MVHR Grill placement for supply / extract

[Wookie_73]

Hi all.

 

I am in the midst of designing my MVHR system for my house I am renovating.

I am happy with he design on the whole but I have one room that I am not sure about the vent placement, indeed even if I should have supply vent in that room at all.

I have attached my proposed layout / vent placements for the first and ground floor. Any comments are more than welcome.

I have also attached a ground floor layout marked up with a 3.5m distance between a supply and extract vent.

My question is this a great enough distance to prevent short circuiting?

Also do I even really need this vent? I added it to help bring down the air velocity in the main air supply vent on the ground floor.

I realise the ducting takes a convoluted route on the ground floor. This is because I am dropping the ceiling level every where on the ground floor by around 100mm to accommodate services except in the hallway.

All vents located near corners are 350mm away from walls.

 

Also would you normally put the vent in the bathroom above the bath / shower area?

 

Thanks for any advice.

Dave

 

EDITED TO REMOVE PLANS, PLEASE SEE POST FURTHER DOWN FOR PLANS

 

Edited Sunday at 22:39 by Nickfromwales
Plans removed to anonymise project

[Nickfromwales]

Hi. 
Firstly, you’ve left the address on public view, do you want to upload anonymised versions instead? 
 

Secondly, are you making the property airtight and are testing it with an aim to get a target result? Eg <1 ACH. 

[JohnMo]

16 minutes ago, Wookie_73 said:

would you normally put the vent in the bathroom above the bath / shower area

Mine are directly over baths or shower areas. But other will say the complete opposite, so make your choice.

 

Difficult to tell from the drawing is it one large kitchen diner? You seem to have 2x extract one over island and other over sink? If one room one extract is fine, but not above hob, as you will fill the system with grease.

[Mike]

8 hours ago, Wookie_73 said:

All vents located near corners are 350mm away from walls.

I wouldn't put the ceiling supply vents right in the room corners & so close to the walls, particularly in the bedrooms. Many such vents use the Coanda effect (which is recommended) so that the air disperses evenly across the ceiling. However, if a wall is in the way, the air will be deflected down the wall and may cause an unwanted draft; from memory 750mm is the recommended minimum distance from a wall. Zehnder's Luna S (and probably others) have an optional deflector that can be inserted to get around that.

 

8 hours ago, Wookie_73 said:

I have also attached a ground floor layout marked up with a 3.5m distance between a supply and extract vent.

My question is this a great enough distance to prevent short circuiting?

Also do I even really need this vent? I added it to help bring down the air velocity in the main air supply vent on the ground floor.

What @JohnMo says. Just add a double pipe to the extract over the sink.

 

7 hours ago, Wookie_73 said:

Also would you normally put the vent in the bathroom above the bath / shower area?

Zehnder's advice is to place the extract near a shower, but not within / over it.

 

[Wookie_73]

On 24/01/2025 at 12:48, Nickfromwales said:

Hi. 
Firstly, you’ve left the address on public view, do you want to upload anonymised versions instead? 
 

Secondly, are you making the property airtight and are testing it with an aim to get a target result? Eg <1 ACH. 

Yes I would like to remove the address, silly mistake on my part. How do I edit my original post?

 

Yes I am trying to make the property as airtight as I can. It is a 1930's house so there has / is a lot of sealing done or to be done.

[Wookie_73]

On 24/01/2025 at 12:49, JohnMo said:

Mine are directly over baths or shower areas. But other will say the complete opposite, so make your choice.

 

Difficult to tell from the drawing is it one large kitchen diner? You seem to have 2x extract one over island and other over sink? If one room one extract is fine, but not above hob, as you will fill the system with grease.

Yes it is one large kitchen diner.

The extract over the island is close to where the hob is. I could ditch this and just have one extract.

[Nickfromwales]

20 minutes ago, Wookie_73 said:

Yes I would like to remove the address, silly mistake on my part. How do I edit my original post?

Just post the plans again in your next post, please. I have removed them from the original, as it's the documents themselves that need editing before posting vs the post  

[Wookie_73]

On 24/01/2025 at 21:16, Mike said:

I wouldn't put the ceiling supply vents right in the room corners & so close to the walls, particularly in the bedrooms. Many such vents use the Coanda effect (which is recommended) so that the air disperses evenly across the ceiling. However, if a wall is in the way, the air will be deflected down the wall and may cause an unwanted draft; from memory 750mm is the recommended minimum distance from a wall. Zehnder's Luna S (and probably others) have an optional deflector that can be inserted to get around that.

 

What @JohnMo says. Just add a double pipe to the extract over the sink.

 

Zehnder's advice is to place the extract near a shower, but not within / over it.

 

I was looking at the Zehnder ComfoValve Luna S125 for the supply. The recommended minimum distance from corners is 350mm in there documentation. They have what looks like a foam segment that you put in to slow the flow pointing toward the corner.

This is where the 350mm came from.

I quite like the look of these valves and they seem affordable.

However what I would like is a plaster in type diffuser so I don't have anything protruding down from the ceiling but I cant seem to find any that don’t cost stupid money. Any recommendations?

[Wookie_73]

11 minutes ago, Nickfromwales said:

Just post the plans again in your next post, please. I have removed them from the original, as it's the documents themselves that need editing before posting vs the post  

Thanks Nick

MVHR Layout First.pdf MVHR Layout Ground - With notes.pdf MVHR Layout Ground.pdf

[Mike]

22 minutes ago, Wookie_73 said:

I was looking at the Zehnder ComfoValve Luna S125 for the supply. The recommended minimum distance from corners is 350mm in there documentation.

I'm using the same model and that is indeed their minimum distance. However I've seen it recommended that Coanda-effect vents should be >750mm away from walls, though I can't give you a reference for that. But since they disperse the air across the ceiling in all directions, there is no need to squash them in a corner.

 

23 minutes ago, Wookie_73 said:

what I would like is a plaster in type diffuser so I don't have anything protruding down from the ceiling but I cant seem to find any that don’t cost stupid money

I'd prefer that in principle too. However if they don't protrude from the ceiling you don't get the Coanda effect; instead the air will blow in whatever downward direction the vent deflectors dictate, albeit gently. That's not a problem if you have space to site them away from where they may cause a draft, but not so good in a smallish room where you don't have that freedom.

 

At lest the Zehnder Luna protrudes less than most and they look reasonably good.

[Nickfromwales]

11 hours ago, Wookie_73 said:

However what I would like is a plaster in type diffuser so I don't have anything protruding down from the ceiling but I cant seem to find any that don’t cost stupid money. Any recommendations?

What do you think is stupid money? 
 

 

To not have my ceiling cluttered with the usual ‘utilitarian’ looking air valves I’d happily pay these prices, especially in day rooms such as kitchen diners and living rooms etc, but even more so in a bedroom where the linear can be lost over a window etc. 
 

Why scrimp on something that you’ll be looking at all day every day? 
 

Place them strategically and design the layout sympathetically and you’ll have adequate, even, quiet airflow through any space.

 

The projectile effect, a benefit from the Coanda ethos is a bit OTT here, usually reserved for long throw instances like commercial and public open spaces with vents on the vertical facades vs a small ish residential dwelling   

 

No need to go to all this hassle, and I think there’s a bit of overthinking going on here tbh. 

[Wookie_73]

They look good.

I will have a look at that website. I was looking at ones like the round diffuser but they were over £150.

£80 seems more acceptable. I totally agree about trying to keep the clutter off the ceiling. If only I could fine smoke alarms that look nice.😂

[MikeSharp01]

We have zender ones fully adjustable flow and don't need any fixing they grip the plenum pipe.

https://www.international.zehnder-systems.com/en/comfortable-indoor-ventilation/products/air-diffusers 

 

[Mike]

11 hours ago, Nickfromwales said:

The projectile effect, a benefit from the Coanda ethos is a bit OTT here, usually reserved for long throw instances like commercial and public open spaces with vents on the vertical facades vs a small ish residential dwelling

Wall-mounted Coanda effect vents are indeed very useful to protect supply air across large spaces.

 

However domestic ceiling mounted Coanda-effect vents have the opposite effect and a different benefit. They're intended to mix the supply air (which will be a few °C colder than the room temperature in winter), with the room air, while the airspeed drops, the two effects combining together to avoid cool drafts. Here's an example in a domestic-sized room using the Zehnder ZSX 125 Coanda-effect diffuser; the colours show airspeed, but if you mentally swap them round (so blue = warmer & yellow = cooler) that would be more-or-less the temperature distribution.

 

 

In a small room, especially a bedroom, where you can't avoid having a vent near a bed, that can be pretty useful.

 

 

[Mike]

7 hours ago, Wookie_73 said:

If only I could fine smoke alarms that look nice.

You won't find flush ones, but those from Cavius are (or at least were when I bought mine) marketed as the World's smallest. Some have optional recessed bases to make them even less prominent.

[Nickfromwales]

Is this actually going to happen with trickle rates? Reasonable to think this would be more relevant when boosting, eg perhaps a good consideration for instances where running the fan speeds up during summer helps attain Part O compliance.

[Nickfromwales]

2 minutes ago, Mike said:

You won't find flush ones, but those from Cavius are (or at least were when I bought mine) marketed as the World's smallest. Some have optional recessed bases to make them even less prominent.

Never seen those before tbh. 

 

Thanks for the link, much appreciated.

[Mike]

3 minutes ago, Nickfromwales said:

Is this actually going to happen with trickle rates?

As you turn down the airflow on a Coanda-effect diffusers the mixing-distance will certainly decrease; no doubt there's a formula out there for that. If you turn down the airflow on a regular diffuser the air will increasingly tend to fall vertically (if it wasn't already being pointing straight down) as cooler air is denser, and you wouldn't want that over (or close-to) a bedhead, for example.

[G and J]

Until this thread we were pretty sold on ergovents, a mix of linear and square ones depending on which room.  It does t take much to worry me lol

[Nickfromwales]

11 hours ago, Mike said:

As you turn down the airflow on a Coanda-effect diffusers the mixing-distance will certainly decrease; no doubt there's a formula out there for that. If you turn down the airflow on a regular diffuser the air will increasingly tend to fall vertically (if it wasn't already being pointing straight down) as cooler air is denser, and you wouldn't want that over (or close-to) a bedhead, for example.

I always aim to put supply vents in the area that is diagonally opposite to the door, eg where the air exits the room.

 

The difference between rooms temp and incoming air temp (fresh supply air from MVHR) is really negligible in real life, so it doesn’t really matter on trickle. The air will mix relatively quickly and be inconsequential by the time it floats its way across the bed head.
 

None of my clients have ever given feedback to the contrary (negative), but if it’s a larger family home with a few bathrooms then boost would need to be factored in as a consideration, at the design phase, to prevent that 30 or 60 min ‘nuisance’.

[Mike]

36 minutes ago, Nickfromwales said:

The difference between rooms temp and incoming air temp (fresh supply air from MVHR) is really negligible in real life, so it doesn’t really matter on trickle.

It will be a few °C in winter.

 

For a real-life example: "In my bedroom the vent is about 0.5m to the side of the bed head and I only notice it on very cold nights." https://forum.buildhub.org.uk/topic/25366-directional-vents-diffusers/#comment-388570

 

[G and J]

41 minutes ago, Nickfromwales said:

I always aim to put supply vents in the area that is diagonally opposite to the door, eg where the air exits the room.

 

The difference between rooms temp and incoming air temp (fresh supply air from MVHR) is really negligible in real life, so it doesn’t really matter on trickle. The air will mix relatively quickly and be inconsequential by the time it floats its way across the bed head.
 

None of my clients have ever given feedback to the contrary (negative), but if it’s a larger family home with a few bathrooms then boost would need to be factored in as a consideration, at the design phase, to prevent that 30 or 60 min ‘nuisance’.

Oh good.  Ergovents are back on the shopping list then.  There’s only the two of us and I rarely bother to wash anyway (I am a boy, after all), so I won’t be causing boosting too often.  

[Mike]

12 hours ago, G and J said:

Until this thread we were pretty sold on ergovents

I liked the look of them too, but decided against them because of the lack of a Coanda effect and lack of 'safe' placement options in my apartment. If you have larger rooms with have enough space to place them carefully, then they're not likely to be a problem. Though, from memory, I don't thing there's Zhender-type sock filter that you can add to them.

 

Edited Tuesday at 12:16 by Mike

[Wookie_73]

13 hours ago, Mike said:

You won't find flush ones, but those from Cavius are (or at least were when I bought mine) marketed as the World's smallest. Some have optional recessed bases to make them even less prominent.

Thanks for pointing me towards the Cavius smoke detectors. They are just the type of thing I have been looking for.

[Nickfromwales]

40 minutes ago, Mike said:

It will be a few °C in winter.

 

For a real-life example: "In my bedroom the vent is about 0.5m to the side of the bed head and I only notice it on very cold nights." https://forum.buildhub.org.uk/topic/25366-directional-vents-diffusers/#comment-388570

 

Yes, it’s possible to link to adverse examples, but in my M&E designs I mitigate these things out before they become a problem. 
Having these issues afterwards means you either didn’t have an M&E designer or coordinator, or had a poor one.

To have such cold air constantly pumped into your fantastic new home, is rubbish in terms of a result, sorry. 
 

To mitigate that particular issue I “heat” (zap the cold out of) the incoming air; this is done by sending the supply air coming out of the MVHR unit into a heat battery, fed from the ASHP, and then onto the distribution manifold. This had the equal effect in the summer, zapping the heat out (if the HP is in cooling mode).

 

If someone has designed a system that constantly blows cold air onto whilst you lay in your bed at night……👎. 💩.

“Don’t let the door hit you on the ass on the way out”