Cooker Hood Extractor (a paste)

[Fallingditch]

 

Posted 25 March 2016 - 03:58 AM

Hi folks,

I know it's frowned upon in an airtight house with MVHR but myself and my wife are very keen for an externally ducted cooker hood for our new build.

We both like to cook and currently have a recirculating hood and tbh its hardly worth turning it on, so end up opening the kitchen window.

So, this evening I have been looking into hoods/ducting.

The plan is to have our induction hob on an island so have been looking at down draught extractor hoods like these -

http://www.besthoods...raft-extractor/

I know they are pretty expensive but our open plan kitchen, dining, living area will have a vaulted ceiling so can’t really have one of the overhead hoods.

Another positive I can see would be that I would assume these would have better airtightness than a conventional hood when not in operation....does anyone have any experience of this?

Another thing I stumbled upon that may help with air tightness was this draught excluder grill -

https://www.naber.de...rkasten-s04014/

Has anyone installed one of these?

Also, with regards to ducting from hood to external wall this may prove tricky with the hood/cooker being on the island.

My only thoughts are to run the ducting down from the island, under the slab to a kitchen cupboard unit (located beside an outside wall) and then up to a reasonable height before going through the external wall.

This method would involve at least three 90 bends and roughly 3m distance before cooking smells would be extracted outside.

Does it sound unrealistic for me to expect a good form of effectiveness from this?

#2dampindevon

Posted 25 March 2016 - 09:47 AM

Have a look at berbel.de they have a wall box which could be ideal, no idea of price and they also do some rather lovely extractors just don't let the wife see them 

#3ryder72

Posted 25 March 2016 - 10:10 AM

I am in the same position and we will be installing a powerful ceiling recessed extractor with external motors. Cooking it too important to us to compromise.

I am really not convinced downdrafts are the best extraction solution. For starters, there is the physics of rising heat. Then there is the complexity of ducting - it invariably involves multiple 90-degree bends, each one reducing extraction efficiency and increasing noise level. Unless one can use circular 150mm dia ducting (highly unlikely given it has to run under a slab) space restrictions demand use of flat channel ducting. Use 6 inch equivalent ducts (I would highly recommend Naber products) and an external motor will be the way to go but all of this puts up the price.

I would also steer clear of Best products. From my experience, I would only trust Gutmann or Bora hoods for downdrafts. Rest of the products on the market are commercial products designed to jump onto a design bandwagon.

Is a suspended hood not an option? These can be easily attached to vaulted ceilings and many manufacturers offer chimey sections that you can get cut to the right angle by a metal fabricator. 

#4ryder72

Posted 25 March 2016 - 10:11 AM

Berbel is a very good product but their after sales presence is the UK is very sketchy. 

#5rossek9

Posted 25 March 2016 - 12:53 PM

dampindevon, on 25 March 2016 - 09:47 AM, said:

Have a look at berbel.de they have a wall box which could be ideal,no idea of price and they also do some rather lovely extractors just don't let the wife see them

Yeah I came across the berbel wall box as well but the £420 price tag is something that put me off. It's seems excessive to spend upwards of £1k on a extractor hood and another £400 on a mechanical vent tbh. 

#6rossek9

Posted 25 March 2016 - 01:11 PM

ryder72, on 25 March 2016 - 10:10 AM, said:

I am in the same position and we will be installing a powerful ceiling recessed extractor with external motors. Cooking it too important to us to compromise.

I am really not convinced downdrafts are the best extraction solution. For starters, there is the physics of rising heat. Then there is the complexity of ducting - it invariably involves multiple 90 degree bends, each one reducing extraction efficiency and increasing noise level. Unless one can use circular 150mm dia ducting(highly unlikely given it has to run under a slab) space restrictions demand use of flat channel ducting. Use 6 inch equivalent ducts (I would highly recommend Naber products) and an external motor will be the way to go but all of this puts up the price.

I would also steer clear of Best products. From my experience, I would only trust Gutmann or Bora hoods for downdrafts. Rest of the products on the market are commercial products designed to jump onto a design bandwagon.

Is a suspended hood not an option? These can be easily attached to vaulted ceilings and many manufacturers offer chimey sections that you can get cut to the right angle by a metal fabricator.

Glad I'm not the only one not willing to budge on external cooker extraction. It's something my wife and I feel pretty strongly about given previous experiences.

The problem we have it that our vaulted ceiling will have a ridge height of 4.5m so the extractor hood would need to have a chimney length of upwards of 2m. Given this will be on the island I can't see this being stable with no wall fixing points available?

We did have thoughts to make up a floating overhead hood fixed to either outside wall so the duct could run through this. The length of this from outside wall to outside wall would be 4.6m though and if this envolves additional steels due to weight this may increase costs more than a down draught hood. Do you think this option would be better further investigated?

The other worry we have is a floating hood connected to both outside walls may impact a bit on the open plan nature of the space.

Thanks for the advise on hoods to look for. It's really not something I have done a huge amount of work looking into yet but if ducting needs to be run under the slab then I need to make decisions on this at the outset. 

#7rossek9

Posted 25 March 2016 - 01:13 PM

ryder72, on 25 March 2016 - 10:11 AM, said:

Berbel is a very good product but their after sales presence is the UK is very sketchy.

The price difference between the barbel and one I've linked above is around £300 as well, which is a consideration. 

#8JmS

Posted 25 March 2016 - 01:18 PM

Ryder72, what products are you using external motors wise. By external do you mean external to the house?

I am still working out how to find a closer/damper for our kitchen

Thanks
James 

#9jsharris

Posted 25 March 2016 - 01:23 PM

It is worth bearing in mind that a house with MVHR is VERY different to one without. I've experienced the near-useless performance of a recirculating cooker hood, and ended up fitting the external vent kit. However, I friend has a recirculating hood fitted in a well-sealed house with MVHR and she finds that it works extremely well indeed. I think the main difference is that the hood removes the fat and oil vapours and the MVHR on boost is very effective at removing the stale air from the kitchen, so the net result is that the performance of the cooker hood is far better than might be expected.

Fitting an external vent will make a very big difference to the heat loss. When working it pumps out warm air that then needs to come in from somewhere, and if you have MVHR it will become massively out of balance and so will lose a great deal of efficiency (you'll find that all the fresh air feed ducts start feeding cooler air into every room). The other issue is that it is near-impossible to get an effective seal on an extract duct, so not only will it be a cold bridge when not in use (and hence a condensation focus) but it will also be a constant cold air leak into the house, or warm air leak out of the house, and in any sort of a breeze may well unbalance the MVHR.

If it were me, then I'd look at designing the house to be "fitted for, but not fitted with" a cooker extract duct. In other words I'd fit the ducting (but not put the hole through the wall yet) and fit the wiring and necessary mechanical supports, but fit a recirculating hood that can be converted to an extract hood just by making a hole in the wall. Live with it for a while with it working as a recirculate only hood, and if you find that it doesn't work well enough then look at externally ducting it.

Based on the performance of my friends recirculating hood in a house with MVHR I'm convinced one isn't needed at all, especially when you can boost the MVHR to get cooker hood type extract rates from the kitchen anyway. 

Edited by jsharris, 25 March 2016 - 01:24 PM.

#10ryder72

Posted 25 March 2016 - 11:07 PM

I will be using Gutmann. Experience of working with at least 10 brands of cooker hood manufacturers I have reached the conclusion that no one makes his as well as gutmann in general.

The hood will have an external motor able to operate at 1200m3 per hour and should be able to handle a griddle, wok and a 6 zone hob without a problem.

Jeremy I am aware of the potential problems of mvhr and I have seen mvhr systems work with houses and serious cooks and the two instances I have seen had evidence of stale air and lingering cooking smells. We are going to link our cooker remote to a high level slot window that has been specified as electrically opening so the operation of the hood will trigger the hood opening as well to allow another source of air into the house and aid the air flow. Ceiling recessed hoods are unfortunately not switchable products that can go from recirc to vented and with the external motor it will be a decision made quite early iin the process. 

#11ryder72

Posted 25 March 2016 - 11:09 PM

Rossek9 I don't know what to suggest. I can recommend a bespoke extraction manufacturer who are good but not cheap. PM me if you like 

#12rossek9

Posted 26 March 2016 - 01:43 AM

Thanks for the posts jeremy and ryder.

I think this needs further thought from myself.

I do love to cook a curry on a friday night and the smell of fried onions lingers for days in our current home, even with the back door open, window open and recirc hood on!!!

This has been what has promted our want to go with an externally vented hood.

I have looked at the gutmann hoods ryder but cant see any prices.................if you need to ask, you cant afford one, comes to mind.

Still like the idea of the floating hood, which may not be too much for a joiner to fabricate up and might add a nice focal point (or so the wife says).

Also, I thought today this may also be ideal for running the breakfast bar lighting rather than having pendents coming down from the vaulted ceiling. 

#13ryder72

Posted 26 March 2016 - 07:56 AM

rossek9 - Here is an idea - get a timber frame clad in or veneered oak/walnut made by a carpenter and install the hood within it. Suspend it down from the ceiling on steel wires. Run a commercial grade 6-8 inch insulated flexi duct (the type that has a metallic finish on it to) from the top of this boxing to your ceiling and vent out through an appropriate outlet. Ensure that this vent isnt going to be a restriction to your desired flow rate.

If the industrial look works for you, then this solution will work.

Gutmann is supplied only through specialist retailers due to the professional grade of their product so you are unlikely to find it online. 

#14bitpipe

Posted 26 March 2016 - 10:49 AM

We've specced a Siemens recirculating hood over the hob in our kitchen and I've installed a dedicated MVHR extract vent about 1m in front of it.

Our MVHR unit has a 'cooker hood' mode that's activated via a dedicated terminal so it will go into a pre-programmed boost mode automatically while the hood is running.

This vent currently has a single duct run, there is another extract in the kitchen that has two duct runs, so there will be plenty of extract capacity in that area.

I'd really advise reading Jeremy's post carefully - if you're spending the time, effort and money to ensure that the house is airtight then you're massively compromising this by effectively making a big hole in your wall that completely bypasses your heat recovery system.

Personally, I'd not frame this decision as a simple style choice that's 'frowned upon' by outsiders (like installing a 70's avocado bathroom suite  ) but a pretty significant building design decision that will fundamentally impact the performance of your house and needs to be considered carefully and if necessary compensated for in your overall heating and ventilation design. 

Edited by bitpipe, 26 March 2016 - 10:50 AM.

 

#15Nickfromwales

Posted 26 March 2016 - 02:58 PM

This is the reason I've started to look at incorporating an electro-mechanical damper / shutter in my house extraction setup. 
No back draught and no convection heat loss when the fans off. About as good as a middle of the road solution as you'll find imo, and even more so for a PH where extraction is required in excess of the mvhr rates. 
@bitpipe. Do you mean your mvhr only boosts extract at the kitchen terminal? Most boost the whole house iirc. 
Regards, Nick 

#16PeterW

Posted 26 March 2016 - 03:02 PM

I'm amazed no-one has come up with an extractor hood that has heat recovery in it ..! One that used carbon filters and also some thing like the copper wire exchange system that the Viking House vent does so you get the best of both worlds. 

And as nick says, a decent flap system to stop the drafts when it's off... 

#17ryder72

Posted 26 March 2016 - 04:23 PM

The Naber or Berbel pressure actuated vents work well and prevent a back draught.

I think the problem with building a heat exchanger into a vented hood is that heat exchanger plates will reduce flow rates and as Jeremy said, imbalance the MVHR.

For this reason I came up with what was a 'simpler' mechanism of automatically opening a window with the hood. I know its not as scientific as it could be, but for us the house would be a 'fail' if any cooking odours lingered and its a risk we arent prepared to take.

German companies working on this are working on plasma ionisation filters where the grease filtered air gets passed through some sort of chamber which breaks down odour causing molecules and pumping air back into the room. It is an expensive product. 

#18stones

Posted 26 March 2016 - 04:27 PM

Jeremy has previously commented on the impact his home made ozone generator had in clearing cooking smells. Could this be a possible solution (used in moderation of course)? 

#19jsharris

Posted 26 March 2016 - 04:49 PM

stones, on 26 March 2016 - 04:27 PM, said:

Jeremy has previously commented on the impact his home made ozone generator had in clearing cooking smells. Could this be a possible solution (used in moderation of course)?

That's a good point. I didn't build the unit to do this, but there is no doubt that a small amount of ozone does get rid of smells very quickly and effectively. Simple ozone generators for use for short periods are pretty cheap; I'm using the parts used in these as the basis for the ozone system that oxidises the ferrous iron and manganese in our borehole water. The only problem with the simple ceramic plate ozone generators is that the corona plates get very hot, and when they heat up the ozone generation drops and their life is shortened. The better designs fit heat sinks to the plates, which helps, but for occasional use (for 20 minutes or so at a time) the simple units with just a fan cooling the plate and distributing ozone are very effective.

We have a small, battery operated, ozone generator in our fridge. It only comes on in short bursts, and the battery lasts a long time, but it's very effective at controlling smells. Before we had it the fridge would often smell quite strongly if there had been some particularly smelly cheese or seafood in there, now it never has the slightest smell of anything. Not altogether a good thing, as the effectiveness of the ozone masks the smell of things like milk going off. 

Edited by jsharris, 26 March 2016 - 04:50 PM.

#20stones

Posted 26 March 2016 - 04:57 PM

Just had a quick look and as you say, they do seem cheap.. Generating capacity seems to dictate price. This one for example 

http://www.ebay.co.u...YMAAOSwr7ZW6PpY

indicates 600mg an hour. I've no idea if that's a meaningful amount or not. I would only want to be running such a device for short periods to clear any lingering odours. Would something like this one do the job or would I need something with a bit more capacity? 

 

#21jsharris

Posted 26 March 2016 - 05:05 PM

They all tend to massively over-state their output, as they test them on dry oxygen as the feed gas, so when run on air at normal humidity levels they tend to deliver a bit less than 1/5th of their rated output. I can say that my 7g/hour rated unit is far too powerful to use in a room. After a minute or so your eyes are stinging and it's painful to breathe the air, there's that much ozone in it. That makes me think that a much smaller unit like the one linked to may well be adequate, depending on the size of the room.

I did play with the idea of adding ozone to the MVHR fresh air feed, as a way of helping to remove lingering smells, and may well look at doing it when I've got a bit of spare time. There is a great deal of misinformation on the web, and almost a cult of "ozone therapy", but there is no doubting the powerful oxidising and deodorising effect that it has. 

#22PeterW

Posted 26 March 2016 - 05:20 PM

I've ordered an ozone generator for my rainwater tank to both kill off some of the nasties and also to do a first stage on the cleaning before it heads through the filters. It's a cheap and cheerful one and all it has is an aquarium pump and then the ozone tube. I'm going to put a silica gel packed drying tube in the flow as they work better apparently on dry air. Also considered if two tubes in series was better than one. 

Adding one into a cooker hood would be pretty simple I expect and the tube would be in a pretty decent airflow to cool it when it's on - only noisy bit is the air pump. 

#23jsharris

Posted 26 March 2016 - 06:38 PM

They definitely work better with dry air. My set up for injecting ozone is a small air pump that blows air through a 4" water filter housing, with a refillable inner cartridge that is supposed to be used to hold activated charcoal. I filled it with colour indicating silica gel beads and bought enough beads to fill two cartridges, so I could be regenerating one whilst the other is in use. Dry air is then fed to a home made ozone generator, using a two ceramic plate unit that I've modified, so the plates are bonded to a big alloy heatsink to keep them cool. There's a sealed chamber over the plates, so the pressure is maintained. The air+ ozone is then fed down a long length of 8mm HDPE pipe to a venturi mixer at the well head, that creates enough suction to draw in just about the right amount of air and ozone every time the pump turns on (the ozone generator only runs when the well pump runs).

The oxidation takes place in the whole pipe run back to the main GRP aeration tank, which has an air/ozone bubble maintained at the top, by virtue of a dip tube that goes part way into the tank and has a float type automatic air bleed on top. This vents off excess air/ozone and water is drawn from the bottom of this tank, along with particles of ferric iron resulting from the oxidation reaction. The particles get filtered out by the backwashing sand and oxidising media filter, that also oxidises any ferrous iron or hydrogen sulphide that didn't get treated initially.

In practice we now get very good quality water, with no taste of smell, from a well that delivers pretty smelly water with a lot of iron in it. The key seems to be just oxidising out the stuff you don't want in the water, and the ozone definitely helps with that, by significantly increasing the ORP of the water right at the point where it is pumped up. 

#24rossek9

Posted 26 March 2016 - 07:21 PM

ryder72, on 26 March 2016 - 04:23 PM, said:

The Naber or Berbel pressure actuated vents work well and prevent a back draught.

I think the problem with building a heat exchanger into a vented hood is that heat exchanger plates will reduce flow rates and as Jeremy said, imbalance the MVHR.

For this reason I came up with what was a 'simpler' mechanism of automatically opening a window with the hood. I know its not as scientific as it could be, but for us the house would be a 'fail' if any cooking odours lingered and its a risk we arent prepared to take.

German companies working on this are working on plasma ionisation filters where the grease filtered air gets passed through some sort of chamber which breaks down odour causing molecules and pumping air back into the room. It is an expensive product.

The berbel states on its website that the insulation value is 0.95 W/m2K of the wall box. I can’t seem to find anything on the Naber but will have a further look tonight.

I fully understand everyone’s comments regarding extraction and mvhr being unbalanced so it’s something I really need to think about in more detail.

We are a long way off deciding on hoods tbh (amended planning for our house design was submitted last week), but it's something I don’t what to overlook and regret further down the line.

I think we have come to the decision that if anything we will look to design an overhead hood incorporated into some sort of hovering beam/joist arrangement. I’m not sure if in explaining my vision here very well but I have an idea of how this work look in my head.

Maybe by the time we come to second fix some hoods may be designed that connect into the mvhr but don’t clog all the ducts with grease/fats/oils.......fingers crossed 

Edited by rossek9, 26 March 2016 - 07:23 PM.

#25gravelld

Posted 26 March 2016 - 08:22 PM

ryder72, on 26 March 2016 - 04:23 PM, said:

The Naber or Berbel pressure actuated vents work well and prevent a back draught.

Back draught is not the only problem.

Interested to hear about proper positively closing, airtight closers. 

#26RoundTuit

Posted 26 March 2016 - 09:53 PM

I'm also tending towards external extraction even with mvhr. I'm hoping that the relatively short, sharp period of extraction during cooking won't upset things too much, but the price of decent in-ceiling kit is a bit steep. Has anyone tried to diy it? A good in-line fan (hard wired to a multi-speed switch), as many led lights, as you want, and some sort of grease extractor on the intake (I guess that's the tricky bit...)? 

#27ryder72

Posted 26 March 2016 - 10:01 PM

Naber vents are pressure actuated at 150Pa on the 150mm dia system. It's a mechanical system. 

#28bitpipe

Posted 26 March 2016 - 10:22 PM

Nickfromwales, on 26 March 2016 - 02:58 PM, said:

@bitpipe. Do you mean your mvhr only boosts extract at the kitchen terminal? Most boost the whole house iirc.
Regards, Nick

No, not that smart as all extracts go to the same distribution box and the extract port of the unit - i think it's to do with the duration of the boost cycle, will check the installation instructions  

Edited by bitpipe, 26 March 2016 - 10:22 PM.

#29jayroc2k

Posted 27 March 2016 - 11:58 AM

Just to weigh in on external extraction with MVHR (I live in one).

All depends on your lifestyle and cooking habits.

If you are home during the day, cook non smelly and non fry foods (mash, rice, occasional stews, potatoes and veg), you will be fine depending on the MVHR.

For this scenario 
- arrive home in the evening and cooks a lot
- cook exotic foods (Indian, carribean, Asian)
- open plan kitchen

In the above scenarios, waiting for hours for the MVHR to clear the air will mean a smelly living space until it's bed time (not pleasant). 

I will strongly suggest you externally extract. An imbalanced MVHR or inefficiencies are a small price to pay for having the open all windows to compensate or sit with the lingering food smells every evening. 

#30ryder72

Posted 27 March 2016 - 04:09 PM

I would say we definitely sit in the latter category. A large open plan area of approx 80m2 leading to a double height vaulted area. Cook a wide variety of food every evening and weekends and entertain regularly including a lot of grilled meats.

Based on this, I am not prepared to take the chance that smells dont clear out immediately and effectively.

To counter MVHR imbalance to the greatest extent possible, I have opted for a self opening window triggered by the hood operation which to an extent should make no difference to the MVHR operation. Admittedly this may cause a lot of heat loss when the hood operates and there may be a thermal bridge along the duct (I plan to put in a 150mm round section duct lagged externally and connected to a pressure actuated vent) but this is a price I am willing to pay. The heating system is an oil boiler coupled to a thermal store, so I dont think we will have any problems countering the heat loss. 

#31declan52

Posted 27 March 2016 - 04:39 PM

I have my extract straight out via a spring loaded system on the duct. My kitchen, dining room is approx 60sqm.Not the best option but it works for me. Its on the list of things to upgrade so when a better option becomes available for not silly money i will change it. I have a mhrv vent approx 1m from my hob and it will eventually get rid of the steam but by the time it does the smell will have started to annoy me. It is vented via a 150mm duct wrapped in rockwool the whole way to a vent tile on a sheltered part of my roof. It was simply a trade of for me between getting rid of the smells, I love cooking curries etc from scratch, and some heat loss.
Had a recirculating hood in my last kitchen and it was dire. Windows always had to be opened even the back door when it got really bad. 

Edited by declan52, 27 March 2016 - 04:39 PM.

• rossek9 likes this

 

#32rossek9

Posted 27 March 2016 - 05:45 PM

Ryder and Declan,

We are in the same boat as yourselfs. Open plan area is 60m2 with vaulted ceiling and to add to that curries/asian/stir fries are the norm in our house.

In fact, our wok just lives on our 5 ring hob as we use it every night.

declan52, on 27 March 2016 - 04:39 PM, said:

I love cooking curries etc from scratch, and some heat loss.
Had a recirculating hood in my last kitchen and it was dire. Windows always had to be opened even the back door when it got really bad.

Declan, this could have been written by me!!! We have to do the exact same thing atm

If we dont install an external extract hood with something like the Naber mechanical vent and I end up opening our big sliders everytime I cook, I dont see how this makes any difference to the mvhr balance anyway.

Would same me the cost of a hood and mechanical vent though. 

#33jsharris

Posted 27 March 2016 - 08:17 PM

Opening a door or window has little effect on MVHR balance, unless there's a gale blowing.

Turning a big extract fan on has a massive effect, as the suction from the extract will probably be many times the flow rate from the MVHR. The effect will be to draw many times more air through the fresh air feed side of the MVHR, whilst reducing the flow through the extract side, so the heat exchanger simply won't be doing much and loads of air that's hardly been warmed at all will flow into every room with a fresh air vent, cooling all those rooms down. If the extractor is of industrial size, you may well find that the living rooms, bedrooms etc all get a bit noisy from the big increase in fresh air being drawn in through ducts and terminals that will have been sized for a much lower flow rate.

In order to reduce the impact of this, then it would be very sensible to open a window or door in the kitchen, and close the internal doors from rooms fed with fresh air, to reduce the whole house pressure drop that the extractor will create otherwise and hopefully reduce the negative impact of the MVHR imbalance. 

#34rossek9

Posted 27 March 2016 - 08:26 PM

jsharris, on 27 March 2016 - 08:17 PM, said:

Opening a door or window has little effect on MVHR balance, unless there's a gale blowing.

Turning a big extract fan on has a massive effect, as the suction from the extract will probably be many times the flow rate from the MVHR. The effect will be to draw many times more air through the fresh air feed side of the MVHR, whilst reducing the flow through the extract side, so the heat exchanger simply won't be doing much and loads of air that's hardly been warmed at all will flow into every room with a fresh air vent, cooling all those rooms down. If the extractor is of industrial size, you may well find that the living rooms, bedrooms etc all get a bit noisy from the big increase in fresh air being drawn in through ducts and terminals that will have been sized for a much lower flow rate.

In order to reduce the impact of this, then it would be very sensible to open a window or door in the kitchen, and close the internal doors from rooms fed with fresh air, to reduce the whole house pressure drop that the extractor will create otherwise and hopefully reduce the negative impact of the MVHR imbalance.

Thanks for keeping me right jeremy, still trying to learn all these things........and fast!! 

Edited by rossek9, 27 March 2016 - 08:30 PM.

#35jsharris

Posted 27 March 2016 - 09:00 PM

If you want to see the effect for real, try and blag a visit to a house that's being pressure tested, with a blower door/window. The blower will be a lot less powerful than a decent kitchen extractor, you can barely feel the flow through it at the fan.

However, if you go around the house trying to find leak points you will often hear them howling, even at the very low pressure differential used for testing, just 50 Pa. I have a home made blower that I used to help find leaks and better seal our old house. It uses a car electric radiator fan with a variable speed control. Even on our relatively leaky old house, that fan, running quite slowly, will make all the keyholes howl. If the house was to the sort of airtightness level that a new house would be then the noise from even tiny leaks will be surprisingly loud. 

#36bitpipe

Posted 28 March 2016 - 10:28 AM

This is a great thread and giving me food for thought - our kitchen / diner / living is open plan (but has a modest 2.4m ceiling height throughout. House layout is roughly square.

Living, dining & study (which has a door) all have fresh supply in each corner and the kitchen has two extracts - one double ducted in the corner and one single ducted between the cooker hood and oven on the opposite wall.

I'm going to see if I can add an extra exhaust duct run to the hob vent just to maximise its extract capacity, I have a spare extract port on the distribution box - failing that, I may just move one duct from the corner extract to the hob extract unless that would cause an issue?