept 90 degree bend, in the extract pipe work would reduce the efficiency by 30 %

 

 

Sorry but what you are saying is simply NOT TRUE.

 

150mm round or rectangular equivalent (90*220) is the industry norm and the 'super posh and expensive manufacturers) specify exactly this size. The rectangular duct has a larger cross section to offset the greater drag caused by a larger contact area.

 

250mm round is actually a 10 inch duct which is what is used on commercial HVAC systems or restaurant kitchens. I would like to see where and how you could build this into a domestic dwelling ? though I do agree that the performance will be great.

 

90*220mm ductwork is absolutely fine.

[wozza]

Look at Compare ducting - their rectangular duct corners have vanes to help direct the air to reduce turbulence.