GaryChaplin Posted January 10, 2023 Share Posted January 10, 2023 Hi all, Firstly, hello! This is my first post, so apologies if this has been asked before. I'm part way through a true self-build and I have designed in a MVHR system. I have received a quote for a company install, but I'm simply not prepared to pay the ridiculous costs for essentially running pipes into every room. There seems to be much talk about commisioning and flow rates etc? Can anyone point me in the direction of some guidance so I start my research in the correct place? I have to use 90mm pipes and intend to have 3 extracts and 4 supplies. It's an intentionally small passivehaus inspired build, so hopefully should not be too complex. Thanks, Gary. Link to comment Share on other sites More sharing options...
MJNewton Posted January 10, 2023 Share Posted January 10, 2023 (edited) 21 minutes ago, GaryChaplin01 said: Can anyone point me in the direction of some guidance so I start my research in the correct place? I think you've found it! Seriously, I can't imagine a better place to start than a (sub-)forum dedicated to the subject. You'll learn far more through ploughing through old threads on here than any book would likely tell you. Sure, it'll be very unstructured and out-of-order but you'll be covering nuances and aspects of design that would be overlooked in any attempt at a concise summary. Just have a meander through letting things flow over your head as familiarity grows and before long you'll be an 'expert' (okay, a self-proclaimed one but the label is only being sought to give yourself confidence that this is DIYable, which it most definitely is - and to a potentially better outcome than getting the pros in). Edited January 10, 2023 by MJNewton 1 Link to comment Share on other sites More sharing options...
GaryChaplin Posted January 10, 2023 Author Share Posted January 10, 2023 Thanks, I sort of guessed that as immediatly regretted posting the question before reading some of the previous messages! Much to learn, looks like a great resource... 1 Link to comment Share on other sites More sharing options...
Conor Posted January 10, 2023 Share Posted January 10, 2023 Sounds like an easy case for DIY. You'll have a single, small unit, two manifolds and no more than 12 ducts in total. No reaon why you can't get the job done for less than £2k. Assuming no strange beams stopping direct routes and a central ish location for the unit Link to comment Share on other sites More sharing options...
Adsibob Posted January 10, 2023 Share Posted January 10, 2023 Many companies will give you a basic design for a nominal sum. May be worth doing, unless you are happy to post 3D drawings of your wall and ceiling layout here for others to comment on (with details of joists, steels and other potential obstructions). You obviously don’t have to do that, but if it was me I would want the peace of mind that somebody had gone over the design and given it a thumbs up. My top recommendation is to use posi joists (if you are using joists at all) and to consider the Lindab Airy vents for the bedrooms as they are super quiet. You should also over spec your unit, so that it is running well below max. Link to comment Share on other sites More sharing options...
JohnMo Posted January 10, 2023 Share Posted January 10, 2023 16 minutes ago, Adsibob said: My top recommendation is to use posi joists +1 on that. The best change that happened on our build, original build had lots of wood and little of places to get pipes in and out of places. Posi joist/rafters are great. Also speed up the build as they are easy to move about due to the lower weights. Link to comment Share on other sites More sharing options...
GaryChaplin Posted January 10, 2023 Author Share Posted January 10, 2023 (edited) Thanks for the replies. The primary construction is oak frame and in hindsight I would have considered the MVHR before the initital design. However it was designed and built as a well insulated barn, then permission gained for conversion to residential. I have the design modelled in sketchup, but it may not be clear from the following drawing as it's pretty cluttered. I plan to run the pipes vertically stacked along one wall in a hidden cavity within the insulation envelope. Red indicates extraction, blue is clean air. It's only a 1 1/2 storey build with a very open and simple layout. Extracts from kitchen, bathroom & utility. Elevations.Plans.Sections.ServicesPlanning_V7.pdf Edited January 10, 2023 by GaryChaplin01 Link to comment Share on other sites More sharing options...
Adsibob Posted January 10, 2023 Share Posted January 10, 2023 You are meant to supply air fairly close to windows, otherwise risk of condensation, within 40cm to 50cm of a windows should be fine. And in bathrooms you want to extract close to the centre of the room, but taking into account window position as well. Does your design allow for that? 1 Link to comment Share on other sites More sharing options...
MJNewton Posted January 10, 2023 Share Posted January 10, 2023 2 minutes ago, Adsibob said: You are meant to supply air fairly close to windows, otherwise risk of condensation, within 40cm to 50cm of a windows should be fine. Can you elaborate on that? It's not something I've seen/heard before. My understanding is that the primary driver for the location of supply vents is such that maximum cross-flow/mixing of air is achieved through the room thus, usually, being as far from the door (through which the air is ultimately expelled) as possible. The exception to this is large mixed-purpose rooms (such as 'family' rooms that might combine lounge, kitchen and dining areas) which contain both supply and extract vents, but again the same principle of maximising distance between supply and extract holds true. 2 Link to comment Share on other sites More sharing options...
GaryChaplin Posted January 10, 2023 Author Share Posted January 10, 2023 I've tried to design the system with the most amount of through flow. I can't see why the vents being by the windows would have any bearing on condensation. They will be triple glazed and I hope the MVHR will deal with moisture content. Link to comment Share on other sites More sharing options...
Nickfromwales Posted January 10, 2023 Share Posted January 10, 2023 21 minutes ago, Adsibob said: You are meant to supply air fairly close to windows, otherwise risk of condensation, within 40cm to 50cm of a windows should be fine. And in bathrooms you want to extract close to the centre of the room, but taking into account window position as well. Does your design allow for that? I would disagree with the above ( sorry again ). I almost always install these in corners of the rooms, diagonally opposite the doorway wherever practicable. 2 Link to comment Share on other sites More sharing options...
Nickfromwales Posted January 10, 2023 Share Posted January 10, 2023 1 minute ago, GaryChaplin01 said: I've tried to design the system with the most amount of through flow. I can't see why the vents being by the windows would have any bearing on condensation. They will be triple glazed and I hope the MVHR will deal with moisture content. Yup. Link to comment Share on other sites More sharing options...
RandAbuild Posted January 10, 2023 Share Posted January 10, 2023 I think you are right about maximising cross-flow and mixing. It's important to leave a 10-15mm gap under doors to allow this. I attach plans of our self-install. You'll see some of the pipework is doubled up on longer runs or those where you want higher flow. It's good you are inside the insulation envelope but how good is your airtightness? the better it is, the better the MVHR will work. Link to comment Share on other sites More sharing options...
joe90 Posted January 10, 2023 Share Posted January 10, 2023 I designed my own, used “I beams” and holes cut in these for ducts is easy, I bought a 6 inch hole cutter! like @Nickfromwales says above my vents are opposite corners to doors for through ventilation, never got round to measuring flow rates (but it works ok). I even DIY made my manifold/silencer and room vents. 👍 Link to comment Share on other sites More sharing options...
GaryChaplin Posted January 10, 2023 Author Share Posted January 10, 2023 I can't beleive how responsive this forum is! Many thanks to all for such prompt discussion! 😀 Air tightness should be excellent. The entire build has a seamless and taped insulation envelope, with two breather membranes and further insulation taped on the inside! Link to comment Share on other sites More sharing options...
joe90 Posted January 10, 2023 Share Posted January 10, 2023 19 minutes ago, GaryChaplin01 said: I can't beleive how responsive this forum is! Well you will get advise from a diverse bunch from the professionals down to the “I am sure I can make that in my shed” (I fall into that category). I have learnt so much from this forum during my build and now (hopefully) I can share the knowledge I have gained. We won’t all agree on everything but you can get a general idea what’s best for you. 👍 Link to comment Share on other sites More sharing options...
Adsibob Posted January 10, 2023 Share Posted January 10, 2023 (edited) The window point is not set in stone, but the point I make is as follows: Trickle vents are required on all windows by building regs. There are a couple of exceptions, one of which is if you have MVHR you don't need trickle vents. Condensation on windows can occur if there is insufficient ventilation. If you install the vent as far away as possible from the door (say in a diagonal) there will be some room designs/layouts where the window might be quite far from the main corridor of airflow. It's unlikely, but possible. So i'm just saying to take that into account. 1 hour ago, RandAbuild said: It's important to leave a 10-15mm gap under doors to allow this. And as for the gap under the door, this is a function of the width of the door: height of gap = 7600/width of door So you will only need 10mm or more if you door is 760mm wide or less. If you can go for big doors (anything above 825mm) then you can reduce the gap 9mm or less. The lower the gap the more elegant the door, so we have fitted the largest doors we could accommodate. Most are 838mm, but one is 926 and we have a double door where the gap is only 6mm. Edited January 10, 2023 by Adsibob Link to comment Share on other sites More sharing options...
MikeSharp01 Posted January 10, 2023 Share Posted January 10, 2023 6 hours ago, MJNewton said: You'll learn far more through ploughing through old threads on here than any book would likely tell you. Sure, it'll be very unstructured and out-of-order but you'll be covering nuances and aspects of design that would be overlooked in any attempt at a concise summary. There is a relatively well known, although I cannot find it right now, piece of research which says that there is a sweet spot in the problem solving, information gathering space which says that there comes a time, after the sweet spot, where you are managing so much information that it starts to damage you ability to solve the problem. So watch out for that, but otherwise enjoy! Link to comment Share on other sites More sharing options...
MikeSharp01 Posted January 10, 2023 Share Posted January 10, 2023 1 hour ago, Adsibob said: It's important to leave a 10-15mm gap under doors to allow this. Yes but not on external doors. 1 Link to comment Share on other sites More sharing options...
MJNewton Posted January 10, 2023 Share Posted January 10, 2023 39 minutes ago, MikeSharp01 said: There is a relatively well known, although I cannot find it right now, piece of research which says that there is a sweet spot in the problem solving, information gathering space which says that there comes a time, after the sweet spot, where you are managing so much information that it starts to damage you ability to solve the problem. So watch out for that, but otherwise enjoy! ‘Analysis paralysis’? If so, yes, I’m a regular at that!! Link to comment Share on other sites More sharing options...
Adsibob Posted January 10, 2023 Share Posted January 10, 2023 5 minutes ago, MJNewton said: ‘Analysis paralysis’? If so, yes, I’m a regular at that!! Me too Link to comment Share on other sites More sharing options...
Nickfromwales Posted January 10, 2023 Share Posted January 10, 2023 2 hours ago, GaryChaplin01 said: I can't believe how responsive this forum is! Oops.... I take it you've not properly read the forum T&C's? If you brag it up too much and you've less than 10 posts, you have to buy everyone a pint. Sorry matey, rules is rules. Check the small-print next time eh 1 Link to comment Share on other sites More sharing options...
RandAbuild Posted January 10, 2023 Share Posted January 10, 2023 4 hours ago, Adsibob said: Condensation on windows can occur if there is insufficient ventilation. After nearly 5 years, we've never had any condensation on the inside of our triple glazed windows, anywhere. I think this is entirely down to the MVHR 1 Link to comment Share on other sites More sharing options...
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