Besidethewye

Cooker hood in a passive house

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We have an island that will have an induction hob in it.  Going around the circle of extraction (recirculating rather than venting) and not sure where to stop.

 

The house is passive with MVHR and an extract in the kitchen ceiling about 1.5m to the side of the hob location.  

 

We've mainly had houses with no extract/hood and never worried - but they have always been leaky in comparison (cold and old).  

 

I was going to leave a cable and space in the ceiling so I could fit a ceiling mounted unit if we need it.  But wondering about either a suspended recirculation unit or integrated hob unit with down draught.  

 

I don't want to fill the MVHR up with grease if we can help it - and we don't do a great deal of frying - but someone might or our new diet might switch to chips....

 

We have friends who built a passive house recently - started with no extract but came back to get one - but their MVHR looks a bit odd to me - one vent in the open plan kitchen diner that's maybe 20 feet from the hob (and only one in the whole room - which I assume, but don't know, is extract rather than supply).

 

I am sure this loop has been gone round a few times but couldn't find much with my searching. Appreciate any experience.

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Yes recirculating hood with carbon filter.

 

As well as fitting a cable, but some dwangs (noggins) across the ceiling where it is going so you have something to fix to.

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We have a recirculating extractor hood over the hob, does a good job but does get greasy inside so is cleaned regularly. Vents to ceiling level within the room.

 

The hob sits opposite the wall ovens so in the ceiling mid way between them is a MVHR extract. We have one other in the kitchen for general extract.

 

Our hood did not have the right connections to wire it directly into the MVHR (which does have a cooker hood boost terminal), we could have put a current sensor on the feed to trigger it but tbh the built in humidity sensor generally kicks in or I just hit the boost button in the utility.

 

I've popped off the cover of that MVHR extract and it's not at all greasy inside but is a bit dusty - more so than the bathroom extracts but I expect that is because there are in a damper and therefore less dusty environment. 

 

Do you ever need to clean your extract ducts? Not even sure how I'd go about that...

 

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A recirculation hood to trap grease is a good idea. While the venting hob options are dearer, you do extract at point of source so very effective. The MVHR deals pretty well with odours so this I wouldnt worry about.

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I asked same question  of blauberg agent in uk   when talking about a centralized mvhr system  for new build 

his suggestion was to accept small loss  when in use and have it  separate direct extraction to outside with a flap type exit .

better than blocking up the mvhr filters and coating ducts internally over time with gunk 

just what I have been told 

you make your own mind up 

I know what I will do when i get that far 

 

Edited by scottishjohn

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Thanks Scottishjohn - I share your worry about keeping the MVHR clean.  Hopefully a recirculating system would do the trick without opening another route to outside.  I am past the point of putting any more holes in the walls!  

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FWIW, we have no problem at all with the MVHR or ducting getting dirty.  I cleaned/changed our MVHR filters last week, and as usual the fresh air intake filter was very dirty, but the house extract filter just had a very light coating of dust, so I just cleaned it with a vacuum cleaner and put it back.

 

I fitted an OSB panel and additional wiring behind the ceiling plasterboard above our hob, so it's pretty easy to retrofit a cooker hood, but we've found that we don't need a cooker hood in practice, as the kitchen MVHR extract terminal seems to do a very good job of drawing cooking smells etc away from the rest of the house.  One thing I did that probably helps this is fit an additional fresh air supply terminal in the ceiling outside and above the kitchen door.  This ensure than fresh air is supplied as a sort of "air curtain" outside the kitchen, which seems to stop any cooking smells from escaping.

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you don't do much stirfry though Jeremy.

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3 minutes ago, dpmiller said:

you don't do much stirfry though Jeremy.

 

 

No, that's true, in fact we rarely fry anything, which probably makes a significant difference. 

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@Besidethewye We have our MVHR kitchen extract around 2m from our hob and have fitted a recirculating extractor hood above the hob. Although we don't fry food we have planned ahead for when we no longer live here.

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I thought I had a plan and now I am not so sure!  

 

We have extracts about 2m from the hob one way and another in the utility about 3m the other but a possible route out of the kitchen and into the corridor/upstairs drawn by the extract in the toilet.....we don't fry a great deal though the better half does note that my repertoire in the kitchen is dominated by stir fries of various and unrepeatable mixtures.  

 

My aversion to a) having to make modifications later and b) finding gunk in the extract pipework which I can't see how we would ever clean out makes me think putting a recirc hood in now would be easier and my wish not to keep burning money unnecessarily suggests put the mounting in and move on....

 

I'll check with the boss for the definitive answer.  As they keep saying by the time I get onto my third house I might have it all down to a T

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23 minutes ago, Besidethewye said:

I thought I had a plan and now I am not so sure!  

 

We have extracts about 2m from the hob one way and another in the utility about 3m the other but a possible route out of the kitchen and into the corridor/upstairs drawn by the extract in the toilet.....we don't fry a great deal though the better half does note that my repertoire in the kitchen is dominated by stir fries of various and unrepeatable mixtures.  

 

My aversion to a) having to make modifications later and b) finding gunk in the extract pipework which I can't see how we would ever clean out makes me think putting a recirc hood in now would be easier and my wish not to keep burning money unnecessarily suggests put the mounting in and move on....

 

I'll check with the boss for the definitive answer.  As they keep saying by the time I get onto my third house I might have it all down to a T

I looked at price of one of those recirculting extracts that cone up out of an island 

 

over £3k-

I, won,t be doing that

it will be a direct to outside job with flap on outside grille 

 

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1 hour ago, scottishjohn said:

over £3k-

I, won,t be doing that

it will be a direct to outside job with flap on outside grille 

 

Seems crazzy expensive ! I will be renting my cottage out in the summer (what year I don’t know.....) and I know most of my guests like to have a holiday fry up when they are staying. I have wasted so much time going back and forth with what to do ! I don’t want gunk in my ducts and a mixture of dust and fat sounds like a disaster waiting to happen. I was planning on recirculating with an OVER SIZE hood to try and catch as much as possible but there is no way I would have a spare 3k...... maybe I need to pipe in a direct to outside extraction and use that until I can afford a recirculating hood.....  but 3k...... impossible. 

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7 minutes ago, Cpd said:

 

Seems crazzy expensive ! I will be renting my cottage out in the summer (what year I don’t know.....) and I know most of my guests like to have a holiday fry up when they are staying. I have wasted so much time going back and forth with what to do ! I don’t want gunk in my ducts and a mixture of dust and fat sounds like a disaster waiting to happen. I was planning on recirculating with an OVER SIZE hood to try and catch as much as possible but there is no way I would have a spare 3k...... maybe I need to pipe in a direct to outside extraction and use that until I can afford a recirculating hood.....  but 3k...... impossible. 

I,m sure there are cheaper ones that do not hide in island and only appear when you want to use it

-I stated that one as an example of how silly some the prices can be

a quick look 

https://www.tlc-direct.co.uk/Main_Index/Cooker_Hood_Index/Luxair_Hood_Index/Luxair_Recirculating/index.html

 £880-£1000

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If you want a quick and simple solution then fit a carbon foam filter block inside the extract vent - they are usually used for fish ponds but what they do is trap the grease and just wash it out every so often. Should be no more than £10. 

 

One question I would ask though of the people worried about cleaning the ducts on MVHR.... when was the last time you cleaned your extractor hood pipework ..???? I know a lot of people who change the filters but nothing else, and even with a filter due to the direct extract route these get very mucky yet we all seem to ignore it ..??

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I managed to modify the carbon filter on our old cooker hood by just removing the grilles either side of it and re-filling the core with activated carbon granules, intended for use with fish pond filters (they are cheap and easy to buy from places like eBay).  Worked a treat, and if you wanted to really save money then you can wash and bake the used granules to reactivate them.

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most peoples ducting will be  much shorter than any mvhr system though 

Edited by scottishjohn

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We have a recirculating extract over the hob that works really well. We also have an mvhr extract about a meter set back from the recirculating hood extract. The flow rate of the mvhr is many times lower than the extract hood, but over time removes any smells and the extract hood removes grease from the air.

We have a 30 year old rental apartment with constant extract above the cooker with no filters. The amount of grease this has collected over time and has stuck in the duct is disgusting and really shows the importance of something to trap the grease and not just rely on the mvhr to extract .

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1 minute ago, Alex C said:

We have a recirculating extract over the hob that works really well.

Do you have a  Make and cost of this please ? It’s something I will need in the future and don’t want to buy a lemon when the time comes. Also how big / wide is your hob  compared to the hood. 

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@JSHarris do I recall you added an ozone generator? If so, do you still use it?

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1 hour ago, Cpd said:

Do you have a  Make and cost of this please ? It’s something I will need in the future and don’t want to buy a lemon when the time comes. Also how big / wide is your hob  compared to the hood. 

It is an elica that was very expensive, but as we have an open plan kitchen living space I wanted one that looked good as well as being effective. https://elica.com/GB-en/hoods/meteorite-islandI'm sure it is possible to get ones that functions just as well for less money, although cheaper ones do tend to be more noisy. We have an 800 wide hob and wanted a 1200mm wide hood so that narrowed choices right down. Plenty of people use the ceiling recessed ones above island hobs, but with a high ceiling these are never going to be so effective. The standard for these seems to be the Westin oneshttps://www.westin.co.uk/our-hoods/ceiling-hoods/westin-stratus/.These were specced by all the high end kitchen companies I visited.

Edited by Alex C

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2 hours ago, richi said:

@JSHarris do I recall you added an ozone generator? If so, do you still use it?

 

I have a portable ozone generator that I used to use a bit at the old house to get rid of lingering cooking smells.  It works very well, just plug it in, close the door and come back half an hour later and there's no trace of any smells (kills all the bugs in a room too...).

 

I've not felt the need to use it in the new house, mainly as the MVHR is pretty effective at getting rid of any lingering cooking smells.  We do still have a small ozone generator that sits inside the fridge, and activates periodically to remove smells.  Seems to work well, especially if there are any pongy cheeses in the fridge.

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We use a small ozone generator to neutralise cooking odours. It certainly helps, especially if running whilst creating the odours. This is in addition to a recirc hood, and MVHR on boost. If more is required (e.g. when griddling steak) we'll open windows on opposite sides of the house and use the pressure differential to do quick air change.

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