ProDave Posted July 7, 2016 Share Posted July 7, 2016 Another thread got me thinkng about this and I have to do something very soon. I am a LONG way from deciding which mvhr unit to use let alone from buying it. But I do know where it will be going. It will be in the "plant room" above the garage. I plan to have the intake and outlet vents through the end wall of the room. Now, I will be cladding and rendering this wall very soon. So even though I know nothing else about the system, I really need to fit the inlet and outlet vents through the wall so they can be rendered in. So the question: Are they pretty universal? So can I just buy any make (suggest one and where to buy please) and then it won't matter if I later choose a different make of ducting etc? OR do I have to chose the make of ducting for the entire system now and use that make of wall vent? Second question: The mvhr unit will sit on the floor of the room. So what's a typical inlet and outlet height above the floor of the room? do they go side by side? one above the other? what sort of separation between them? I assume the wall vents connect to the mvhr unit with flexible or semi flexible ducting so there should be a bit of tolereance if my initial "guess" at the vent location is wrong? Link to comment Share on other sites More sharing options...
readiescards Posted July 7, 2016 Share Posted July 7, 2016 I just ordered mine this afternoon. Two 150mm metal tubes and a couple of plastic grills - did not like the look of the metal cowls. And to answer your question (with my limited knowledge) I've yet to choose the final MVHR unit I will use but BPC did not see this as an issue. FYI they need to be a minimum of 1.5m apart Link to comment Share on other sites More sharing options...
ProDave Posted July 7, 2016 Author Share Posted July 7, 2016 got a link to what you ordered and from where? So they can be a long way apart so one each end of the wall for aesthetic reasons will be okay, even though that means one of them will have a longer duct than the other to the mvhr unit.? Link to comment Share on other sites More sharing options...
readiescards Posted July 8, 2016 Share Posted July 8, 2016 BPC 150mm Exterior grill GPVC150 Black and P150-1 150mm pipework x 1 meter (can't actually find it on their website) I'm running these through the wall horizontally and then the connecting tubes will run up from these to actual unit to ensure any rain blown through the grills can not enter into the unit. Link to comment Share on other sites More sharing options...
Gone West Posted July 8, 2016 Share Posted July 8, 2016 (edited) I used rigid 125mm plastic ducting for my MHRV. Where it went through the outside wall I just left about 200mm sticking out and put a cover over it. I did buy a 125mm 90 degree cowl but found out it reduced air flow too much. So I made a wood frame and found a vent cover with a flow area greater than the area of the 125mm duct and fitted that. It's 300mm square. Edited July 8, 2016 by PeterStarck 1 Link to comment Share on other sites More sharing options...
ragg987 Posted July 8, 2016 Share Posted July 8, 2016 We ended up with 180mm steel duct through the timberframe and external render system. I had already specified the MVHR at this point. I suspect the diameter is a function of unit and house size. We used a Airflow DV145 from BPC, the unit itself has 200mm dia outlet / inlets and we needed an adaptor ring. One caution, our MVHR is mounted next to an external wall and the extract run from the unit to the outside is very short - approx 1m long with a 90deg bend. This means that the fan noise goes straight outside, it is quite loud and I fear it will annoy our neighbours in the summer. I will try to add a bit of insulation inside the bend to see if it can be reduced. The inlet run is much longer - about 2.5m and with 2x 90deg bends - and the noise level from that is a lot lower. Link to comment Share on other sites More sharing options...
Bitpipe Posted July 8, 2016 Share Posted July 8, 2016 I also used 180mm steel duct - BPC shipped me two large off cuts ahead of time so I could get them in the wall. Gary at BPC can advise on separation but ours are about 1.5m horizontally and 300mm from finished ground level outside. Link to comment Share on other sites More sharing options...
ProDave Posted July 8, 2016 Author Share Posted July 8, 2016 So it looks like I need to size a unit based on the square metrage of the house to find out what size inlet and outlet ducts it uses, even if it's not necessarilly the exact unit I will be using. Link to comment Share on other sites More sharing options...
PeterW Posted July 8, 2016 Share Posted July 8, 2016 I've got a duct sizing calculator that does the flows etc - admittedly it doesn't calculate the last ones (exhaust/inlet) but most of these are either 160 or 180 mm Link to comment Share on other sites More sharing options...
Jeremy Harris Posted July 8, 2016 Share Posted July 8, 2016 I used 150mm plastic duct (fine for the max airflow with our unit) but did, like Peter Starck above, find that the external fittings restricted the airflow. They also increase the external noise on the inlet, I think. It is surprising how much external noise there is with a short duct on the inlet - the exhaust doesn't seem to make much noise at all, even though the duct is still pretty short. What I've found is that the square plastic external terminals I've fitted, these ones: tend to collect a lot of fluff, spiders webs, dandelion seeds etc on the inlet side and need very regular (as in every two to three weeks in summer) cleaning. I also think they may well be quite restrictive, so I've bought some stainless steel cowl-type external grills that I'm hoping will reduce the flow noise a bit and not get so easily blocked up, like this, but for 150mm duct: Link to comment Share on other sites More sharing options...
Stones Posted July 8, 2016 Share Posted July 8, 2016 150mm pipework is what was specified for our house (by BPC) and we have an internal volume approaching 480m3. I recently took delivery of all my ductwork and MVHR unit. They had included the S/S external cowls pictured by Jeremy above which do look nice and smart, albeit for various reasons we are going out through the roof using 150mm spigot tile vents. Link to comment Share on other sites More sharing options...
ProDave Posted July 8, 2016 Author Share Posted July 8, 2016 I like those SS cowls. Do you want to sell your spare ones Jason? if so I'll buy them then I just need two lengths of rigid ducting to put through the wall. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted July 8, 2016 Share Posted July 8, 2016 I must get around to fitting the new SS cowls I have, I've had them for months and just haven't got around to making up a tapered backing board from a bit of spare larch to allow them to fit flush with the cladding. Be aware that some suppliers charge really silly prices for those cowls, £40 plus each. I bought mine (which are absolutely identical to the one in the photo above, but 150mm rather than 125mm) for a lot less than the price some ventilation suppliers were aslking. IIRC, Mine came from ebay for around £20 each, probably from a seller like this one: http://www.ebay.co.uk/itm/Stainless-Steel-Ventilation-Vent-Outlet-Exhaust-Grilles-100-125-150mm-Ducting-/261528397833?var=560404344005&hash=item3ce44ea809:m:m4MVEHjFVSZC4Zds85pdE1g Link to comment Share on other sites More sharing options...
ProDave Posted July 8, 2016 Author Share Posted July 8, 2016 2 hours ago, JSHarris said: It is surprising how much external noise there is with a short duct on the inlet - the exhaust doesn't seem to make much noise at all, even though the duct is still pretty short. the lesson from that, in my case where for aesthetic reasons I plan to put one each end of the wall, is make the inlet the one that has the long run, and the outlet to the one that has the shorter run. Link to comment Share on other sites More sharing options...
Stones Posted July 8, 2016 Share Posted July 8, 2016 1 hour ago, ProDave said: I like those SS cowls. Do you want to sell your spare ones Jason? if so I'll buy them then I just need two lengths of rigid ducting to put through the wall. No can do - they are boxed up awaiting uplift by courier - BPC realised their mistake before everything had actually arrived and asked me to box them ready for collection. Link to comment Share on other sites More sharing options...
Gone West Posted July 9, 2016 Share Posted July 9, 2016 I bought S/S vent cowls for my system because I thought they looked smart. I then read on a forum, can't remember where, that they reduce the flow of air significantly that is being taken into the MHRV unit. As I am using only 125mm ducting I decided to make my own vent that didn't reduce flow. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted July 9, 2016 Share Posted July 9, 2016 That's a good point, I'll measure up the area of the open intake versus the duct area and see if there is a difference. Certainly the square plastic grilles I have are restrictive, I'm sure. Although they are around 200mm square, a lot of are is taken up by the slats, plus there is a plastic mesh behind the slats that seems to get clogged up fairly easily. One reason for me buying the cowl-type terminals was so that I could angle the intake (which is tucked up right under the eaves overhang) away from the prevailing wind, as one mistake I made was to put the intake and exhaust at right angles to each other, at the corner of the house. Although we've in a sheltered area, the slightest breeze does unbalance the system a lot, as I discovered when I was setting it up. The prevailing wind comes from the right in that photo above, so blows across the intake duct and probably creates a slight pressure reduction at the exhaust terminal. The plan is to angle the intake cowl so that there is also a slight pressure reduction from the prevailing wind, with the hope that this will help reduce the imbalance. I was also hoping that angling it like this might reduce the chance of wind-blown "fluff" getting caught in the grill. Link to comment Share on other sites More sharing options...
Guest Alphonsox Posted July 9, 2016 Share Posted July 9, 2016 I have actually doubled up the roof vents for our system - so two inlet and two outlet run in parallel. I wasn't convinced that single vents wouldn't restrict the flow. The roof vent are pretty much invisible and the cost of a couple extra and some extra piping was minimal. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted July 9, 2016 Share Posted July 9, 2016 6 minutes ago, Alphonsox said: I have actually doubled up the roof vents for our system - so two inlet and two outlet run in parallel. I wasn't convinced that single vents wouldn't restrict the flow. The roof vent are pretty much invisible and the cost of a couple extra and some extra piping was minimal. Not a bad idea, provided it doesn't increase heat loss from bridging. As this has come up again I'll try and fit the less restrictive terminals in the next week or two and see if that reduces the intake noise. If it does, then that's a reasonable indication that it may well have also reduced any flow restriction, as often flow restriction causes additional noise. Link to comment Share on other sites More sharing options...
Stones Posted July 9, 2016 Share Posted July 9, 2016 7 hours ago, Alphonsox said: I have actually doubled up the roof vents for our system - so two inlet and two outlet run in parallel. I wasn't convinced that single vents wouldn't restrict the flow. The roof vent are pretty much invisible and the cost of a couple extra and some extra piping was minimal. Was it concerns about noise or purely down to airflow that made you double up? Out of interest, what is your internal house volume? Link to comment Share on other sites More sharing options...
le-cerveau Posted July 10, 2016 Share Posted July 10, 2016 Joining in with a similar question. My house will have a significant MVHR requirement, 419-423m2 Floor area (depending on the day I measure the plans) and a volume of approx 1300m3! That gives me a vent flow rate of 458 m3/h (UK Building Regs), even using 0.3 ACH it is nearly 400 m3/h so quite high. I am looking at a unit in the 700-900m3/h range so that it runs at around 50% normally and these come with 200-250mm terminals. All the terminals I have seen appear to max out at 180mm, without going commercial, although the MVHR unit will most likely be form the light commercial range. Do I look at the commercial range of terminals or split to 2 x domestic? I haven’t decided on roof or wall terminals yet and either is a possibility, NNW elevation would go through a gable wall ENE through the roof, prevailing wind SW. Link to comment Share on other sites More sharing options...
Alexphd1 Posted July 10, 2016 Share Posted July 10, 2016 Le-cerveau. Problem with commercial units they take a large price jump. Vent axia has just launched a larger model kinetic high flow which would probably do you just fine. Before this unit was on market I was looking at two domestic models. Link to comment Share on other sites More sharing options...
Guest Alphonsox Posted July 10, 2016 Share Posted July 10, 2016 8 hours ago, Stones said: Was it concerns about noise or purely down to airflow that made you double up? Out of interest, what is your internal house volume? I put them in for primarily to improve airflow, the house is around 650m3 in volume and hence is at the upper end of what can be achieved with a single "standard" MVHR. Additionally this gives me the option of separating the MVHR for the main house from the annex at the rear if it ever becomes necessary. Link to comment Share on other sites More sharing options...
PeterW Posted July 10, 2016 Share Posted July 10, 2016 1 hour ago, Alexphd1 said: Le-cerveau. Problem with commercial units they take a large price jump. Vent axia has just launched a larger model kinetic high flow which would probably do you just fine. Before this unit was on market I was looking at two domestic models. The converse is the commercial ones appear on eBay quite cheaply but they're not SAP-Q listed so you end up going with lower efficiencies in the calcs. I will post the quick and dirty calculator later that may help you with flows etc Link to comment Share on other sites More sharing options...
readiescards Posted July 10, 2016 Share Posted July 10, 2016 On 08/07/2016 at 16:02, JSHarris said: What I've found is that the square plastic external terminals I've fitted, these ones: tend to collect a lot of fluff, spiders webs, dandelion seeds etc on the inlet side and need very regular (as in every two to three weeks in summer) cleaning. Gosh I don't want to be going up a 3 storey ladder every few weeks to clear some fluff - might need to have a think how to clean the vents from inside 1 Link to comment Share on other sites More sharing options...
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