Kitchen extraction externally ducted and MVHR

[Stonehouse]

Now this might sound like a contradiction! 
 

I’m planning a TF house new build with MVHR. Air tightness as low as possible (not passive house level though but under 3)

 

We will have an open plan kitchen 7x7m with a vented downdraft hob. We cook with lots of spices, stir fries, curries and smoky steaks etc 

 

Options are 

1. Recirculating vented Hob. This would maintain heat, but would food smells still linger in an open plan area or would the MVHR assist in extracting and bringing fresh warmed air in?

 

2. Externally extracted vented hob. Will this be better to remove cooking smells compared to recirculating. Although during cooking warm air will be externally extracted. But if this is only an hour for example will it make a difference in the grand scheme of things. 
 

 

 

 

[G and J]

30 minutes ago, Stonehouse said:

Now this might sound like a contradiction! 
 

I’m planning a TF house new build with MVHR. Air tightness as low as possible (not passive house level though but under 3)

 

We will have an open plan kitchen 7x7m with a vented downdraft hob. We cook with lots of spices, stir fries, curries and smoky steaks etc 

 

Options are 

1. Recirculating vented Hob. This would maintain heat, but would food smells still linger in an open plan area or would the MVHR assist in extracting and bringing fresh warmed air in?

 

2. Externally extracted vented hob. Will this be better to remove cooking smells compared to recirculating. Although during cooking warm air will be externally extracted. But if this is only an hour for example will it make a difference in the grand scheme of things. 
 

 

 

 

Option 3, treble MVHR extract vents over stinky bit?

 

Option 4, cook stinky stuff in utility room, (trendily renamed ‘spice kitchen’) and open the window….

 

I'm building in option 5, cook stinky stuff in spice kitchen (see above) and have a closable inlet and extract just for that room.

[JohnMo]

10 minutes ago, G and J said:

Option 3, treble MVHR extract vents over stinky bit?

Last thing you want, is loads of grease clogging your vent ducts. Put the MVHR on the opposite side of the room.

 

We did Indian at the weekend, recycling hood, with carbon filter (not even certain it got switched on for long). MVHR extract about 4m from hob did a fine job of containing nearly all smells.

 

Not sure you need 3, 4 or 5.

[dpmiller]

purists be damned, I just extract for the short period that the wok is a-smokin.

[Nick Laslett]

8 hours ago, Stonehouse said:

Now this might sound like a contradiction! 
 

I’m planning a TF house new build with MVHR. Air tightness as low as possible (not passive house level though but under 3)

 

We will have an open plan kitchen 7x7m with a vented downdraft hob. We cook with lots of spices, stir fries, curries and smoky steaks etc 

 

Options are 

1. Recirculating vented Hob. This would maintain heat, but would food smells still linger in an open plan area or would the MVHR assist in extracting and bringing fresh warmed air in?

 

2. Externally extracted vented hob. Will this be better to remove cooking smells compared to recirculating. Although during cooking warm air will be externally extracted. But if this is only an hour for example will it make a difference in the grand scheme of things. 
 

 

 

 

This is a well warn discussion on BuildHub, you could call it a hardy perennial. Nothing wrong with recirculating hood, but you can extract to the outside as long as the vent has an air tight seal. There is a balance issue when doing this, but might not be significant enough to cause problems. If using a recirculating hood, you can put a filter on the nearest extract plenum. Again some installs have filters on all extract plenums. 
 

As with any thread on BuildHub, it is a lottery whether you will get a good community response and a plurality of views. Here is a link to a recent previous discussion on this topic.  Also here is the passive house guide on the topic:

 

https://passiv.de/downloads/05_extractor_hoods_guideline.pdf

 

* Edit: I notice that the topics are in two different parts of the forum, part of the joy of BuildHub is the complexity of forum structure, some topics have multiple potential homes, easy to miss. 

Edited December 5 by Nick Laslett

[Sparrowhawk]

For those who extract to the outside, it would be helpful if you detail how you make the external vent airtight when not in use.

And tell us if you did your airtightness tests with this taped over or also tested with it in its 'closed' position to confirm how airtight it is.

 

A couple of options have been mentioned in threads but not all in one place, and it'd be helpful to group the options together.

 

[Nick Laslett]

56 minutes ago, Sparrowhawk said:

For those who extract to the outside, it would be helpful if you detail how you make the external vent airtight when not in use.

And tell us if you did your airtightness tests with this taped over or also tested with it in its 'closed' position to confirm how airtight it is.

 

A couple of options have been mentioned in threads but not all in one place, and it'd be helpful to group the options together.

 

I’m actually getting very close to my air test. Early January, hopefully. 
 

The solution I used is no longer sold into the UK market, it is from Germany. We wanted a very quiet cooker extractor as we have an open plan kitchen. We went with the Berbel extractor and the Wall Box accessory, which connects to the extractor and opens the vent automatically using a motor. Spec says >40PA for the wall box opening. 
 

https://www.berbel.uk/extractor-hoods/accessories/exhaust-accessories/wall-box/

 

When I looked more recently, I saw there was another product now on the UK market. 
 

https://luxairhoods.com/Cooker-Hood-Ducting-150mm/cooker-hoods-outside-vents-grilles-external/Airtight-Ducting-System-Kits?srsltid=AfmBOor176UUNI2MTtZdpI9A2SZBl2x7Bir3KZKSyicPgC3GHIE6BwXW

 

The other area that is worth exploring is butterfly valves in the duct. 
 

https://quiet-vent.com/products/dampers/quiet-vent-motorised-circular-damper/

 

I assume that MVHR professionals will be familiar with other options. The Passive House Institute guideline I linked earlier covers the design requirements for extracting to the outside. 
 

This is the only PHI approved product on their database. 
 

https://naber.com/media/52/7b/ce/1688370360/NABER-Compair-Bixo-Broschuere_EN.pdf

 

Like a lot of house design choices this forum in very pro recirculating hoods and there is nothing wrong with that approach, but a bit like asking for recommendations for oil fired boilers, I would guess must members wouldn’t be leaping to give advice. 

[Mike]

On 04/12/2024 at 23:16, Stonehouse said:

1. Recirculating vented

This is my preference, however, as @JohnMo says, you don't want grease in the the MVHR. So it's worth knowing that there is a European 'Grease Filtering Effectiveness' classification that requires hoods to be rated from G (<=45% effective as removing grease) to A (>95% effective). Manufacturers tend to keep quiet about it, but it's usually buried in the specs. Bosch, Neff, Miel & Berbel all have B rated models (>85% effective), but Ikea has the only A rated that I've come across so far.

[Stonehouse]

Thanks for the comments and link to the other thread which was useful albeit brief air frier chat 😂 

 

@Nick LaslettThe passive house document is a good read which explains it well as is the blog with its views. Thanks got the links to the extracting options. How easy is it to access these things if the motor fails? What was the reason it decided to extract out?

 

 It’s important to get views who have lived experiences of both options. Sounds like the recirculating option works well for you @JohnMo
 

interested to know @dpmiller how you have found extracting outside and if there has been a issue with heating etc

 

 

[dpmiller]

7 minutes ago, Stonehouse said:

interested to know @dpmiller how you have found extracting outside and if there has been a issue with heating etc

Ive just got a gravity flap  (with rubber seals) in the pipe up from the hood and it seals fine but can occasionally rattle in strong winds from a certain direction. I really only use the extractor when frying/ stirfrying as generally the MVHR deals with a wee bit of steam fine. I've considered adding either a motorised damper or a Thermobox but have never got any farther than that

 

The MVHR is set up for slight positive pressure as there's a woodstove at the other end of the house. Only if the cooker hood is turned right up to boost does it actually attempt to depressureise the house, on all other speeds the extra air just freewheels the MVHR's supply fan as far as I can tell