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?

 

[jj4091]

Any condensation will evaporate. Especially with underfloor heating. Personnely I would take it on the surface, not in the cavity, above the DPC as you probably won't know at this stage what your outside ground level will be. Use flat ducting.

 

[CJER]

Any condensation will evaporate. Especially with underfloor heating. Personnely I would take it on the surface, not in the cavity, above the DPC as you probably won't know at this stage what your outside ground level will be. Use flat ducting.

Thanks for your advice, when you say surface, is that as in above insulation or do you mean the surface of the wall?