Cooker Extractor for a 3.5 Metre Duct length

[bernardgreen]

I like your thinking! Very heavy weight, but if you can collect it may be cheaper

Plastic so about 8 Kg

Or

http://www.polypipe.com/housing/abo.../polypipe-soil-160mm-3m-plain-ended-pipe-grey

Gross Weight Kg: 7.095

 

[Jupiter01]

Would this not create problems for when I connect fittings to this e.g. grill, bends. Wont they be at the 150mm size?
Also, I' concerned that this will be very heavy especially if it is resting on the plasterboard ceiling. Remember that I wont have an opportunity to clip it to the joists as I am pushing it through one end of the wall.

 

[John D v2.0]

You might need some ingenuity to get it to fit.
The ready made ones are far lighter and you don't need much surgery to attach them.
My only concern is the cost of delivery, last time I ordered a load of ducting it arrived on a pallet, I think I had to spend 150 to get free delivery.

 

[Taylortwocities]

What a co-incidence. I just had a delivery from TLC of two lengths of their 150mm plastic duct.
Decent quality and not too heavy either.
They have a good selection of accessories to go with it. too.

 

[Jupiter01]

OK. Based on all of the advice, here is my plan: I will remove the external grill and I am hoping that this will allow me to see the current flexible duct and allow me to get a gauge on impediments that may affect the pushing through of a new round 150mm duct. I will then place a draw cord and remove the existing duct and push through the new one.

If upon closer inspection, I can see that getting a round 150mm duct will be difficult, should I opt for a square duct instead? Are there any limitations.

Sorry for the incessant questions but I want to make sure I get this right after all of the upheaval that it will be causing.

 

[John D v2.0]

Sounds good, a rectangular duct has the same area but greater surface area so more resistance.
Also the fitting aren't as flexible - with round you can angle it how you want but rectangular the fitting only fits two ways. And it can sag very slightly due to being a slightly less rigid structure.
Hope it goes well!

 

[Jupiter01]

Update - I removed the external grill this weekend with the intention to see what lurks within. You may recall that the duct run is around 3 metres and i assumed that I would be able to look through and see this run to assess whether there are any obstacles.

FAIL - The flexible duct curves and as a consequence, I can only see around 30cm of it. I fear that if I pull it out, I have no assessment on whether I can get the 150mm duct in its place and ultimately, I will need to cut the ceiling to get it in. My ceiling was only boarded and plastered 3 months ago.

I wonder if I could get away by leaving the current 100mm duct in place but upgrading my hood. My current hood has an extraction rate of 338m3/h and I've seen one online that has an extraction rate of 690. Should I try this at the first instance?

 

[ban-all-sheds]

My ceiling was only boarded and plastered 3 months ago.

Something must have blocked the duct then, or it got damaged when that work was done. If it was all working fine 3 months ago, something sudden must have happened.

 

[Jupiter01]

I think the current duct is intact as I can feel a reasonable amount of air when the extractor is switched on. My issue was the lack of efficiency and I wonder if that can be helped by replacing the hood with one which has a much higher extraction rate.

 

[John D v2.0]

Not really, trying to force more air through a bendy small pipe is most likely to just cause more noise and pressure.
You can try to calculate the air velocity at that extraction rate through that duct, and the mass of air hitting the flexible sides of the duct each second. It could get noisy.
By all means try, but I don't think you're on to a winner.

 

[ban-all-sheds]

I think the current duct is intact as I can feel a reasonable amount of air when the extractor is switched on. My issue was the lack of efficiency and I wonder if that can be helped by replacing the hood with one which has a much higher extraction rate.

Well what happened in the last 3 months to reduce the efficiency?

 

[EFLImpudence]

Are cooker hoods designed for whole room ventilation?

 

[ban-all-sheds]

Only for infeasibly small rooms.

 

[ban-all-sheds]

☼

 

[Jupiter01]

My current hood blew its motor. As I said the extraction rate on this is low, whereas the new motor has twice the extraction rate. I am hoping that this may save me from having to cut open my new ceiling.