MVHR cooker hood idea

[woodman]

For some time, I've been considering the best way to integrate my cooker hood during MVHR installation. Having read the good words on here, it seems that direct integration from hood to MVHR is a BAD IDEA, so I've come up with this- Comments appreciated.

My situation is this:

1) Large kitchen diner with induction hob plus 600mm  externally vented extractor hood. There is no room to replace the extractor  with a wider hood due to cabinets being in place. The hood does not cope with cooking smells/steam particularly well.

2) Cooker hood is too noisy. It currently vents externally. MVHR install requires changing to internal vent, which is likely to further increase noise levels and cooking smells

3) I don't want to link the MVHR and  cooker hood ducts. 

 

However, the family bathroom is behind the kitchen/diner cooker wall. (loft is above) 

The family bathroom will have a high level of MVHR extraction, (higher extraction than the  MVHR extract vent adjacent to the kitchen area) as extract noise is not greatly important in the bathroom.

As part of the MVHR install, I'm removing 4  fairly new ducted fans from existing bathrooms. If I remember correctly, each of these have a capacity of around 240m3/hr. And they can be re-used...

 

I'm considering :

A) removing existing ducting and fan from the extractor hood.

b)  Install a 150mm duct between the cooker hood and bathroom, exiting  fairly close to the MVHR vent. This vent to be fitted with a filter

c) Mount  2 of my  'redundant' ducted fans in parallel into this duct. Fans to be operated by the existing cooker hood switch assembly. (I need to check out current draw first)

d) Renew charcoal filters on the cooker hood, possibly adding further filters within the  unused hood motor space. 

e) Connect the cooker hood to the MVHR such that hood usage  boosts the MVHR .

 

Whilst not perfect, I think this 'indirect connection' will:

1) improve efficiency of extraction of cooking smells. Better extract capability  resulting from significantly lower  (shorter) duct losses.  Possibility to add further filtering within the empty cooker hood to reduce odour transfer to bathroom. (There will also be an MVHR kitchen extractor vent in the area) 

2) Significant reduction of fan motor noise in the kitchen/diner as the ducted fans will be in the loft, outputting to the bathroom which is less noise sensitive. 

3)  Prevent  grease contamination of the MVHR system as grease will be trapped within the cooker hood/duct filter assembly. 

4) I'm hoping that additional activated charcoal filters within the  cooker hood will prevent cooking smells reaching the bathroom.

 

I realise that the amount of air I'll be transferring from the kitchen to the bathroom will exceed the extraction capabilities of the bathroom MVHR, however gaps below the door should take care of this.  

Comments welcome!!

 

[Bitpipe]

Seems very convoluted.

 

We have a dedicated mvhr extract (double ducted) about 1m in front of the cooker hood (which is a recirculating unit). It’s also midway between the wall mounted oven to catch extract from those too.

 

Kitchen has separate general purpose extract (probably overkill).

 

Your risk is introducing strong cooking smells into bathroom which could be quite unpleasant. 
 

The core issue here seems to be the performance of your extractor - sounds like that needs an upgrade.

[Conor]

5 hours ago, woodman said:

 

2) Cooker hood is too noisy. It currently vents externally. MVHR install requires changing to internal vent, which is likely to further increase noise levels and cooking smells

 

 

Not true. You can still vent externally. Yes, you will be dumping heat to the outside, and you will imbalance the MVHR during operation. However, as my friend that designs and installs MVHRs pointed out, it's normally only for a few minutes per day, so doesn't have a significant effect on air quality over 24hours. I would suggest ripping out the existing extractor motor  (keep the hood if you want) and fitting an externally mounted centrifugal fan, like one of the Monsoon ranges from Fastlec. This is exactly what I have in my house, and when fan is on full 600m3/hr mode, is virtually silent.

[Visti]

How about extractor hob? a closed system that uses carbon filters and doesnt need venting. No need to integrate and mess with the MVHR.

[tanneja]

On 12/11/2019 at 14:47, Conor said:

 

Not true. You can still vent externally. Yes, you will be dumping heat to the outside, and you will imbalance the MVHR during operation. However, as my friend that designs and installs MVHRs pointed out, it's normally only for a few minutes per day, so doesn't have a significant effect on air quality over 24hours. I would suggest ripping out the existing extractor motor  (keep the hood if you want) and fitting an externally mounted centrifugal fan, like one of the Monsoon ranges from Fastlec. This is exactly what I have in my house, and when fan is on full 600m3/hr mode, is virtually silent.

Hi @Conor, where in the vent circuit would there be airtightness valve in operation when the hood is turned off?  I can't see it written but would it be safe to assume the external fan has a type of one way valve that is relatively airtight when not in operation? 

[Conor]

2 hours ago, tanneja said:

Hi @Conor, where in the vent circuit would there be airtightness valve in operation when the hood is turned off?  I can't see it written but would it be safe to assume the external fan has a type of one way valve that is relatively airtight when not in operation? 

The fan I used didn't. I just had a flap damper which was useless. If I was doing it again I'd go for an actuated damper. At that point I'd ask my spark to figure it out and wire it up for me ?

[dpmiller]

I put a nice rubber-sealed gravity flap in and I can only think of a couple of occasions on a really windy day where it's attempted to lift off it's seal. Otherwise it sits there and isn't affecting airtightness markedly.

[tanneja]

3 hours ago, dpmiller said:

I put a nice rubber-sealed gravity flap in and I can only think of a couple of occasions on a really windy day where it's attempted to lift off it's seal. Otherwise it sits there and isn't affecting airtightness markedly.

Out of interest how do you know that?  Do you sit outside and watch it?  I would be paranoid it was misbehaving when I has my back turned.

 

 

[dpmiller]

the kitchen isn't fitted out yet and the valve is hanging from the duct in the ceiling (it's for an Island hood) with a large bag taped over it. The bag never fully inflates or deflates and as I said only extremely rarely with unusual wind directions will the flap clunk. I should add that I've the MVHR set towards positive pressure to safely deal with the not-yet fitted boiler stove, and that would make the valve even more sensitive...

 

this kinda thinghttps://www.amazon.co.uk/Klimapartner-100-line-Backdraught-Extractor/dp/B011INHF5A/ref=sr_1_14?dchild=1&keywords=passive+flap&qid=1627639391&rnid=1642204031&s=diy&sr=1-14

but with a thin smear of silicone over the central pivot.

[Adsibob]

I too am considering venting my hob extractor outside. I know it isn’t the technically perfect thing to do with an MVHR system, but it avoids a lot of issues for me. Our Hob is right by an external wall. 

I’m wondering how @dpmiller, @woodman and @Conor got on with their installs. Do you all vent outwards even though you have MVHR? 

[hb1982]

7 minutes ago, Adsibob said:

I too am considering venting my hob extractor outside. I know it isn’t the technically perfect thing to do with an MVHR system, but it avoids a lot of issues for me. Our Hob is right by an external wall. 

I’m wondering how @dpmiller, @woodman and @Conor got on with their installs. Do you all vent outwards even though you have MVHR? 

 

How air tight is your house?

Otherwise can you provide make up air via trickle vent; openable windows or dedicated air valve ; weighted damper etc.

 

In some high end residential I specified, we put in automatic make-up air damper triggered by the extractor via a current transformer. 

[Adsibob]

22 minutes ago, hb1982 said:

 

How air tight is your house?

Otherwise can you provide make up air via trickle vent; openable windows or dedicated air valve ; weighted damper etc.

 

In some high end residential I specified, we put in automatic make-up air damper triggered by the extractor via a current transformer. 

It is fairly airtight , although not to passive standard. We have installed Tecson Vana tape at every junction between walls and windows/doors as well as specifying zero trickle vents on all windows/doors. 
 

I’m interested in the automatic make-up air damper you mention. Does that open a vent to allow air in when you turn on the extractor? Link?

Edited February 6, 2022 by Adsibob

[hb1982]

14 minutes ago, Adsibob said:

It is fairly airtight , although not to passive standard. We have installed Tecson Vana tape at every junction between walls and windows/doors as well as specifying zero trickle vents on all windows/doors. 
 

I’m interested in the automatic make-up air damper you mention. Does that open a vent to allow air in when you turn on the extractor? Link?

 

That was a specification for high-end residential to avoid recirculation hood.

TBH it sounds like a commercial type installation but could be DIY. A 4"/6" motorised damper with belimo actuator, normally closed, drive open. 230V AC power supply, a current transformer to sense the extractor operation and give power to drive open the Belimo actuator.

May be around £ 200 to 250 on materials?

 

A less sophisticated version is a weighted shutter to control the make-up air. 

Make sure the mark-up air duct is properly insulated to avoid condensation. 

 

Your kitchen extractor should be fitted with wall shutter with weight backdruaght damper in external wall face as well. Blauberg sells some good looking stainless version (I used plastic only in my house extension but added weight to the shutter to make it less flippy). 

I don't have MVHR therefore rely on make-up air via trickle vents. 

 

[Adsibob]

57 minutes ago, hb1982 said:

 

That was a specification for high-end residential to avoid recirculation hood.

TBH it sounds like a commercial type installation but could be DIY. A 4"/6" motorised damper with belimo actuator, normally closed, drive open. 230V AC power supply, a current transformer to sense the extractor operation and give power to drive open the Belimo actuator.

May be around £ 200 to 250 on materials?

 

A less sophisticated version is a weighted shutter to control the make-up air. 

Make sure the mark-up air duct is properly insulated to avoid condensation. 

 

Your kitchen extractor should be fitted with wall shutter with weight backdruaght damper in external wall face as well. Blauberg sells some good looking stainless version (I used plastic only in my house extension but added weight to the shutter to make it less flippy). 

I don't have MVHR therefore rely on make-up air via trickle vents. 

 

I googled belimo and found a bunch of actuators, but I confess I’m not sure how these work. How are they different to the product @dpmiller linked to: https://www.amazon.co.uk/Klimapartner-100-line-Backdraught-Extractor/dp/B011INHF5A/ref=sr_1_14?dchild=1&keywords=passive+flap&qid=1627639391&rnid=1642204031&s=diy&sr=1-14

 

if I installed this Klimapartner I would solve the problem of keeping the external vent closed when not in use, but I wouldn’t solve the issue of having a way to bring air into the kitchen from outside to keep the air pressure in that room balanced. Is that What the belimo actuators could do? If so how do they work?

[JohnMo]

If your extract is performing poorly, either it's a rubbish extractor, or it is positioned too high on the wall.  Our new kitchen was installed a couple of months ago, our extractor performed rubbish.  Read the instructions and it said to install 450 to 500mm above hob.  Measured and it was at 750mm.  Rang company and they stated that the dimensions they alway use.  Got them back to install as per instructions and it works great. 

 

Recirculation or extract outside your call.

[Adsibob]

6 minutes ago, JohnMo said:

If your extract is performing poorly, either it's a rubbish extractor, or it is positioned too high on the wall.  Our new kitchen was installed a couple of months ago, our extractor performed rubbish.  Read the instructions and it said to install 450 to 500mm above hob.  Measured and it was at 750mm.  Rang company and they stated that the dimensions they alway use.  Got them back to install as per instructions and it works great. 

 

Recirculation or extract outside your call.

Mine hasn't been installed yet, but I doubt it will perform badly. It is the most expensive appliance I have bought for the kitchen and reviews incredibly well. It's also being installed well within the recommended distance from the hob. The only issue is whether it will unbalance my MVHR by extracting directly outside.

[Temp]

6 hours ago, Adsibob said:

The only issue is whether it will unbalance my MVHR by extracting directly outside.

 

How much of the time will it be running?

 

 

[hb1982]

8 hours ago, Adsibob said:

I googled belimo and found a bunch of actuators, but I confess I’m not sure how these work. How are they different to the product @dpmiller linked to: https://www.amazon.co.uk/Klimapartner-100-line-Backdraught-Extractor/dp/B011INHF5A/ref=sr_1_14?dchild=1&keywords=passive+flap&qid=1627639391&rnid=1642204031&s=diy&sr=1-14

 

if I installed this Klimapartner I would solve the problem of keeping the external vent closed when not in use, but I wouldn’t solve the issue of having a way to bring air into the kitchen from outside to keep the air pressure in that room balanced. Is that What the belimo actuators could do? If so how do they work?

 

I hope the attached makes sense to you.

A standard hood extraction of 150l/s (good quality 900mm hood) is not small for an air tight house. 200mm duct is recommended, 150mm is the absolute minimum. 

 

 

Edited February 6, 2022 by hb1982

[Adsibob]

@hb1982 thanks so much!

[Conor]

12 hours ago, Adsibob said:

I too am considering venting my hob extractor outside. I know it isn’t the technically perfect thing to do with an MVHR system, but it avoids a lot of issues for me. Our Hob is right by an external wall. 

I’m wondering how @dpmiller, @woodman and @Conor got on with their installs. Do you all vent outwards even though you have MVHR? 

I've gone for recirculating. Yet to install the kit (first week in the house) and 100% sure it'll do the job.

[bob the builder 2]

HI All

 

Just following this thread - would be interested to hear if the a recirculating extractor hob and MVHR positioned above the kitchen island worked out ok in terms of performance and smells !

 

Many thanks

 

bob 

[JohnMo]

We have almost stopped using the recirc extract, just put the MVHR on boost job done.  Only really use for smelly cooking.

[Bitpipe]

38 minutes ago, bob the builder 2 said:

HI All

 

Just following this thread - would be interested to hear if the a recirculating extractor hob and MVHR positioned above the kitchen island worked out ok in terms of performance and smells !

 

Many thanks

 

bob 

 

It's what we have, seems to work fine.

[Russdl]

We have a recirculating extractor which vents down by the kick board a few feet away from the hob (after going through grease and charcoal filters) in line with an MVHR vent in the ceiling above. 
 

The extractor does its own thing regarding speeds, run on time etc. We never boost the MVHR. It all works very well. 
 

 

[Adsibob]

It seems i'm the odd one out as I'm not happy with the outcome of our hob extractor. We've been living in our house since early May and cook most nights. We have a very expensive Novy extractor fitted directly above our induction hob, probably only 55cm distance between the hob and the extractor. It can vent outside, but as we have MVHR we bought the carbon filter recirculation kit and so it just vents out the bottom of the adjacent wall unit, onto the worktop that is about 50cm to the right of the hob. It's very powerful but a bit noisy unfortunately, which is a shame because the reason we decided to splash out £1500 on a Novy hood and recirculation kit was because it reviewed very well as one of the quietest extractor hoods on the market. I'm now realising that as most of the noise comes from the outlet, rather than the extractor fan itself, if this vented out of the house (which would be easy for us to do as the hob is against an external wall) instead of directly onto our kitchen worktop it would be very quiet. Another gripe is that the instructions for the carbon recirculation filter recommend leaving the extractor running for 10 minutes after cooking so that the filter gets cleaned. The default settings actually run it for another 10 minutes after you switch it off, though this can be overridden by pressing the off button again.

 

In terms of smells, if somebody is cooking, even though the Novy is on, I can smell food as I walk down our stairwell, which is at the opposite end of the house from the hob. The bottom of the stairs is probably about 9 or 10m away from the hob, although it's all open plan so no barrier in between those two points.

 

Overall, very disappointed with the performance in terms of smell management and noise.

 

MVHR boost will clear the smell pretty quickly, and we have fitted a boost button right by the hob for this reason, but I didn't want to rely on MVHR when the Novy was so bloody expensive. An elica hood would have cost half as much or even less.

 

Seriously considering ruining the air tightness of our house and drilling through the wall to just vent outwards as this will negate most of the noise and probably improve smell extraction as I can't believe the carbon filter is filtering 100% of the smell, otherwise I wouldn't smell it on the other side of the house.

Edited August 12, 2022 by Adsibob