Which extractor fan for long duct run?

[HappyHippyDad]

The customer has a bulk standard axial fan located in the ceiling of a small shower room (approx 2mx1m). The shower room has no door, just an L shape into shower from bedroom.

The ducting goes through the loft at a run of approx 5 meters. It pretty much starts off vertical for around 1 meter and the ducting continues along the ceiling of the loft and eventually out through the eaves.

The chap says he has lots of condensation coming into the fan and it now stays on continuously even with the light off.

I dont like the long vertical run as it just asks for condensation to fall back into the unit so would be locating ducting along floor of loft. My question is which fan for the long run? An in-line fan probably but I am unsure of what m[SUP]3[/SUP] p/hr is required. Also m[SUP]3[/SUP]p/hr seems to be dependant on the area of the shower rather than length of ducting? Is a higher m[SUP]3[/SUP]p/hr going to be better for a long ducting length or should I be looking at a different form of fan (centrifugal??)?

Thanks all..

 

[GLENNSPARK]

in line centrifugal fan.....

http://www.google.co.uk/#q=inline+centrifugal+fan

 

[MDJ]

To add you may find using double insulated flexy duct helps with condensation.

 

[Marvo]

Measure the volume of the L-shaped shower room and find a fan that can move 15-20 times that volume per hour on the centre of its performance curve. Don't use the 'free-air' figure that the manufacturers love to state on the box because you'll come short, look at the performance graph and avoid any fan that doesn't come with one.

As already suggested a forward curve centrif would be best, it can handle higher static pressures associated with long duct runs and look into using a condensation trap as well.

 

[Octopus]

Try this for starters:

Suitable Fans

 

[soulman]

You will need a mixed flow inline fan. Manrose do a good one for around £70.00. Dont use flexi ducting use rigid. The size of fan is determined by calculation of the room size & how many air changes is required etc.

 

[SPARTYKUS]

Solid (eg soil pipe or similar) is better than flexi on long runs, flexi can have little pools of moisture and create monsters waiting to excape.

Also a good tip is to wrap insulation around the entire run (space blankets are good) to help stop the moist air consensating.

its a minefield. And I have learnt a few lessons the hard way.....

 

[MDJ]

I mentioned double insulating Duct, The reason, we have found it stops moisture due to the fibre glass in between the double insulation. Never had a problem since we started using it to be fair.

 

[robsparky1975]

Envirovent,fitted a silent 4" in bathroom a few weeks back,might be worth a look.

 

[JulianC]

A 4" centrifugal fan will do the job nicely. You require a minimum extract rate of 15l/s (54m[SUP]3[/SUP]/h) for an intermittent extractor. As a rule of thumb, at this extract rate you can use up to 6m of ducting and no more than 2 bends (bend radius no less than duct diameter) before the fan's rice pudding skin pulling ability is compromised. If using an inline fan, check manufacturer's requirements for ducting. Rigid ducting where possible is best. If using flexi, pull it tight so it is extended to at least 90% it's full length and provide regular support so it doesn't sag. Ducting should be insulated in the unheated loft, either by use of insulated ducting, or lobbing rockwool over standard ducting. If using vertical runs, fit a condensation trap. Nuaire's Genie range are top notch, but pretty expensive.

 

[HappyHippyDad]

Thanks alot guys,

In-line centrifugal fan it is. Customer does not want to spend more on specific insulated ducting so have strongly advised to at least cover with insulation. I would have liked to have insulated it myself to make sure it is done but he says he will do it himself! I feel responsible seeing as though I am fitting the fan (legionnaires disease etc etc) but I cant force him to let me do it and I have made it very clear how important it is to insulate!