Is a cooker extractor necessary with MVHR

[SBMS]

With whole house MVHR, is an extractor fan necessary in kitchen area, or does MVHR in the kitchen perform the same function?  We are considering adding MVHR and we currently have specced the kitchen with a ceiling extractor unit, but am hoping we can get rid of this if we add MVHR.

 

[Conor]

You need something to deal with the grease when frying. We're having a recirculating downdraft hob.

 

[joe90]

I installed a recirculating hood over the hob with grease filters and MVHR extract next corner, works well. ?

[ProDave]

Another with a recirculating hood and mvhr.

 

We did use the kitchen for about a year before we installed the hood, it did not seem to cause a problem, but it just looked wrong without it.

[tonyshouse]

We hardly use the hood but when we do it sends cooking smells and more importantly grease and greasy steam outside.

 

not nice in MVHR ducts or in the machine 

[ProDave]

13 minutes ago, tonyshouse said:

We hardly use the hood but when we do it sends cooking smells and more importantly grease and greasy steam outside.

 

not nice in MVHR ducts or in the machine 

But in a house with mvhr you do NOT connect a cooker hood to the mvhr ducts, that would indeed be bad.  You set up the cooker hood to recirculate with a filter.

[joth]

If by "necessary" you mean "legally required per building regs" the answer is a clear "no": so long as the MVHR has a kitchen extract vent with sufficient capacity, there's no obligation to have any kind of hood/air capture/filter for the hob whatsoever. 

Note the general recommendation is to not put the MVHR extract too close to the hob (i.e. not directly over it) to avoid grease heading straight up it.

 

For grease and smell management, we also went with downdraft recirculating hob (Bora Pure-X) with a filter that gets washed in the dishwasher as needed, very easy. 

 

[JohnMo]

We had no cooker hood for about 6 weeks, no issue with smells etc, but we didn't fry.  If you are frying you need something to extract the grease that become airborne.  Otherwise you will be trying to clean your ducts to the MVHR in a year or so.  You also need a filter in the mvhr duct to catch the grease the cooker hood doesn't extract.

[SBMS]

Thanks everyone ?

[saveasteading]

Are there any cooker hoods with an automatic  opening/closing shutter so that the pipe is closed when not in use?

 

Like in some of the flashier wall extraction fans.

[Iceverge]

We Installed one of these.

 

Seems to work ok. 

 

https://www.naber.de/en-thermobox-150-s13027/

[offthepiste]

Still ruminating over how we should handle our kitchen extractor.

 

Research suggests that overhead updraft is better than downdraft, so sort of decision made there.

 

However, given how and what I tend to cook - a lot of fish on top on griddle / bring pan and also under grill - and what I have read about particulates from cooking ... would really like a proper extractor and not a recirculating unit. However, as everyone will know this is an issue with an airtight'ish house and need to balance output and input air supply.

 

@Iceverge post re Naber got me looking their other products .. there is one which looks like it would work.. https://www.naber.de/en-bixo-balancer-waste-and-fresh-air-wall-conduct-s13823/ BUT ... how reliable will this be in the long term??? Either in maintaining the (I guess Bluetooth) pairing between the input & output vents and also the twisting of fabric to make it "airtight" when  extractor not in use.

 

I prefer to keep things simple .. so suspect, unless anyone has a brilliant suggestion .. to go for recirculating.

 

In respect of recirculating extractors did a bit of searching regarding plasma filters and came across this https://www.plasmamadefilters.co.uk so was wondering if it would be possible to retain the normal washable grease filter and then belt and brace it with a plasma filter. I think there may be available extractor hoods which include plasmas but they may be a bit pricey.

 

Also want to minimise grease etc in the MVHR units.

Cheers

Edited January 13, 2022 by offthepiste

[JohnMo]

We have washable carbon filters as well as the grease filters

[joe90]

I have a recirculating hood with grease filters and an MVHR extract in the next corner and had no problems whatsoever and we do fry occasionally.

[Dan F]

On 22/12/2021 at 13:56, joth said:

For grease and smell management, we also went with downdraft recirculating hob (Bora Pure-X) with a filter that gets washed in the dishwasher as needed, very easy. 

 

We have the same one, it actually also has a seconday (carbon?) filter too which can be changed.   Do you have a recirculating kit and/or vent in plinth or does it just extract into void behind cupboards or island?  Ours has been set up to extract into the void in the middle of the island.. 

Edited January 13, 2022 by Dan F

[Iceverge]

2 hours ago, offthepiste said:

airtight'ish house

 

What ACH are you targeting?

 

At 0.31 we still had 49cm2 of holes somewhere. We need to tilt a window to get full extract effectivity at max speed  However on low speeds it works fine just using background leakage. 

 

[Roundtuit]

2 hours ago, offthepiste said:

I prefer to keep things simple ..

Me too.  I put in an overhead extractor vented to the outside.  Using the mvhr seemed more expense and complication than it was worth.  We don't use it very often (occasionally frying, curry night etc), but I always open a window a fraction when I put it on to give it enough air flow.  There's an in-line flap to prevent back draughts. Works for me.

[hb1982]

the level of "small" "grease" generated in cooking is not universal. recirculation hood with carbon and grease filters may work for some people but not everyone. best to speak to friends or to experience hood performance at their place

 

Even for "extraction hood", performance varies a lot. 6" duct with 900mm wide hood minimum 500 m3/hr  is the minimum standard in my opinion (1.5m x 3.0m x 2.5m zone @ 40ACH x 1.1 leakage). 

[joth]

On 13/01/2022 at 17:00, Dan F said:

 

We have the same one, it actually also has a seconday (carbon?) filter too which can be changed.   Do you have a recirculating kit and/or vent in plinth or does it just extract into void behind cupboards or island?  Ours has been set up to extract into the void in the middle of the island.. 

Same: no special kit, extracts into the island central void and then down under the units and comes out through the plinth, about 6m perimeter so fairly low flow rate all round it.

[Pocster]

Recirculating extractor also with MVHR. Also I *believe* it's better to have a down extractor..... ( waits for correction )

[Adsibob]

I ordered an extractor hood with a recirculation kit because I knew that we couldn't pierce the envelope of the house as this would compromise air tightness required for MVHR. But now we're coming to installing the hood, I'm wondering where the air which the recirculation kit pushes out should go? My wall units are quite tight to the ceiling, with only an 18mm gap above them. Is it fine to push the air out there from where it will re-enter the kitchen? That run of units is about 4.2m wide, so the area which would act as a sort of vent back into the kitchen is 18 x 4200 = 75,600 mm2.

The other alternative is that after the air has gone through the recirculation filter we pass it into a duct that then travels about 2m until it can vent through a normal round hole into the kitchen instead of into the rectangular 4200 x 18 makeshift hole. Which is likely to be less noisy? 

The builder is asking why I don't just drill a hole through the wall and fit a one way valve, but I'm sure that would mess up the pressure balance, though as some have commented above, there might be ways around this.

[joe90]

Usually the recirculating hoods exit the air from vents either side of the vertical tube! Do you have a pic of your hood?

[Bitpipe]

We positioned a kitchen MVHR extract in-between the ovens and the hob (they are opposite each other), plus a recirculating hood with grease and carbon filter.

 

There is another MVHR extract in corner of kitchen, conveniently located over the toaster in which I burn bread with alarming regularity.

 

Agree that if there is some really smelly cooking going on, the kitchen window gets opened on tilt.

 

All seems to work fine. 

[hb1982]

1 hour ago, Adsibob said:

I ordered an extractor hood with a recirculation kit because I knew that we couldn't pierce the envelope of the house as this would compromise air tightness required for MVHR. But now we're coming to installing the hood, I'm wondering where the air which the recirculation kit pushes out should go? My wall units are quite tight to the ceiling, with only an 18mm gap above them. Is it fine to push the air out there from where it will re-enter the kitchen? That run of units is about 4.2m wide, so the area which would act as a sort of vent back into the kitchen is 18 x 4200 = 75,600 mm2.

The other alternative is that after the air has gone through the recirculation filter we pass it into a duct that then travels about 2m until it can vent through a normal round hole into the kitchen instead of into the rectangular 4200 x 18 makeshift hole. Which is likely to be less noisy? 

The builder is asking why I don't just drill a hole through the wall and fit a one way valve, but I'm sure that would mess up the pressure balance, though as some have commented above, there might be ways around this.

 

I am a strong believer that grease, smell and moisture should be discharge to the atmosphere in the most direct way.

If recirculation is preferred to match with MVHR installation in an air-tight house, it should be done again to minimise pressure drop; discharge air to open air (avoid damp); best possible filtration with regular maintenance. 

 

[Adsibob]

1 hour ago, joe90 said:

Usually the recirculating hoods exit the air from vents either side of the vertical tube! Do you have a pic of your hood?

My hood is concealed within the wall units above the hob. It is a 90cm wide x 30cm deep unit designed to be concealed within such cabinets, as long as they are at least 92cm wide by 31cm deep.