Yes it's permitable but its a cop out, grease and water will collect in the "corrugations". Much better that the duct is in rigid plastic, either round or rectangular in section. Its a good idea to check the hood instructions to check the size of the duct that is required.
Many thanks for your reply. I will check outlet of hood. I was meaning to ask about flexible pvc through a unsleeved wall too - is that allowed? Is easipipe range the cheapest as I need 2 x 2 metres of round pipe as there is plenty of space on top of units.
I would say that flexible ducting through the wall is a bad practice, if you have to use flexible ducting it should terminate before the wall and be change to rigid. Use any combination of this lot (except the flexy of course ) http://www.screwfix.com/cats/100139/Heating-Cooling/Ducting
Thanks for information. I`m just trying to put right what has already been done in my 3 month old terrace house. Screfix may not do 100mm round rigid pipe in any longer lengths than 350mm. Website says 350 x 1000mm though picture looks like 1m x 100mm
Don't worry, it is 1m long. Don't forget these (in the right size) http://www.screwfix.com/prods/46702/Heating-Cooling/Ducting/Pipe-Connector-120mm
Thanks for that. Just one more question please - how do I join 100mm flexible aluminium to 100mm rigid platic duct pipe as I wish to replace the existing pvc bent/drooping/sagging stuff already fitted?
voids, its rigid & work ok. That's OK if the extractor is designed to work on 4", but some of the larger extractors need 5", even 6" for some of the fancy machines designed to work over large ranges.
bent/drooping/sagging stuff already fitted? Is it not possible to replace all the flexy stuff or is this the bit thats plastered into the wall? The same jointing piece as I mentioned above should do the job, it's possible that the flex may fit over the 100mm pipe, either way it needs to be secured with a large jubilee clip or duct tape. For that matter all the joits should be taped.
Thanks - very grateful for your help The pvc stuff is through wall and not plastered hence draught inside kitchen. Not even secured to outlet plate. The ali flexible I intend to fit is for another fan that is 2.9 metres away from another outlet in flexi pvc. I only intend using ali where it is behind false wall - say 500mm then the rest of the way will be in 100 rigid. Originally the builders fitted 3 x 20watt fans axial type on pvc runs of at least 2.9 metres, 3.5 metres and 4.5 metres. I quoted building regs and they changed them to better silavent centifrugal fans with back draught shutters. I may have problems with any future replacement of the ist floor bathroom and ensuite ducting that is done in flexible pvc as it is in the ceiling and under the 2.5 storey bedroom floor. Two of the original fans had no back draught shutters and we are only 110 metres from the north devon sea wall! (less in high tides?).
Ah I see your problem, given that it's all new building work then they should have designed in rigid PVC. If you have long runs then as has been said you can use 4" drain. Just had a thought (slow in the mornings) these long runs weren't flexy , were they? Just one other point, make sure that the outside vents have a sheltered shutter, something like this http://www.screwfix.com/prods/14789/Heating-Cooling/Ducting/Cowl-Vent-Brown
Thanks again All the extractor fans are currently in flexible pvc 100mm. I do not think this fails regs with a centrifugal fan fitted. Looking at the web sites I learnt that one can only use axial up to 1 or 1.5 metres in flexible. The en-suite and The bathroom 3.5 and 4.5 metres ducting in flexible pvc have only the silavent integral shutters on as the external vents are in the upside down soffit? postion The kitchen and cloak room are 1.5 metres and 2.9 metres and have back draft shutters on the external vent in the vertical position. Just going to look at the outlet size from the cooker hood and see if 100mm is enough. exsolar heating engineer of 26 years here not a salesman
Hi, running a 150mm rigid duct under the floor for a downdraft extractor fan from the kitchen island. the duct will be slanted slightly upwards to help air leave room, and approx. 2.5m long. my first question - can I use a 150mm plastic (round) pipe (such as a drains pipe) ? or are there building regs ? I'm not exactly sure how hot the pipe will get. secondly- I'm fitting the duct slanted, as per guidance in the instructions. but surely this will lead to condensation coming back into the pipe? (and being below the ground hold water)
It's only hot air,& it cools pretty quickly, pipe is rated to around 75 defree centigrade for hot water, so ok. Vent pipe needs to slope downwards to the outside vent, so any moisture can run out, want to insulate pipe to stop warm air condensing back to water.
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