MVHR Basics

[Sjk]

First of all, new build, not a PH. Around 130m2 over 2.5 floors. 

 

I have seen a lot of systems have one vent that draws the air from the kitchen, loos/bathrooms etc and blows air into the bedrooms and living rooms. 

 

Is this “best”?

 

I imagined there would be a lot more vents...

 

Also is there a decent slimline/small system?

[Mr Punter]

Normally it is one vent per room. Some systems have a manifold and smaller ducting.

[Sjk]

I was surprised there was only an extract in the bathroom, if the door is closed the air needs to come from somewhere right?

[Jeremy Harris]

The normal arrangement is to install extracts in bathrooms, WCs, the kitchen, and utility room and fit fresh air supply terminals in all the living rooms and bedrooms.  Air flows from room to room via larger than normal gaps left under all the doors.

[Sjk]

5 minutes ago, JSHarris said:

The normal arrangement is to install extracts in bathrooms, WCs, the kitchen, and utility room and fit fresh air supply terminals in all the living rooms and bedrooms.  Air flows from room to room via larger than normal gaps left under all the doors.

 

Ah, for sound insulation I was going to have air tight doors.

[Jeremy Harris]

5 minutes ago, Sjk said:

 

Ah, for sound insulation I was going to have air tight doors.

 

As an alternative you can fit offset ducts through connecting walls.  We have ~8mm gaps under the doors and don't find that there's a sound transmission problem, though.

[Sjk]

Do you not find it draughty? 

 

Im wondering if it would be better to have an input and output in the bathroom etc. But that might mean there is a mass of piping etc 

[Jeremy Harris]

2 minutes ago, Sjk said:

Do you not find it draughty? 

 

Im wondering if it would be better to have an input and output in the bathroom etc. But that might mean there is a mass of piping etc 

 

Not at all, the airflow rate from MVHR is really low, barely perceptible if you put your hand over a terminal.

 

It's not a good idea at all to fit fresh air supplies and extracts in the same room, as ventilation would be very uneven and heat recovery would be pretty poor, I think.

[Sjk]

Okay thanks. 

 

Still a shame as mucks with my sound insulation plans 

[PeterW]

3 minutes ago, Sjk said:

Okay thanks. 

 

Still a shame as mucks with my sound insulation plans 

 

What sound insulation are you trying to achieve...?? A solid sealed door may actually transmit sound not block it - MVHR helps where you have the flow between pairs of rooms such as an en-suite into a bedroom etc. 

[Sjk]

A sound engineer has said a sealed doorway will reduce noise travel. 

 

Wonder if it a sound maze coupled with wall vents could be the solution. 

[PeterW]

23 minutes ago, Sjk said:

A sound engineer has said a sealed doorway will reduce noise travel. 

 

Wonder if it a sound maze coupled with wall vents could be the solution. 

 

Sorry - what noise ..??! That’s my question. 

 

If its to stop the sound of someone snoring, the materials need to be different to that of a higher pitched whine for example from machinery. 

 

@Moonshine didn’t you post something about sound absorbtion..?

[Jeremy Harris]

FWIW our house could potentially be really bad from a noise transmission perspective, as we have hard flooring everywhere and a very tall (~6m high) central hall that has doors off the lading directly to the bedrooms.  In practice there's very little noise transmission at all; the TV or stereo can be on in the living room and you can't hear it at all in the bedrooms above, and that's with ~8mm gaps under all the doors.

[MJNewton]

2 hours ago, JSHarris said:

It's not a good idea at all to fit fresh air supplies and extracts in the same room, as ventilation would be very uneven and heat recovery would be pretty poor, I think.

 

Not wishing to hijack the OP's thread but what about large open plan (shared) spaces e.g. kitchen-diner-lounge type layouts? Or would that be more of a case where one might just have to compromise, depending on the layout (e.g. if the kitchen is closest to the door)?

Edited February 13, 2019 by MJNewton

[Jeremy Harris]

If it's a big enough room, then just fit the extract(s) nearest the sources of smells/water vapour and the fresh air terminal(s) as far away as possible at the "living space" end.

[MJNewton]

Thanks, that's what I was thinking (and planning, as this is a situation we're in).

 

Apologies Sjk for that temporary diversion.

Edited February 13, 2019 by MJNewton

[Moonshine]

1 hour ago, PeterW said:

 

Sorry - what noise ..??! That’s my question. 

 

If its to stop the sound of someone snoring, the materials need to be different to that of a higher pitched whine for example from machinery. 

 

@Moonshine didn’t you post something about sound absorbtion..?

 

Sealed doors in internal room? What's the issue?

[Moonshine]

2 hours ago, Sjk said:

A sound engineer has said a sealed doorway will reduce noise travel. 

 

Wonder if it a sound maze coupled with wall vents could be the solution. 

 

A sealed solid core door, with a threshold seal will provide good sound insulation, but the same without the threshold seal wont be that much of a degregation acoustically, but probably will give enough of a gap for air ventilation.

[Gone West]

13 hours ago, JSHarris said:

It's not a good idea at all to fit fresh air supplies and extracts in the same room, as ventilation would be very uneven and heat recovery would be pretty poor, I think.

That is exactly what we have in our kitchen/diner with an extract at the cooking end and a supply at the eating end. It seems to work without any problems. We did run the idea past ADM Systems before we decided to use it and they were quite happy.

[lizzie]

I have an open plan living/kitchen/dining space approx 15m long, 6m at its widest and 3 m at its narrowest.  I have 2 extracts in the kitchen area and two fresh air inlets in the living area.  It was designed by mvhr suppliers that way, works well enough.

 

On the gap under the doors I thought there was some building reg that gave a minimum for the gap, bigger than normal for air circulation, can’t find the relevant reg at mo sorry.

[Jeremy Harris]

26 minutes ago, PeterStarck said:

That is exactly what we have in our kitchen/diner with an extract at the cooking end and a supply at the eating end. It seems to work without any problems. We did run the idea past ADM Systems before we decided to use it and they were quite happy.

 

3 minutes ago, lizzie said:

I have an open plan living/kitchen/dining space approx 15m long, 6m at its widest and 3 m at its narrowest.  I have 2 extracts in the kitchen area and two fresh air inlets in the living area.  It was designed by mvhr suppliers that way, works well enough.

 

I did also post that this would probably be OK in a bigger room:

 

11 hours ago, JSHarris said:

If it's a big enough room, then just fit the extract(s) nearest the sources of smells/water vapour and the fresh air terminal(s) as far away as possible at the "living space" end.

 

[Bitpipe]

10 hours ago, Moonshine said:

 

A sealed solid core door, with a threshold seal will provide good sound insulation, but the same without the threshold seal wont be that much of a degregation acoustically, but probably will give enough of a gap for air ventilation.

 

We have FD30 fire doors on all rooms that open onto our hall (with fire strip and stops) - they're mostly 820mm wide so the MVHR airgap is only 7mm. We used blue plasterboard on the basement and ground floor ceiling and around the downstairs WC - usual rockwool in the stud cavities etc. Hard floors throughout.

 

Can't say there is much noise issue, thumps and bumps from upstairs are noticeable but our teenage son plays electric guitar in the basement and it's not noticeable unless really cranked up  

 

One of the old eBuild stalwarts Wittenham (Oxford based, did his MBC house around the same time as Jeremy) spent a ton on proper soundproofing technology - decoupled walls, rubber floor mats etc.

 

It didn't work.

 

IRC, he said that low frequency sounds are very hard to prevent.

[Bitpipe]

24 minutes ago, lizzie said:

I have an open plan living/kitchen/dining space approx 15m long, 6m at its widest and 3 m at its narrowest.  I have 2 extracts in the kitchen area and two fresh air inlets in the living area.  It was designed by mvhr suppliers that way, works well enough.

 

On the gap under the doors I thought there was some building reg that gave a minimum for the gap, bigger than normal for air circulation, can’t find the relevant reg at mo sorry.

 

I think it's 76mm2 so 10mm for a regular sized door, less for wider doors.

[Jeremy Harris]

35 minutes ago, Bitpipe said:

 

I think it's 76mm2 so 10mm for a regular sized door, less for wider doors.

 

I make the CSA of a 10mm gap under a 760mm wide door 7600mm², which at the maximum allowable flow velocity in terms of flow noise of around 2.5m/s, gives a flow rate of 19 l/s, which is pretty high.  Background ventilation flow rates under doors are not likely to exceed around 8 to 10l/s I'd have thought.

[Bitpipe]

4 minutes ago, JSHarris said:

 

I make the CSA of a 10mm gap under a 760mm wide door 7600mm², which at the maximum allowable flow velocity in terms of flow noise of around 2.5m/s, gives a flow rate of 19 l/s, which is pretty high.  Background ventilation flow rates under doors are not likely to exceed around 8 to 10l/s I'd have thought.

 

I was only 10³ out