Do I really need an extractor in kitchen?

[jamiehamy]

Hi all, 

 

So we are hopefully about to finalise the kitchen, after spending 5 hours with the chap so far. 

 

We 'require' a downdraft extractor on our island, and they are working out around £1300, but also, as we need a 900 wide one for the hob, it's messing the island layout slightly (even a 660mm one is a pest). 

 

I understand the chat around recirculation, but I'm wondering if really, we need it, or it's going to be a fancy ormanent that goes up and down at the push of a button but is not justifying the very high cost. 

 

We have MHRV in place to take away the warm and damp air, and eventually any smells - is a downdraft going to be something that is needed, or just nice to have? In terms of capturing grease - are downdrafts really effective at this and without it, is there going to be a tangible difference we may notice?

 

Happy to hear all thoughts - D-Day is Wednesday for final design!

 

Cheers, Jamie 

 

[Construction Channel]

is the BCO demanding this or just the kitchen supplier

 

[Trw144]

I have to say I rarely turn our kitchen extractor on (ricurculation type as I have mvhr). I once felt the need to open the door but that was my cooking more than an issue with anything else.

 

Edited February 18, 2017 by Trw144

[jamiehamy]

6 hours ago, Construction Channel said:

is the BCO demanding this or just the kitchen supplier

 

No-one! I just assumed it was needed.. 

[Barney12]

I've been doing a lot of digging on this issue as the costs are eye watering. 

 

The general consensus is "if its recirculating, don't bother". But you get the opposite view from someone trying to sell you one!

The answer is partly driven by "how much" and "what" you cook. The reality I've come to realise is our hob is used very infrequently as veg is generally steamed and we rarely fry. In fact our cooking could be described as "basic". 

 

My wife though has taken some convincing on the issue! 

[Ferdinand]

Is this like ufh?

 

Put the hidden ducting in but leave it sealed and a future owner or you if you turn to be Escoffier can fit the hood.

 

F

[jamiehamy]

6 minutes ago, Ferdinand said:

Is this like ufh?

 

Put the hidden ducting in but leave it sealed and a future owner or you if you turn to be Escoffier can fit the hood.

 

F

We can put in the cable and there will be room for ducting possibly - but that would require a retrospective cut of the Quartz surface... 

[AliG]

Hi Jamie,

 

I thought you had to have an extractor, but this is what the regs say -

 

either:

1. mechanical extraction capable of at least 30 litres/sec (intermittent) above a hob [2]; or

2. mechanical extraction capable of at least 60 litres/sec (intermittent) if elsewhere [3]

 

So if your MVHR has that extract rate then you don't need an extractor. The MVHR people may worry though that without an extractor the MVHR will get grease in it. Of course they can't guarantee that you don't turn on the extractor anyway. Also as I understand it, it is not ideal to have a ducted extractor and MVHR as it unbalances the MVHR. It also is bad for airtightness.

 

I have the hob in the island, but am putting the extractor in a box in the ceiling that matches the shape of the island(it is recirculating and doesn't count anyway towards the extraction regs). Kitchen designers were pretty against the downdraught extractor. They said they are expensive and waste a lot of space in the island.

 

I wonder though with the hob being in the island that air won't get trapped like it would against a wall and the extractor isn't necessary. Maybe someone who already has one can comment.

 

 

Edited February 18, 2017 by AliG

[Jeremy Harris]

13 minutes ago, AliG said:

Hi Jamie,

 

I thought you had to have an extractor, but this is what the regs say -

 

either:

1. mechanical extraction capable of at least 30 litres/sec (intermittent) above a hob [2]; or

2. mechanical extraction capable of at least 60 litres/sec (intermittent) if elsewhere [3]

So if your MVHR has that extract rate then you don't need an extractor. The MVHR people may worry though that without an extractor the MVHR will get grease in it. Of course they can't guarantee that you don't turn on the extractor anyway.

 

I have the hob in the island, but am putting the extractor in a box in the ceiling that matches the shape of the island. Kitchen designers were pretty against the downdraught extractor. They said they are expensive and waste a lot of space in the island.

 

I wonder though with the hob being in the island that air won't get trapped like it would against a wall and the extractor isn't necessary. Maybe someone who already has one can comment.

 

 

 

 

Not sure that's right, is it?  The regs are different for whole house ventilation, I believe, as the very last thing you want with MVHR is an extractor that will massively unbalance the system and cause cold air to flow into all the fresh air fed rooms every time it's running.  Column one in Table 5.1a in Part F does not apply to continuous ventilation, for that you use the figures in column 2, so there is no part F requirement for the 30/l/s / 60l/s hob extract if you have MVHR.

 

 

 

 

Edited February 18, 2017 by JSHarris

[AliG]

You're right @JSHarris, I was just editing my answer as I didn't realise @jamiehamy was proposing a ducted extractor in a house with MVHR. If you have one it should be recirculating.

 

Reading the Scottish regs I think what I posted stands, that the MVHR should be able to provide 60l/sec of extraction of air from the kitchen.

 

Ah. I just looked at Part F that you refer to and this has 13l/sec for continuos extract. This isn't mentioned in the Scottish regs.

 

Eventually I found that the kitchen regulation for continuous mechanical extract is 0.5 ACPH and 25-50% boost.

 

 

Edited February 18, 2017 by AliG

[Jeremy Harris]

60 l/s is an massive flow rate for an MVHR terminal, and it would probably mean over-sizing the MVHR just to achieve that rate in the kitchen on boost.  I'm not familiar with the Scottish Building Regs, but if that's what they say then they are a bit odd, as it means that the MVHR total efficiency will be poor 99% of the time, because the thing will have to be sized to meet a kitchen extract rate that's more 4 times that needed for full boost under the UK regs.

[AliG]

I thought so too @JSHarris eventually I found that the MVHR standards are in a different section in Scotland and weren't coming up when I was searching the standards.

 

The normal standards are in 3.14.3 of the Scottish Regs, the MVHR standards are in 3.14.11, I had to download the entire building stands handbook to find 3.14.11. If you search for sottish building standards ventilation that clause is not included 

 

Kitchen	6 litres/sec with 13 litres/sec boost
Utility room	4 litres/sec with 8 litres/sec boost
Bathroom	4 litres/sec with 8 litres/sec boost
Toilet	3 litres/sec with 6 litres/sec boost

 

Just to be odd the Scottish government also produce a guidance paper that says this -

 

http://www.gov.scot/Resource/0040/00409104.pdf

NFILTRATION RATE: 5 — 10m3/h/m2

Example Ventilation Solution 4: Continuously Operating Balanced Supply and Extract (with or without Heat Recovery)

Apartment	Kitchen	Bathroom / Shower	Toilet	Utility Room
1/30th floor [1] area			1/30th floor [1] area
12000 mm2	10000 mm2	10000 mm2	10000 mm2	10000 mm2
0.5 ACPH minimum	0.5 ACPH minimum and 25 -50% boost	0.5 ACPH minimum and 25 -50% boost	0.5 ACPH minimum	0.5 ACPH minimum

Edited February 18, 2017 by AliG

[ProDave]

So the Scottish regs require a continuous ventlation rate of 0.5 ACPH

 

My kitchen / dining room is 4.8 metres by 6.8 metres and 2.4 metres tall so a volume of 78336 litres.  So we need to change half of that per hour = 39168 litres per hour which works out at 10.88 litres per second for the whole kitchen which will be via at least 2 mvhr extract vents. So not much ventilation needed only 5.4 l/s per vent terminal.

 

Plus the ability to boost at 50% (I am sure our boost will be more like 100%)

 

[JanetE]

I clean our extractor regularly in the current house and I have to say it really picks up a lot of grease. I think you need one to do just this as otherwise the fat in the air will settle on near surfaces and I suspect your MVHR extractor will also pick up a lot and be pretty difficult to clean.

[joe90]

In my kitchen I plan to use a re circulating hood ( not vented to outside but has carbon and grease filters) and an MVHR terminal a 

Little further away from the cooker.

[ryder72]

Apart from what regs say about extractors, I would say they are essential for 2 reasons-

 

Grease removal - Anyone who wears eyeglasses and has tried to fry without good extraction will testify to this. Grease gets everywhere, carried by air currents generated by cooking heat and this will settle on worktops, floor, kitchen units and walls leading to dirt build up, musty smells, discolouration.

 

Odour/moisture removal - This is somewhat aided in houses with MVHR systems but nothing beats removal of odours and moisture at source.

 

I would recommend an adequately specified extractor with a good quality grease filter and possibly activated carbon filters too (if recirculating). I will be installing a ducted extractor in my house even with MVHR.

[Declan52]

Why does it have to a built into the hob type extractor can you not have a normal one above the hob that either vents out or recirculates???

[Bitpipe]

We have a large Siemens extractor over the induction hob, it's a bit of a beast and the centre piece of the kitchen but looks great and seems to work well. It has a recirculation unit and we have a MVHR extraction duct about 1m in front of it, plus another in the corner of the kitchen. 

 

It works pretty well on smell and grease removal, however it has its limitations and theres been a few times I've needed to open a window - normally because I've 'overcooked' something  

 

One note, extractors and the recirculation units are VAT exempt kitchen appliances for new builds as they're considered building fabric, not appliance. This may skew when you decide to buy it. We just got our kitchen supplier to zero rate it in the invoice. 

[Jeremy Harris]

The major problem with an outside extractor in a house with MVHR is that when it's on you will get cold air draughts coming in through every fresh air feed.  What happens is that you're sucking air out of the kitchen and fresh air has to come in somewhere, and the easy route in is via the MVHR fresh air inlets.  The MVHR will go massively out of balance and so the heat exchanger performance will degrade a great deal.  The result is that the incoming fresh air won't be heated to any significant degree and the incoming fresh air flow rate will increase to match the extractor flow rate.  The result, in cold weather, will be cool air coming out of the fresh air inlet terminals at a higher flow rate, just to compensate for the kitchen extract rate.

 

I posted somewhere else about how easy it can be to clean and refurbish the grease and activated carbon filters in a recirculating hood.  I do ours about every six months or so, depending on whether or not it looks like it needs a clean.  It's just a matter of sticking the stainless grease filter mesh in the dishwasher and refilling the carbon filter unit with fresh carbon granules (which can be bought in bulk pretty cheaply from fish pond equipment suppliers).  This works well, and keeps the everything clean around the hob in our current house.

Edited February 18, 2017 by JSHarris

[ryder72]

3 minutes ago, JSHarris said:

The major problem with an outside extractor in a house with MVHR is that when it's on you will get cold air draughts coming in through every fresh air feed.  What happens is that you're sucking air out of the kitchen and fresh air has to come in somewhere, and the easy route in is via the MVHR fresh air inlets.  The MVHR will go massively out of balance and so the heat exchanger performance will degrade a great deal.  The result is that the incoming fresh air won't be heated to any significant degree and the incoming fresh air flow rate will increase to match the extractor flow rate.  The result, in cold weather, will be cool air coming out of the fresh air inlet terminals at a higher flow rate, just to compensate for the kitchen extract rate.

 

I posted somewhere else about how easy it can be to clean and refurbish the grease and activated carbon filters in a recirculating hood.  I do ours about every six months or so, depending on whether or not it looks like it needs a clean.  It's just a matter of sticking the stainless grease filter mesh in the dishwasher and refilling the carbon filter unit with fresh carbon granules (which can be bought in bulk pretty cheaply from fish pond equipment suppliers).  This works well, and keeps the everything clean around the hob in our current house.

Completely take on board what you say. I am willing to go as far as to open a window when the hood is in use to compensate for the suction, but the risks involved with not having sufficient extraction for the amount of cooking that goes on in the house make me very uncomfortable with the idea of just recirculating. That said, I am investigation a soon to be launched Bora range very closely.

[Jeremy Harris]

My own view is that our MVHR is changing all the air in the house at least every 2.3 hours, 24/7, at trickle ventilation rate, that increases to all the air in the house being changed in less than an hour at boost rate.  Most of the extract air is from the kitchen, as that's the highest flowing extract duct, even at the trickle ventilation rate, and as our kitchen, utility and downstairs WC all draw fresh air in through the kitchen door, from fresh air feeds in other rooms, the chance of cooking smells escaping is pretty small.

 

The MVHR really is very effective at removing smells.  When we were painting and oiling the woodwork, there would be no trace of any "fresh paint smell" the next morning.  I'm pretty sure this is just down the MVHR being many more times as effective at properly ventilating the house than trickle vents, leaving a window open, or whatever, probably because it's not really affected much by outside conditions and is running all the time.

Edited February 18, 2017 by JSHarris
typo, "NVHR" when I meant "MVHR"...........

[jamiehamy]

Sorry,  would be recirculating - just means ducting to extract from under the island back into the kitchen. 

 

We can't have an overhead unit as 1 - there is a skylight just to the left and 2 -  the ceiling is at 5degrees, and 2.6meters high so not really an option.  Hmm mm! 

[Guest Alphonsox]

Have you considered the Bora type combined hob+extractor systems?

[ryder72]

On 18/02/2017 at 10:43, JSHarris said:

My own view is that our MVHR is changing all the air in the house at least every 2.3 hours, 24/7, at trickle ventilation rate, that increases to all the air in the house being changed in less than an hour at boost rate.  Most of the extract air is from the kitchen, as that's the highest flowing extract duct, even at the trickle ventilation rate, and as our kitchen, utility and downstairs WC all draw fresh air in through the kitchen door, from fresh air feeds in other rooms, the chance of cooking smells escaping is pretty small.

 

The MVHR really is very effective at removing smells.  When we were painting and oiling the woodwork, there would be no trace of any "fresh paint smell" the next morning.  I'm pretty sure this is just down the MVHR being many more times as effective at properly ventilating the house than trickle vents, leaving a window open, or whatever, probably because it's not really affected much by outside conditions and is running all the time.

As ever Jeremy, the voice of reason - thanks very much. 

[Stones]

On 2/18/2017 at 10:21, JSHarris said:

I posted somewhere else about how easy it can be to clean and refurbish the grease and activated carbon filters in a recirculating hood.  I do ours about every six months or so, depending on whether or not it looks like it needs a clean.  It's just a matter of sticking the stainless grease filter mesh in the dishwasher and refilling the carbon filter unit with fresh carbon granules (which can be bought in bulk pretty cheaply from fish pond equipment suppliers).  This works well, and keeps the everything clean around the hob in our current house.

 

@JSHarris I'm assuming it's this stuff you are referring to

 

https://www.ebay.co.uk/i/141423012362?chn=ps&var=440565779051&adgroupid=48942490953&rlsatarget=pla-380368210229&abcId=1128946&adtype=pla&merchantid=7240314&googleloc=1007335&device=c&campaignid=856243387&crdt=0

 

and simply a case of emptying the filter out and refilling?