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Hi guys, 

Wondering if anyone with experience of MVHR in new builds can advise me on a few things.

Essentially I'm working on my self-build and I'm just wanting to make sure I'm correct about some of the building regulations regarding the installation of MVHR.

So the house will have the following dimensions:

Basement area - 210m2 (504m3)

Ground floor - 210m2 (504m3)

First floor - 135m2 (324m3)

Second floor - 135m2 (250m3)

Total 690m2 (1588m3)


Some additional info is that there are potentially 7 bedrooms, 1 kitchen, 1 utility and 7 bathrooms. The number of occupants on a daily basis will be 4, however we will likely have up to 10 people total staying in the house at any one time. 


Now my questions were regarding the size of the MVHR I need to spec. I understand that according to building regs, the rate of exchange should be a minimum of 0.3l/s/m2, which based on my 690m2 of space gives me a system that can handle 207l/s (745m3/hr). Firstly, can anyone confirm that I have understood this properly? And then my second question is that whilst we do have a large space, the number of inhabitants most of the time won't be particularly high and some of the spaces, eg loft and basement space, won't be used on a daily basis - so would I be able to get away with using a system that just passes building regs (eg. one that can cope with say 800m3/hr - Daikin Air Conditioning Ducted Heat Exchanger VAM800J; or Lg Air Conditioning Eco V Heat Recovery Ventilator LZ-H080GBA5; or potentially a couple of the ), or would I need a system with a much higher potential capacity (eg ~1000-1500m3/hr - eg the LG heat recovery ventilator LZ-H150GBA5)? Was hoping those of you that own MHVR's and have experience using them can help me advise me as to whether Building regs requirements are over the top and in reality the system wouldn't need to work anywhere near as hard to meet our needs. 


Also if anyone has any suggestions with any particular brand or heat exchanger then please feel free to recommend. I've explored the options from Titon and Zehnder but it seems I would need two of their systems to cope with the floor space - putting us at ~£4.5k for the systems; whilst the ones I've suggested above are approximately half of that so whilst they have a slightly lower efficiency (80%) I figured the extra for the Zehnders wouldn't be worth the time it would take to recover the extra £2-2.5k. Opinions welcome though! :) Thank you in advance

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for a build that size I would be getting a professional to design the MVHR system. I'm sure it'll be a very small % of the overall budget and it's not something I would want to get wrong.


I used Enhabit for our 450m2 self-build with a basement and was very happy with their fees and design.

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Fully agree with Thorfun, that is a big project & should be designed professionally from the start. It may even require more than one unit?


I used BPC ventilation for my current house design which was a retrofit & found them really good as have many others on here. I think it cost around £100 for them to do the design/layout/rates etc.

I am using Blauberg for my self build, again around £100 for the service & very helpful.

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My house is about 50-60% footprint of yours (remember for MVHR calcs you only measure useable interior space so not inc. walls) but similar in design of basement (4 rooms + plant), 6 beds (inc rooms in roof) and 4 bath/wc. 


BPC designed me a system based on Sentinel Kinetic + which easily met the BR whole house ventilation requirement at just over 40% fan speed and since, like you, there are only 4 of us I dialled it down to a more comfortable 35% for normal, keeping boost at 50%. You need to show to BR (in that you mark your own homework, they will never check) that your system can meet the regs but how you configure it there after is up to you).


That unit is designed for multi occupancy units and was about £2k ish in 2015, I think it's about 30% cheaper now.


The design was useful to size the unit and also estimate the ducting, although they made a generous allowance for deviation in runs which was needed (I diy installed and commissioned - lots of threads on this site how to do that). I used 75mm flexi duct with double runs to all extracts (7) and single to all supplies (13).


One consideration you may have is duct length and location of unit.


I put mine in the basement plant room so have some very long and very short runs. This made balancing a challenge but I got there in the end - only had the ceiling plenums as a means of adjustment. On the up side the intake/extract to exterior are quite short (good given they are 180mm steel, closer to 250mm when insulated). The manifolds were 14 port each (one supply, one extract) so more or less filled.


Have you thought as to where you will locate yours and how to manage the not inconsiderate ducting and manifold - while the ducts are flexible, it can get pretty congested when they all come together and tight bends will reduce airflow.

Edited by Bitpipe
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Thanks guys. We've had a few conflicting quotes back regarding our requirements - hence me posing the question about system size.


I have already contacted BPC too, but I'm still waiting for them to get back to me. EpicAir are keen to sell me two Q600 Zehnders which is way over our budget (whilst even two systems would only just be able to cope according to their specs); whilst the company installing our Air Source Heat pump is recommending a Daikin commercial unit at half the price. 


Some really helpful info there Bitpipe...thanks for that!! To answer your question regarding location. We've got a similar approach to you and will be placing it in a designated plant room that is directly below our single-storey utility area. If we got for one of the commercial systems we plan on having the manifold in the plant room too to convert the 250mm ducting into 90mm ducting. We've deliberately left out some blocks in the beam and block floor for the ducting to go straight up into the utility where it can then quickly access the roof, as well as allow the pipework to gain access to the rest of the house. 

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