pritch Posted June 20, 2019 Share Posted June 20, 2019 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 Link to comment Share on other sites More sharing options...
lizzie Posted June 21, 2019 Share Posted June 21, 2019 Are you having MVHR? If so then an extract to outside is generally not advised. Link to comment Share on other sites More sharing options...
ryder72 Posted June 21, 2019 Share Posted June 21, 2019 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. Link to comment Share on other sites More sharing options...
Big Jimbo Posted June 21, 2019 Share Posted June 21, 2019 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 % Link to comment Share on other sites More sharing options...
ryder72 Posted June 22, 2019 Share Posted June 22, 2019 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. Link to comment Share on other sites More sharing options...
wozza Posted June 23, 2019 Share Posted June 23, 2019 Look at Compare ducting - their rectangular duct corners have vanes to help direct the air to reduce turbulence. Link to comment Share on other sites More sharing options...
Swampy Posted June 18 Share Posted June 18 On 20/06/2019 at 22:58, pritch said: 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 Hi, What did you do in the end? I'm interested, because I face the same choice and under the same tight deadlines. Link to comment Share on other sites More sharing options...
JohnMo Posted June 19 Share Posted June 19 On 20/06/2019 at 22:58, pritch said: 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 12 hours ago, Swampy said: What did you do in the end? I'm interested, because I face the same choice and under the same tight deadlines. Why bother extracting, can you not just recirculate, via a grease and carbon filter? Then the air comes out at you kick board. 2 Link to comment Share on other sites More sharing options...
Swampy Posted October 16 Share Posted October 16 (edited) On 19/06/2024 at 12:40, JohnMo said: Why bother extracting, can you not just recirculate, via a grease and carbon filter? Then the air comes out at you kick board. As I understand it, recirculating doesn't remove moisture from the air, so you're getting rid of pollutants, but not moisture. Extracting the air from your cooking is better. We went the extraction route through the floor (needed to set up the ducting before underfloor heating and screeding was installed), and it's working really well. Very happy with the outcome. We didn't have the option to route ducting extract through the ceiling space and didn't want it to be visible. Edited October 16 by Swampy Link to comment Share on other sites More sharing options...
JohnMo Posted October 16 Share Posted October 16 16 minutes ago, Swampy said: you're getting rid of pollutants, but not moisture. Extracting the air from your cooking is better Why is it better? Your MVHR handles moisture already, so do you really need a second method? As I have said before we rarely ever use the cooker hood now the house has dried out, just don't need to. Link to comment Share on other sites More sharing options...
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