Downdraft Extractor Ducting Route

[carson321]

I wasn't sure whether to put this here or in the insulation&ventilation forum.

 

I want to have a venting hob with a downdraft extractor installed in my new kitchen island. It is going to be situated over a block and beam floor in our new extension. Should I be directing the duct through the floor makeup above the block and beam (200mm insulation, 65mm screed, about 2.4m horizontal run to external wall) or can i take it directly through the block and beam floor to the void under this? And if I do go in to the void, could I just have it terminated here as it will have passive ventilation installed anyway, or should I direct it the whole way out through the wall?

 

Appreciate any insight on this. 

[Wil]

Are you having MVHR? Best to have the downdraft re-circulate into the island via carbon filters and do your air removal through the nice efficient MVHR if a new extension.

 

definitely don’t want kitchen grease building up in a void under the floor. Where does the air go if you shove it into the void?

 

If you do duct to outside put a good non-return flap on it- Our friends have a permanent towel over their hob when not in use.

[mistake_not]

Before I decided to install MVHR I was going to go outside and use a Naber Compair tower as an outlet. Had all the baffles and nice things to not leech heat. In fact I got as far as buying one that's still sat in my garage....

 

https://forum.buildhub.org.uk/topic/42930-naber-compair-tower/#comment-604747

[carson321]

No MVHR, so looking for venting as will negate the need for a background extractor in the kitchen. The floor void will have plenty of its own ventilation per building regs and I don't know if I would need to be bothered about any grease per se, as its just a void with a load of clay soil under it! 

[Gus Potter]

10 hours ago, carson321 said:

Appreciate any insight on this. 

Avoid, it's a gimmic!

[saveasteading]

Absolutely not venting into the void.

 

Condensation and damp will be caused.

Your void should be  vented but not enough for this purpose.

There is a risk of grease and other foodstuff buildup too,  if the filters fail.

 

The hob extractor is for the cook's visual benefit and comfort,  and heats the cook's feet and  the room rather than wasting it.

 

I assume the filters are efficient and take out the smells.

 

Ventilation of the room must  then be by fan to outside.. heat recovered or thrown away is your decision.

So in your case just a simple fan with a switch.

 

I've looked at these hobs. The duct seems to be quite small and convoluted through the kitchen unit,  so the fan will only be powerful enough to vent at the skirting as designed, not through additional ducting.

[Nick Laslett]

I wonder what wild life a steady supply of cooking grease would create in a warmish, sheltered vented space like this?

 

You could develop quite an ecosystem after a few years. 
 

Makes me think of the warm water outflows at a Nuclear power station, and how it attracts massive amounts of marine life. 
 

Perhaps it is a situation to try and avoid.

[saveasteading]

34 minutes ago, Nick Laslett said:

warm water outflows at a Nuclear power station, 

 

Tuna swimming around the undercroft?

 

[carson321]

Im not suggesting that I am going to or think it is a good idea to vent in to the void, was just canvassing for opinions/ info on the subject. 

 

These vents are more than capable of extracting through ductwork externally and not just recirculating through the base boards.

 

I was considering just using one in recirculating mode, but now that I know my floor makeup is going to include 200mm insulation, I am considering an external vent as I like the thought of not having an ugly background extractor randomly stuck on one of my walls. 

 

[saveasteading]

2 hours ago, carson321 said:

These vents are more than capable of extracting through ductwork externally 

I'm surprised. Are they designed as such? 

[carson321]

37 minutes ago, saveasteading said:

I'm surprised. Are they designed as such? 

 

Well BSH group give instructions on how to do it and details maximum ducting runs etc.

[JohnMo]

For me I would 

Do in recirculated mode and come out at the kickboards below your kitchen units. Then install a dMEV (with automated humidity control) fan in kitchen plus all other wetrooms. Undercut all internal doors and have humidity activated trickle vents on all dry room windows or through their walls.

 

Have a proper ventilation strategy.