Shower Extraction through loft space

peacey2102 · 6 Jan 2007

I have installed an in-line extractor fan from my shower enclosure, into the loft space and horizontally out through a gable wall.

The run is quite long (about 7m).

The problem is, I had to use flexible ducting on the stretch upstream of the fan (noise was too high with rigid soil pipe bend on ceiling spigot). Now I am getting a lot of condensation in the flexible section, causing it to sag.

It's difficult to find the right rigid/flexible combination to get the necessary low noise and yet get drainage correct. I know that condensation traps are available, but will they work in a horizontal run. I know I need to insulate the duct, but will this eliminate condensation completely, in an un-heated loft space? Can I just lay glass fibre blanket over the pipe, or do I need to lag it with proper pipe insulation.

Any advice would be greatley appreciated.

JohnD · 6 Jan 2007

You can flop loft insulation over it, but for such a long run, get a roll of the stuff with a plastic wrapping round it, bandage the pipe in that and tie it on securely (you can use sticky tape, but it tends to tear the plastic wrap as it pulls).

Consider using plastic soil pipe instead of flexible hose, it will allow water to run down a slope instead of being trapped in the convolutions, so you can give a slight fall to the exit.

You have quite a long run and may benfit from a more powerful extractor than usual, preferably a Centrifugal fan. When you stand outside on a cold day, do you see the steam gushing out vigorously?

I don't understand why the rigid was noisy.

Deluks · 6 Jan 2007

JohnD said:
I don't understand why the rigid was noisy.

Cos it's rigid. The flexible pipe will absorb vibrations from the fan.

JohnD · 6 Jan 2007

so clamp the rigid, and use a short flexy link for the bend at the fan.

Deluks · 6 Jan 2007

JohnD said:
so clamp the rigid, and use a short flexy link for the bend at the fan.

Sorted

I know of a guy who used a pair of his missus leather trousers to make 'silent' ducting, in an mdf fan enclosure.

peacey2102 · 6 Jan 2007

Thanks for your many replies.

I'd toyed with many different solutions before getting to the set up I have now. I am using soil pipe for the rigid bits already. Trouble is, flexible doesn't fit over soil pipe. That's why I ran flexi all the way back to the fan (which by the way is a Soler & Palau TD 160 TD Mixed flow fan from TLC Direct). More than meaty enough for the job.

I think I'm going to reposition the fan right to the start of the run and just have the flexi for the bend into it from the ceiling. Means extending wiring, but that's the least hassle to get the required noise levels and fall on the duct. I can then use the soil pipe with a continuous fall from the fan to the outlet.

One thing has amazed me - just how much moisture is extracted and has condensed inside the duct.

Nay ideas as to what to mount the fan on to reduce vibration transmission through the trusses? At the moment, it's just sat on an old piece of folded carpet on top of the fibreglass.

Deluks · 6 Jan 2007

peacey2102 said:
Any ideas as to what to mount the fan on to reduce vibration transmission through the trusses? At the moment, it's just sat on an old piece of folded carpet on top of the fibreglass.

mount it inside an mdf box (with lid) then make a bigger mdf box (with lid) 6" wider,taller,and deeper than the first one. Line the bigger box with 3" thick rockwool type insulation on all 6 sides, and put the smaller box inside.

Of course you'll have to cut holes in the boxes and rockwool at each end of the fan. Fix flexi ducting to the outside of the bigger box, but don't fit any ducting on the inside. So the air flows across the 3" rockwool filled gap on both sides of the fan. This will absorb some of the fan noise.

^woody^ · 6 Jan 2007

Much of the noise from loft fans is due to vibration through the fixing, and not sound through the air. But a cheap chinese one is going to be noisy whatever

The fan (and duct) should be isolated with dampening material wherever it connects to the structure - especially roof or ceiling timbers

peacey2102 · 6 Jan 2007

To be honest, the noise is really not bad at all, as long as the fan is isolated from the roof timbers. It certainly doesn't warrant an acoustic enclosure. To be honest, the installation is much quieter than the crappy ceiling mount fan that the builders had fitted. I just have to make sure the fan doesn't contact the roof structure. The fan itself is a very quiet unit.

I think I'll just experiment with some different densities of foam or insulation to stand the fan on.

Deluks · 7 Jan 2007

Get creative and make a shockmount out of old bicycle inner tube or other rubber strip type stuff.

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Shower Extraction through loft space

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