stuart60285

Also - what is the difference between these two plenums? What do you get with the £40 one vs the £23 one? £23: https://bpcventilation.com/collections/semi-rigid-radial-ductwork/products/quiet-vent-90mm-plenum?_pos=5&_fid=72520b439&_ss=c £40: https://bpcventilation.com/collections/semi-rigid-radial-ductwork/products/90-90mm-plenum?_pos=8&_fid=72520b439&_ss=c

Hi everyone - long-time lurker. We are in a Redrow house, and I am at the point where I want to retrofit MVHR. I have planned where we can run ducting which shouldn't be a problem and have estimated our airtightness to be around 0.3-1ACH via CO2 monitors. Main thing left to do as preparation is to move wardrobes out of the way in 2x bedrooms and do some exploratory holes to confirm we clear joists for the downstairs pipework drops. Until I do that however, I would value some input into the design I have done please. Goals The primary goal is improving comfort in the house. We find the house is either under-ventilated and stuffy, or overventilated and cool/draughty. With the MVHR, we would like fresh air throughout the day without the need for trickle vents or windows open, letting in cold air. We would also like noise to be kept to a minimum and be able to remove smells from cooking in the kitchen area quickly. Secondary goals are improving the air tightness in at least some of the rooms (mainly bathrooms/utility due to there being 100mm holes to the outside via extractor fans) and possibly reducing heating bills. The secondary goals are not essential. Ventilation Rates I have used the Paul Heat Recovery spreadsheet to work out my ventilation rates. Given the air volume we need, the goal around noise and kitchen smells, and the good amount of space we have available for pipe runs in the loft (as I perceive it - maybe these pipes take up a lot more room than I realise?), I am leaning towards 90mm round ducting to get the volume we need at the lowest flow rate. I have included a screenshot of the spreadsheet below: MVHR Placement + Primary Duct Work The MVHR unit will be in a cold loft. I recognise this is not ideal, but the space is well lit, easily accessible, and I can place insulation over the unit. As for the primary ductwork to the outside world, I am a bit unsure of the best way to approach this - we do have roof tile vents already for extractor fans, all of which have 125mm or 150mm connections (can't remember which - need to confirm). I understand that you can get MVHR roof tile vents, but is the difference significant enough to be of concern given our ventilation requirements? If not, options will be to get MVHR tile vents fitted, or maybe sofit vents? Condensate drain - I am hoping I can just run this into guttering/gutter downpipe. Will insulate the pipe from the MVHR unit to the outside. Has anyone done this? As for the distribution manifolds, these will be located in a similar area to the MVHR unit and I am aiming for that to be below the loft insulation. Upstairs Ducting Runs These will all originate in the loft and be run under insulation. I am not particularly concerned with space for this as the routes the pipework will follow are largely clear of other services. I am hoping to run them all in the V shape between the truss webs as that will make installation quick(er) and easy(er). The picture below highlights these runs. The 3x supply and 3x extract to the upstairs rooms should be fairly simple. I have put the master bedroom supply in the walk-in wardrobe area (which has no door - we removed that as it was pointless), as this likely means no sound for us. I presume there would be no issue with that? Downstairs Ducting Runs For downstairs, I plan to run 3x supply and 3x extract down behind some fitted wardrobes we have (they are easily to remove for the installation). I believe I need to consider risk of fire spreading with these as there will be holes in the ceiling upstairs and through the floorboards - does anyone know of any specific things I need to do to mitigate this other than intumescent seals around the pipes? For the supply, these should drop down into the ceiling downstairs and run parallel to the joists. I intend to run 2x 90mm ducts to the family room area to provide high flow of air for when we want to remove cooking smells. For the extract, these will drop down below the ceiling into the utility room, as the I-joists run perpendicular to the ducting runs so I can't drill 90mm holes in them. I am not that bothered about this however, as they come into the utility room and wont be noticeable once boxed in. The kitchen will get 2x 90mm pipes into a wall plenum - once again to provide a high extract rate when cooking. The other duct will run to the downstairs toilet. I think I will need extract in the utility room too? My thoughts are to either tee-off the 90mm duct to the downstairs toilet, and have an extract for the utility coming off the same pipe. Will cross-talk be much of an issue with that? I could consider doing the teeing-off in the loft and just run 2x 75mm ducts instead of that one 90mm duct? Thoughts? Does anyone have any wisdom to offer on the above? There is an element of fuzziness in the design r.e. where things are placed as inevitably something will get in the way. I plan to get the ducting and distribution boxes in first as that will take a while to do (will be doing this on weekends), and using a to-scale mock-up of the MVHR unit in the interim until I am ready for the unit to be fitted and commissioned. Thank you for reading and any comments you leave.