Long kitchen extractor duct. Supplementary fan?

[shadrack]

I am installing a standard cooker hood type extractor. For various reasons, the ducting will have to follow a long, tortuous route of about 18 feet with possibly 5 right angle bends. I assume that there will be a loss of power because of this.

Would fitting an extra in-line duct fan at the outlet help? Does anyone have experience of this?

 

[breezer]

bends will obviously reduce flow considerably, i have two fans on my bathoom ducting, works very well, but i suggest your 2nd fan should be the same as the first

 

[shadrack]

Many thanks for that Breezer. It's unlikely that I'll be able to match the in-line duct fan's specs with the cooker hood's. How important is it that they are matched?

 

[breezer]

i wouldsay very, because if one if faster than the other you will / may have problems

fan a blows at 50l hr
fan b blowsat 40l hr

a is first fan b is 2nd fan

where do the other 10l go? try it i may be wrong

 

[AJP]

Fitting hood myself, it recommends 3M max hose, -1m for every bend at 90 degrees.

Do the instructions rate the fan in your hood for max length + bends etc?
These fans SUCK not blow, so you need to fit matching fans or one will out perform the other, 10 l per minute is a lot. It's the same vol as 20 cans of 500ml beer per minute!! will introduce a leak if your system is airtight at installation.

 

[breezer]

the figures i used were used to demonstrate a point the actual difference may bemore, it may be less.

as for "These fans SUCK not blow" that depends on which side of the fan you are on doesn't it

 

[shadrack]

Many thanks for the advice. Sounds as though I should try to avoid the use of a second fan if possible.

My extractor fan instructions say 4m max with "as few bends as possible", and recommends 5" ducting. If I make most of the run 6", then I'm cutting the resistance down as much as possible so hopefully I'll get away with it.

Thanks again.

 

[ill_wind]

If you have room run two ducts this will reduce the back pressure on the fan.