Induction downdraft hobs requirements (Bora etc)

[SuperJohnG]

Finalising my building warrant drgs and my architect has a duct going from Island to external for the Hob. This would need to pass through my insulated slab and I don't fancy it. 

 

I assumed it would recycle below the hob and then vent below the island to the room. I'm sure this is the case, but can someone confirm this is ok and that it works well that way? 

 

Bora, Neff, Siemens, Nikola Tesla etc. 

 

It's probably quite important as I have high levels of airtightness also and MVHR so don't want an external duct. 

 

thanks in advance. 

[ryder72]

Yes it works. Stay clear of the BSH products. Stick with the specialist brands.

And ensure you have an extract duct above the hob.

[Conor]

I'm hoping to use a recirculating Elica in my kitchen... I'm assuming that the MVHR extract in the kitchen will comply with the min BC regs of 13l/s. I'll be doubling up regardless - one above the island near the hob, and another above the sink, and a supply at the start of the kitchen area to have airflow from the living area to the kitchen to help keep smell contained. Others here have done that and it seems to work well.

Edited November 10, 2020 by Conor

[SuperJohnG]

13 minutes ago, ryder72 said:

Yes it works. Stay clear of the BSH products. Stick with the specialist brands.

And ensure you have an extract duct above the hob.

Thanks. I am planning a duct above the hob - but I have vaulted ceilings, so it will be as close as I can get, but sure how effective. 

 

11 minutes ago, Conor said:

I'm hoping to use a recirculating Elica in my kitchen... I'm assuming that the MVHR extract in the kitchen will comply with the min BC regs of 13l/s. I'll be doubling up regardless - one above the island near the hob, and another above the sink, and a supply at the start of the kitchen area to have airflow from the living area to the kitchen to help keep smell contained. Others here have done that and it seems to work well.

That's is my plan to to have opposite sides of room also. why an extract above sink? 

 

 

[ryder72]

I havent felt the need to have a duct extract above the sink. The hob one is essential though.

 

[Conor]

14 minutes ago, SuperJohnG said:

Thanks. I am planning a duct above the hob - but I have vaulted ceilings, so it will be as close as I can get, but sure how effective. 

 

That's is my plan to to have opposite sides of room also. why an extract above sink? 

 

 

 

To handle all the steam when pouring out hot water etc from washing up and opening the dishwasher. Plus we've a baby bottle steriliser that kicks out a lot of steam. And the sink is a fair distance away from the hob (I'll have prep sink on the island beside the hob). Kitchen is over 6m long so almost treating it as two rooms.

[Dan F]

Careful with putting an MVHR extract directly above a BORA extractor as it can impact effectiveness.

[joth]

Similarly, we've gone for MVHR extract above the sink & dishwasher (against a wall also containing the ovens), and Bora recirculating hob in the island about 2m away from the sink.

The Bora will vent out under the plinth all around the island, which has about 9m perimeter, so no specific direction or focus for the draft coming out of it.

 

[SuperJohnG]

3 hours ago, Dan F said:

Careful with putting an MVHR extract directly above a BORA extractor as it can impact effectiveness.

By above - it's maybe 3.5-4m above. 

[Dan F]

46 minutes ago, SuperJohnG said:

By above - it's maybe 3.5-4m above. 

In your case it'd be fine I'd imagine.   But with 2.5m ceiling heights, where MVHR is just 1.5m above hob,  i've been told it can interfere with effectiveness.

Edited November 10, 2020 by Dan F

[SuperJohnG]

I'd maybe plan my MVHR vent above the sink then as it'll minimise the run. I'll need to go figure out how many I need for that room. 

[Dave Jones]

ive not done this, but assume with a block and beam floor you could vent into the void beneath it ?

[SuperJohnG]

51 minutes ago, Dave Jones said:

ive not done this, but assume with a block and beam floor you could vent into the void beneath it ?

I wouldn't see why not as that void is vented to atmosphere, hence condensation wouldn't be an issue 

[Pete]

8 hours ago, joth said:

Similarly, we've gone for MVHR extract above the sink & dishwasher (against a wall also containing the ovens), and Bora recirculating hob in the island about 2m away from the sink.

The Bora will vent out under the plinth all around the island, which has about 9m perimeter, so no specific direction or focus for the draft coming out of it.

 

We have exactly the same setup, have not tested it yet as not moved in! ( hopefully before xmas)

[ryder72]

I have a venting hob with an MVHR duct above it. It doesnt make a blind bit of difference to the performance of the hob. Your venting hob is going to work by accelerating air flow to a speed way higher than what the MVHR does. A recirculating hob will vent the extracted air back into the room and the impact of this air flow  which you can feel on your feet has made no impact on the ability of the MVHR to ventilate the room effectively.

If anything your hob will affect the MVHR and not the other way round.

[Dan F]

9 hours ago, ryder72 said:

I have a venting hob with an MVHR duct above it. It doesnt make a blind bit of difference to the performance of the hob. Your venting hob is going to work by accelerating air flow to a speed way higher than what the MVHR does. A recirculating hob will vent the extracted air back into the room and the impact of this air flow  which you can feel on your feet has made no impact on the ability of the MVHR to ventilate the room effectively.

If anything your hob will affect the MVHR and not the other way round.

 

Good to know!  We've had both MVHR designer and kitchen designer tell us to avoid avoid using a slot difusor above island, which is where we'll have Bora hob.

 

 

[ryder72]

17 hours ago, Dan F said:

 

Good to know!  We've had both MVHR designer and kitchen designer tell us to avoid avoid using a slot difusor above island, which is where we'll have Bora hob.

 

 

I am not expert at this, but when you consider that most hobs will do extraction rates from 275m3/hr to 650m3/hr (4500-10000 l/min). Compare this to your MVHR vent which is doing a tiny fraction of this flow rate.

If anything the extractor could affect the flow of the MVHR and definitely not the other way round.

I have most certainly not seen anything obviously detrimental and most odours are completely cleared in 30 min in a very open plan kitchen.

[Dan F]

9 hours ago, ryder72 said:

I am not expert at this, but when you consider that most hobs will do extraction rates from 275m3/hr to 650m3/hr (4500-10000 l/min). Compare this to your MVHR vent which is doing a tiny fraction of this flow rate.

 

Our kitchen has 60m3/hr extract specificed, so lot less but not quite tiny.   Think we'll try to keep it from directly over the hob, but other than that not worry too much..

[john0wingnut]

I have a venting Hob currently, and as part of the extension Im planning, we are putting MVHR in.

 

Initial MVHR plan has extract planned between the sink and hob, and we have been advised to change our overhead hood to a recirculating one, or fit a downdraft recirculator in the island, as if we had one venting to the outside it would mess with the MVHR system balance.

[Conor]

15 hours ago, john0wingnut said:

I have a venting Hob currently, and as part of the extension Im planning, we are putting MVHR in.

 

Initial MVHR plan has extract planned between the sink and hob, and we have been advised to change our overhead hood to a recirculating one, or fit a downdraft recirculator in the island, as if we had one venting to the outside it would mess with the MVHR system balance.

It will mess with balance. But only for the time the extractor is on. Unless you do a LOT of cooking, that will only be a few mins a day typically. Wouldn't worry too much.

[eandg]

On 10/11/2020 at 12:05, SuperJohnG said:

Finalising my building warrant drgs and my architect has a duct going from Island to external for the Hob. This would need to pass through my insulated slab and I don't fancy it. 

 

I assumed it would recycle below the hob and then vent below the island to the room. I'm sure this is the case, but can someone confirm this is ok and that it works well that way? 

 

Bora, Neff, Siemens, Nikola Tesla etc. 

 

It's probably quite important as I have high levels of airtightness also and MVHR so don't want an external duct. 

 

thanks in advance. 

A builder has recommended 'trunking' from the electrics coming in (approx 10m distance from our island) rather than coming through the slab again, though we will have UFH and I'm concerned about interfering with the runs. Have you looked at that option?

[puntloos]

Reviving this one for a moment.

 

Can someone explain why ducting hot air from the hob extractor directly into MVHR is a bad idea? Or is it just hard to achieve since most people can't easily get a MVHR duct to an island without tearing up their floors?

 

(as an aside, quooker also recommends some way of cooling their gear, rather than sealing it into a box..)

 

[pdf27]

18 minutes ago, puntloos said:

Can someone explain why ducting hot air from the hob extractor directly into MVHR is a bad idea? Or is it just hard to achieve since most people can't easily get a MVHR duct to an island without tearing up their floors?

You really don't want grease in the MVHR heat exchanger.

[puntloos]

22 minutes ago, pdf27 said:

You really don't want grease in the MVHR heat exchanger.

 

Fair, but if the filtered air from the extractor still contains grease (I'm sure it does), is there a big difference between directly extracting it and just extracting the air from the kitchen in general? Perhaps beaming it into the kitchen first allows more of the grease to settle on 'the rest of the kitchen'....

[ryder72]

3 hours ago, puntloos said:

Reviving this one for a moment.

 

Can someone explain why ducting hot air from the hob extractor directly into MVHR is a bad idea? Or is it just hard to achieve since most people can't easily get a MVHR duct to an island without tearing up their floors?

 

(as an aside, quooker also recommends some way of cooling their gear, rather than sealing it into a box..)

 

I am probably not using the right terminology here, but whatever volume of air the extractor moves will be within the room. Piping that volume of air into the MVHR extract vent will sure throw the system out of balance.