How close can plenums be to corner of rooms?

[phatboy]

Hi all,

 

Sorry for the basic question, but the answer seems to be missing from the BPC guides and I've only found a few fragments of information online.

 

How close can a plenum be to the corner of a room to work properly.  I've read 50cm somewhere.  Can I be a bit closer if needs be (Ceiling downlights are all roughly 70cm from the corners so I need to work around them as they got there first!) ?

 

For kitchen and bathroom I am going to be fitting them roughly centrally, according to BPC's design.

 

Hopefully once my install is done I can provide advice too 

 

Many thanks

Tim

[Jeremy Harris]

Depends.  Ceiling mounted "mushroom" terminals/air valves (like these: https://cvcdirect.myshopify.com/collections/ceiling-valves/products/conus-airvalve-125mm-1 ) need to be spaced away from walls as they draw, or supply, air around the periphery.  Around 300mm to 500mm is a reasonable spacing from walls.  Non-"mushroom" terminals/air valves, that have a directional front grille (like these: https://cvcdirect.myshopify.com/collections/ceiling-valves/products/turn-airvalve-125mm ) can be fitted close to walls, if ceiling mounted, or can be fitted to walls (we have these in our bedrooms, fitted into walls).

[phatboy]

Thank you very much @JSHarris, very useful and helpful information   I am using the 'mushroom' type

 

I'll consider going a little closer than 50cm in some cases then, to try and balance aesthetics vs function.

 

I wish I'd discovered this forum sooner!

 

Whilst I have you, may I pose another question?

 

My design from BPC has 5 inlet valves, (living room, bedrooms, dining room, and 3 extracts (Kitchen, bathroom and Utiltiy).  The utility has the required 8l/s, however the room is tiny, approx 3.25m3.  Also, this extract has just 1 75mm pipe fitted, maybe as it's almost next to the manifold.

 

- If I was to keep to the 8l/s, should I double up the 75mm pipes to this valve?

- I'd prefer to drop the rate so that I can reduce the door undercut to stop washing machine noise.  Is this a reasonable thing to do?  The room contains a washing machine and condenser dryer only (due to it's size).

 

Sorry if that is worded confusingly, I'd be happy to share my design if you (or someobody else knowledgeable) had time to glance over it?

 

I see BPC get strong reviews here, however I have found the information to be a bit lacking sometimes, despite the kit being excellent.

 

Thanks

Tim

 

[Jeremy Harris]

There's a couple of points worth noting.  The first is that, as mentioned a few times here, the building regs ventilation rates for continuous mechanical ventilation tend to be a lot higher than needed for most well-insulated and sealed houses.  The PH ventilation rate is a better guide, and tends to be a lot lower than that given in Part F.  Also, when calculating rates from Part F, then it's worth noting that usually the whole house ventilation rate exceeds the sum of the minimum extract rates for specific rooms, so although the 6l/s, 8l/s and 13l/s figures for extracts are a useful guide when it comes to getting the ratios right when balancing the system, in practice the whole house ventilation rate may well require a higher overall extract rate in order to comply with the regs.

 

It's well worth running through the requirements in Part F, using your house dimensions, in order to see whether you can just rely on the specified room extract rates, or whether the whole house rate will dominate.

 

Once the MVHR commissioning and balancing has been done and submitted to building control (they may or may not ask for it, though), and been signed off, there's no good reason to maintain the whole house ventilation rate at the level in the regs; often there are significant advantages in turning it down. 

 

The section in building regs that applies is Part F, tables 5.1a and 5.1b, with the associated notes.

 

[ProDave]

The vents that BPC supply come with a few little plastic curve shaped things. They are designed to be inserted as baffles if one side of the vent ends up very close to a wall.

[phatboy]

Thanks @JSHarris.  I have calculated it just now, but based on the regulations in the Jersey Building Control 'Ventilation Rates for Dwellings'.

 

Based upon it being a 3 bedroom property, I would require a rate of 21l/s.  However, the whole house rate based on 0.3l/s per m2 comes out at 28.2l/s, so extremely close to the 29l/s quoted by BPC, based on a kitchen, bathroom and utility room.

 

I never intended to actually run the system at those rates based on what others here have said and experienced.

 

Interestingly, I cannot find anywhere that says I must notify about this work - probably because our rules tend to lag behind the UK a bit!  There are rates that must be acheived in ventillation, but no need to notify when making changes of that type, or so it would seem.

 

Tim!

[phatboy]

@ProDave, I was thinking to use those in one of the bedrooms to direct air away from the bed, I've read about people experiencing 'cold shoulders'.  Equally I will use them if it seems a vent is too close to the wall.

[Jeremy Harris]

Here it seems to be pot luck as to whether building control ask for an MVHR commissioning report or not.  I've heard some here say they didn't need one, I was told I did need to provide one, but I have a very strong suspicion it was just filed without being looked at.  The regs here say that one needs to be produced, and they give a recommended procedure for producing one in a supplementary document (the Domestic Ventilation Compliance Guide: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/456656/domestic_ventilation_compliance_guide_2010.pdf ), yet I rather think this is just ignored by a lot of building control bodies.