Ducting extractor hob on a kitchen island to outside wall

[CJER]

We are currently renovating our ground floor and adding an extension on.

 

We currently have a thick concrete sub floor in the existing house as was built in the 80's, with no insulation, that we are taking down to then build back up, adding celotex 90mm and 65mm screed with UFH too which will match the new extension that the room will be part of.

 

We have been advised its best to duct the hob fumes/moisture out of the house, rather than recirculating, due to also having a wood log burner in the room and a MVHR, but have seen a lot of reading around the best way to do it.

 

My two main questions are (but will take any extra advice!)l

 

1. What happens to the moisture that condenses and can 'pool' in the duct if we're going vertically down through the island, through the floor under the island (beneath screed and insulation), underneath the floor to the external wall (approx 3 metres from duct entry) and vertically back up and out of the external wall?

2. Does the duct run under block wall and up through the cavity (then out the brick wall below DPC) or behind what will be tall kitchen cabinets?

[Conor]

Recirculating kit if you have an MVHR. I don't know who has been advising you, but they would be against the current consensus. 

 

For the floor, put in 100mm insulation with 50mm liquid screed. I'd say 100mm sheets are easier to come by and cheaper than 90mm anyway.

 

I assume the wood burner is room sealed with it's own air supply?

Edited 20 hours ago by Conor

[CJER]

We were told the MVHR (Venti Fluxo) was to be by the log burner on the opposite side of the room just to recirculate air and if it needs to draw from the room, also a generally good feature to recirculate what will be a well used room.

 

This was on the basis of the log burner being under 5kw without air supply, but since meeting with a HETAS supplier and fitter for the burner, they said they would fit it with its own air supply due to the room having an extractor of some sort (hob) anyway, not sure if this then makes the venti fluxo redundant and unnecessary?

 

The concern with a recirculating was it just isnt as efficient removing grease/moisture as a recirculating.

[Nestor]

@Conor is correct.

We have MVHR in an airtight* new build. It's great, works a treat in the background.

Just the extract and supply in a 60sqm kitchen / dining room, again not an issue.

Personally, If I did it again I would fit kitchen extract to vent outside but inaccessible ducting could be an issue. 

Recirculating hob should be enough and wood burner needs its own sealed air supply.

* Draughty catflap.

 

 

[dpmiller]

regardless of it being room-sealed I don't believe you can have a woodstove in a room which has an extractor of any kind. Read the B-Regs very closely for your jurisdiction... 

[JohnMo]

This sounds like a can of worms. 

 

If you have MVHR you really need external only air supply to stove.

 

As mentioned extract in same room isn't allowed. Extracting hood will just lead to room depressurised and the stove spilling combustion air into the room as soon as door is opened. Even if you have hood in recirculation mode, you will still have kitchen extract for the MVHR.

11 hours ago, CJER said:

The concern with a recirculating was it just isnt as efficient removing grease/moisture as a recirculating

Don't be concerned, I rarely even use our cooker hood - MVHR does the job 99.5% of the time. 

 

Your issue isn't the cooker hood it's the fire.

11 hours ago, CJER said:

MVHR (Venti Fluxo)

What is a ventilation fluxo you refer too?

 

11 hours ago, CJER said:

HETAS supplier and fitter for the burner, they said they would fit it with its own air supply due to the room having an extractor of some sort (hob) anyway, not sure if this then makes the venti fluxo redundant and unnecessary?

The air supply to stove is through wall so takes outside air to use as primary and secondary for combustion. It ensures stove doesn't use room air for combustion. It doesn't remove any need for room ventilation.