MVHR duct strategy for a kitchen, one or two terminals?

[Seeoda]

Hi all,

 

In the ductwork design, a lot of a layout is determined by the specifics of a house, which has to be figured out case-by-case basis. I understand that it isn't possible to generalise too much, but, is there a general view on ventilation for a kitchen in a typical-sized house? Some kitchens are only built with a single terminal, extract only, but is an input also best practice? I am thinking about this for a scheme house that is rather small and narrow, but three story and some rooms seem to have a worrying loss of pressure, including the ground floor. I guess having an input and extra in one room reduces the risk of sticking doors too. The MHRV unit is in the attic. So I am thinking about my options.

[Dan F]

6 minutes ago, Seeoda said:

Hi all,

 

In the ductwork design, a lot of a layout is determined by the specifics of a house, which has to be figured out case-by-case basis. I understand that it isn't possible to generalise too much, but, is there a general view on ventilation for a kitchen in a typical-sized house? Some kitchens are only built with a single terminal, extract only, but is an input also best practice? I am thinking about this for a scheme house that is rather small and narrow, but three story and some rooms seem to have a worrying loss of pressure, including the ground floor. I guess having an input and extra in one room reduces the risk of sticking doors too. The MHRV unit is in the attic. So I am thinking about my options.

Depends on size and layout of your kitchen.  Ours has 2 extracts over the kitchen island (to get require extract flow rate) and a single supply in a connected breakast area.

 

8 minutes ago, Seeoda said:

I guess having an input and extra in one room reduces the risk of sticking doors too.

Most MVHR designers will calcualated required door undercuts based on flow required between rooms.

[JohnMo]

Building standards require a 10mm undercut above floor coverings, to allow all doors to be closed and get the required air movement around the house.

 

Generally you only extract from wet rooms and kitchens.  Supply goes to all dry rooms.  In a dry room air enters the room away from a door or opening window, flow across the room out/under the door either to an adjacent wet room or down the corridor to a wet room.  This way all the air in the property is replaced.  

 

Having a supply and extract in the same room, means the air flow path misses most the house just goes direct from A to B.

 

Below is a guide to air flow rates by different countries in the UK and passivhaus

 

[Adsibob]

4 minutes ago, JohnMo said:

Building standards require a 10mm undercut above floor coverings, to allow all doors to be closed and get the required air movement around the house.

Not sure that is quite right. It depends on the width of door. Required area of under-door opening is 7600mm2. So 10mm works for a 760mm wide doorway, but you can get away with a shorter gap if you have a wider door.

[JohnMo]

You are correct Scottish building regs actually say 8000mm2, so a 760mm door would require 10.5mm, an 838mm door would need 9.5mm and English regs would require 10 or 9mm.

 

[joe90]

In my large kitchen diner I had both an extract (kitchen end) and supply (dining end) and works well

[Adsibob]

11 minutes ago, JohnMo said:

You are correct Scottish building regs actually say 8000mm2, so a 760mm door would require 10.5mm, an 838mm door would need 9.5mm and English regs would require 10 or 9mm.

 

I didn’t like the look of such big gaps, so went with the widest doors I could fit and went down to 7mm or 8mm. On the 7mm gaps, I’m probably a bit short of the 7600mm2 sq requirement but my MVHR designer said it wouldn’t matter, and he was right.