MVHR Design And Install

[Adrock]

Another thread to add to the multitude! 

 

I need a design for my house, I'm happy with installation and construction but I'll need duct sizes and some direction to how I'll get over a couple of tight spots where I have under 90mm from bottom of steel to finished ceiling.

 

I contacted CVC systems over a week ago and the initial emails were very responsive, but nothing at all last week. My situation, which I was very clear about, probably contributed to it. I won't be in a position to purchase or install the MVHR for probably a year or so, but I need the duct installed in the next few weeks.

 

Are on you lovely folk able to point me in the direction of a decent resource to enable progression of the design?

[BotusBuild]

Have you tried BPC Ventilcation? https://bpcventilation.com/

 

Send them your plans, they come back with a design. For a fee I think they then provide you with flow rates etc.

 

I used them for layout design and choice of unit. We had a few back and forth discussions about why certain elements of their layout would not work, but we did arrive at a final design. It was based on using distribution boxes and semi rigid ducting.

[Nickfromwales]

4 hours ago, Adrock said:

Another thread to add to the multitude! 

 

I need a design for my house, I'm happy with installation and construction but I'll need duct sizes and some direction to how I'll get over a couple of tight spots where I have under 90mm from bottom of steel to finished ceiling.

 

I contacted CVC systems over a week ago and the initial emails were very responsive, but nothing at all last week. My situation, which I was very clear about, probably contributed to it. I won't be in a position to purchase or install the MVHR for probably a year or so, but I need the duct installed in the next few weeks.

 

Are on you lovely folk able to point me in the direction of a decent resource to enable progression of the design?

I know CVC are crazy busy atm. 
 

Just swap from 92mm round to ‘oval’ (rectangular) duct to pass the steel and then covert back to round. Done it plenty of times.

Some examples of my MVHR installs…

 

 

 

 

 

 

 

 

Hope these examples help. 👍

[Adrock]

Cheers @Nickfromwales.

 

I'll chase them tomorrow and if they can't accommodate me I'll get onto BPC and see if they can help. 

 

I'm happy to pay for a design if it helps.

[Nickfromwales]

12 minutes ago, Adrock said:

Cheers @Nickfromwales.

 

I'll chase them tomorrow and if they can't accommodate me I'll get onto BPC and see if they can help. 

 

I'm happy to pay for a design if it helps.

They usually do a design / supply / commission package for self builders who want to DIY, so just ask for a rudimentary layout / design; all you need is the number of ducts and location of terminals, but it’s pretty simple to work out.

 

If you have any long runs to bedrooms, double up on the duct to quieten the airflow as much as possible. 

[Indy]

In the process of using Heat Space and Light. Design and supply of parts through them, installation done by the builder or me, and then final commissioning by HSL to get it signed off. Pretty happy with the service so far, at the design finalised stage. 

[Adrock]

Thanks, I'll look them up. I'm in the process of doing a whole house renovation and I suspect I won't be ready for everything for a very good while. 

 

I might split the the basement and ground floor to get something on the go but that will still be a year in the making.

[BotusBuild]

Its worth getting the design earlier rather than close to when you think you need it, in order to ensure that the various parts will fit where expected. 

 

You may be able to make adjustments to other works to make the MVHR ducting fit better

[JohnMo]

13 hours ago, Adrock said:

whole house renovation

Is the plan to make it airtight - if not don't bother with MVHR. You could instead install a demand based MEV or dMEV system, which responds to humidity with automatic fan speed regulation and trickle vents that open and close to room humidity. I would be doing that even if I was going airtight! Super simple, limited heat losses, cheap enough to do.

[Alan Ambrose]

>>> I need a design for my house

 

There's a spreadsheet on BH somewhere which I've used, also manufacturers have their own free calculators. My BC was happy with the latter. Not rocket surgery as they say.

[Adrock]

6 hours ago, JohnMo said:

Is the plan to make it airtight - if not don't bother with MVHR. You could instead install a demand based MEV or dMEV system, which responds to humidity with automatic fan speed regulation and trickle vents that open and close to room humidity. I would be doing that even if I was going airtight! Super simple, limited heat losses, cheap enough to do.

 

Yes, airtightness is a feature of what I'm planning. Everything to do date has been detailed for a high degree of airtightness.

 

The house is of solid masonry construction and will be externally insulated in future. Hopefully that'll afford me the opportunity to get as airtight as possible.

[Adrock]

6 hours ago, Alan Ambrose said:

>>> I need a design for my house

 

There's a spreadsheet on BH somewhere which I've used, also manufacturers have their own free calculators. My BC was happy with the latter. Not rocket surgery as they say.

 

Thanks, any recommendations? I suppose my main concern is the placement of the room outlets, are there any specific considerations I should be mindful of?

[Nickfromwales]

2 hours ago, Adrock said:

 

Yes, airtightness is a feature of what I'm planning. Everything to do date has been detailed for a high degree of airtightness.

 

The house is of solid masonry construction and will be externally insulated in future. Hopefully that'll afford me the opportunity to get as airtight as possible.

External insulation will offer zilch in terms of airtightness, if you have a cavity. 

[JohnMo]

2 hours ago, Adrock said:

 

Thanks, any recommendations? I suppose my main concern is the placement of the room outlets, are there any specific considerations I should be mindful of?

I would look at coanda supply and extract terminals, they will push air across the ceiling/room, and extract will suck air across the room, so makes placement way easier and duct runs way easier. 

Brink-Multi-Air-Supply-systeem-Leaflet_4388762584830.pdf

You can do something like this also, so you are basically supplying air to central location and only extracting from wet rooms

 

[Mike]

9 hours ago, Alan Ambrose said:

There's a spreadsheet on BH somewhere which I've used

This one, perhaps?

 

[JohnMo]

35 minutes ago, Mike said:

This one, perhaps?

Not really sure you need to be that complicated.

[Alan Ambrose]

The spreadsheet is pretty simple really. The other option I used for comparison and the one the BC preferred, presumably because they were independent calcs, was the free online Ubbink ‘Aerflux Project Report‘:

 

https://www.ubbink.com/int/advice-service/aerflux-configurator/

 

[Alan Ambrose]

This kind of thing. It also generates a list of Ubbink components to buy (surprise!) but the calcs apply to any manufacturer's duct of the same approx diameter.

 

 

Edited 14 hours ago by Alan Ambrose

[Adrock]

On 11/05/2026 at 20:13, Nickfromwales said:

External insulation will offer zilch in terms of airtightness, if you have a cavity. 

 

Yeah, I'll need to be looking at lots of airtightness details internally if I can't do anything externally. I'm not doing this on the cheap so it's definitely going to be airtight when I'm finished.

[Adrock]

On 11/05/2026 at 20:25, JohnMo said:

I would look at coanda supply and extract terminals, they will push air across the ceiling/room, and extract will suck air across the room, so makes placement way easier and duct runs way easier. 

Brink-Multi-Air-Supply-systeem-Leaflet_4388762584830.pdf 385.38 kB · 18 downloads

You can do something like this also, so you are basically supplying air to central location and only extracting from wet rooms

 

 

Cheers, I'll take a look at that. I got a quote back today, seems expensive.

[JohnMo]

3 minutes ago, Adrock said:

 

Cheers, I'll take a look at that. I got a quote back today, seems expensive.

My first quote 6 years ago was £10k - bonkers. Ended up DIY and spend around £2k

[Nickfromwales]

51 minutes ago, Adrock said:

 

Yeah, I'll need to be looking at lots of airtightness details internally if I can't do anything externally. I'm not doing this on the cheap so it's definitely going to be airtight when I'm finished.

Are you able to use AeroBarier? just needs the house pretty empty and a lot of covering up furniture, and robust masking off all floors and flat surfaces. Got a masonry refurb down to sub 0.2 ACH before xmas!!!

[Adrock]

It's a shame I'm living in the bloody thing, I'd love to be able to use aerobarrier

 

I'm going to have to try and do it on a floor by floor basis, I think. Once the basement is done I'll move onto the ground floor and strip it all back, that might provide an opportunity to do what I can do, test and then if needed, get aerobarrier in to do their magic.

[Adrock]

1 hour ago, JohnMo said:

My first quote 6 years ago was £10k - bonkers. Ended up DIY and spend around £2k

 

Materials are £10k and install £6k, the house will be just over 200m2 across four levels one day. Plenty of work to get there though.

[JohnMo]

3 minutes ago, Adrock said:

 

Materials are £10k and install £6k, the house will be just over 200m2 across four levels one day. Plenty of work to get there though.

Ours is nearly 200m² on a single floor. If you are looking at anything near that cost I won't thinking again. If our target airtightness had not demanded it (Scottish building regs) I would have gone dMEV or MEV. Very little in it, heat loss wise.

 

dMEV demand based system 

Wet rooms, Greenwood CV2 one in each room including kitchen. Or central MEV with humidity activated terminals and constant pressure fan in MEV unit. Automatically and smartly do boost it needed, run at a very low flow all the time. From eBay look at around £40 each, for Greenwood CV2 fans, almost silent, draw almost no electricity, zero maintenance. No trickle vents in wet rooms. 

 

Dry rooms, trickle vents that is humidity activated (can include acoustic damping if you need) around £60 to £120 each. Can be through wall or in window.

 

How it works, day time, bedrooms not used, trickle vents almost fully closed. Downstairs rooms have people so the vents start to open in response to rising humidity, fans draw the air across the room, through corridors and out the house. At night the effect swop, now bedroom trickle vents open and downs close. No-one in house, all trickle vents go to min opening.

 

As with MVHR you have internal doors under cut around 6 to 10mm