Is a cooker extractor necessary with MVHR

[joe90]

13 minutes ago, Adsibob said:

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.

So where does your hood vent to? Is it a recirculating type?

Edited February 2, 2022 by joe90

[Adsibob]

2 hours ago, joe90 said:

So where does your hood vent to? Is it a recirculating type?

Well it’s a normal (albeit bloodyexpensive Novy) hood, which has an optional accessory pack which enables it to be converted from one that extracts out of the house to one that recirculates through a carbon filter. 
the issue I have is that if I don’t extract it out of the house, I’m not sure where the exhaust air should be vented to. Here is a diagram showing the concealed extractor within my kitchen wall cupboards. Each cupboard is 500mm wide, so the distance from the centre of the concealed hood to the area above the fridge where the MVHR extract is, is about 2.5 to 2.75m. 

Option 1: I could take the wall units down, cut a hole in the ceiling above them and get a duct to take the air to the area above the fridge, where it would then get sucked up by the MVHR pipe

 Option 2: just cut a hole at the top of the kitchen wall cabinet housing the hood and recirculating accessory kit, and let it extract into that 18mm high gap, which I mentioned in my earlier post. The air would make its way into the kitchen and eventually find its way to the MVhR duct above the fridge.

Option 3: cut a hole through the wall behind the kitchen units, which is an external wall, and extract there. The only benefit of that is that I can get about £90 for my recirculating kit, as I won’t need that. But the downside is the air tightness issue.

 

Just a reminder that options 1 and 2 both include the recirculation of the air through the carbon filter in the recirculation accessory kit, so as long as the carbon filters are cleaned fairly regularly, the air output by the hood into the kitchen should always be clean and smell free.

Edited February 2, 2022 by Adsibob

[joe90]

@Adsibob Ah, do you have a link to the model you bought?

[Adsibob]

12 minutes ago, joe90 said:

@Adsibob Ah, do you have a link to the model you bought?

Yes:

• this is the hood: https://www.novy.com/en-gb/products/cooker-hoods/build-in-cooker-hoods/fusion-pro/8740/
• and this is the recirculating filter: https://www.novy.com/en-gb/products/accessories/recirculation-accessories/recirculation-kit/8740400/

Just reading the instructions on the hood now. Unhelpfully, it just says:

 

Recirculation If you choose recirculation, Novy offers a monoblock recirculation filter which is placed in the hood.

The monoblock filter is placed directly behind the grease filter. The exhaust grill to let the filtered air back into the kitchen must be provided by you.

Basic kit monoblock filter (without outlet box) 8740400 [this is the one I bought]

The exhaust grill to let the filtered air back into the kitchen must be provided by you. Minimum net opening of the exhaust grill: 177 cm².

 

So actually, the very long and thin space I have above the units is big enough to provide that 177cm2 as it measures 1.8cm by 400cm or so. So about 720cm2. But query whether the aerodynamics of such a narrow slit will be problematic/noisy.

Edited February 2, 2022 by Adsibob

[joth]

43 minutes ago, Adsibob said:

Option 1: I could take the wall units down, cut a hole in the ceiling above them and get a duct to take the air to the area above the fridge, where it would then get sucked up by the MVHR pipe

..

Option 3: cut a hole through the wall behind the kitchen units, which is an external wall, and extract there. The only benefit of that is that I can get about £90 for my recirculating kit, as I won’t need that. But the downside is the air tightness issue.

 

It's not just that the external outlet will defeat all your airtightness work, but you need a balanced flue of somesort, or some other hole in the house to allow a corresponding inward airflow. Wherever you send the dirty expelled air to, you need to think about the return route for replacement air to makes its way back around and into the intake side of the vent.

 

Really in an airtight house I think option 2 is your only bet. Perhaps you can combine it with Option 1 to a degree - vent it out over the top of the units, and also through to behind the fridge. Or vent it out over the units and also put a concealed hole above the units into the ceiling, and be prepared to cut another ceiling void outlet grill somewhere if needed?

 

On level 3 your hood is about the same as our Bora Pure X max (548 m3/h) and we have that venting out via about 8m long x 10mm tall  gap around the island and it doesn't make any noticeable noise -- just aware of it from the cool draft  on bare toes.  Remember this is only an issue when the hood itself is on full whack, which is not silent by any stretch, and you probably have something fierce boiling/frying at that time too, so it's not exactly going to risk disturbing an otherwise library-like atmosphere.

 

Edited February 2, 2022 by joth

[Adsibob]

Thanks @joth and @joe90 that's helpful. Discussing with my other half she reminded me that we had planned to close off that 18mm gap to avoid the area becoming a dust trap. So the only way to do option 2 and also close off the gap would be to fit something like this https://www.yesterhome.com/products/black-aluminium-large-grill-380mm?currency=GBP&variant=39424828735572&utm_medium=cpc&utm_source=google&utm_campaign=Google Shopping&gclid=Cj0KCQiA9OiPBhCOARIsAI0y71DyU-1sX52aO1Znry1Klhf32UVEUUa3ehKV7izVJU9BMsHP4rMIUZsaAlzmEALw_wcB which I would spray paint to match the colour of the kitchen units. Would that mitigate the dust issue though?

 

Discussing this further I realised that I had forgotten that we had moved the MVHR outlet. It's actually slightly closer to the hob area, albeit on a different wall that is perpendicular to the wall where the hob is. This creates the possibility of a fourth option, which is to just get the duct to redirect the air by 180 degrees so that it comes out of the adjacent kitchen unit on the underside of the unit. This won't be visible because there is a pelmet that conceals our over-worktop lighting, so it will also conceal the extract if we were to fit it there. It would look like this: 

 

The obvious downside of this is that we lose space in the adjacent cupboard, but the units are 31cm deep and the duct is a 15cm diameter one, so we would only lose half the depth of the unit where the duct is.

 

Is another downside that I create some sort of vortex of air going around and around in a circle into my hob extractor, out of it and then back into it, and that vortex in some way messes with the MVHR currents?

Edited February 2, 2022 by Adsibob

[joe90]

Ooh er, a real dilemma!!!, yes that grill would be a good way of filling the gap but like you I wonder the effect of moving air into that gap. Right, thinking outside the box!what if you created an “exhaust manifold” as per diagram below, aluminium pop riveted to disperse the air into that top void ?? you can make it what size you see fit (perhaps my drawing is a bit big) you will only loose a small portion of those two cupboards and nothing to be seen externally.

[hb1982]

On 02/02/2022 at 17:17, Adsibob said:

Yes:

• this is the hood: https://www.novy.com/en-gb/products/cooker-hoods/build-in-cooker-hoods/fusion-pro/8740/
• and this is the recirculating filter: https://www.novy.com/en-gb/products/accessories/recirculation-accessories/recirculation-kit/8740400/

Just reading the instructions on the hood now. Unhelpfully, it just says:

 

Recirculation If you choose recirculation, Novy offers a monoblock recirculation filter which is placed in the hood.

The monoblock filter is placed directly behind the grease filter. The exhaust grill to let the filtered air back into the kitchen must be provided by you.

Basic kit monoblock filter (without outlet box) 8740400 [this is the one I bought]

The exhaust grill to let the filtered air back into the kitchen must be provided by you. Minimum net opening of the exhaust grill: 177 cm².

 

So actually, the very long and thin space I have above the units is big enough to provide that 177cm2 as it measures 1.8cm by 400cm or so. So about 720cm2. But query whether the aerodynamics of such a narrow slit will be problematic/noisy.

 

£159 for two black filter blocks... I wonder what they are made of....

[Adsibob]

22 minutes ago, hb1982 said:

 

£159 for two black filter blocks... I wonder what they are made of....

That's the undiscounted price. I got about 35% off that, although still a rip off.

Edited February 3, 2022 by Adsibob