Query re. mounting mixed flow fan in loft

[matei]

Hi all,

I'm in the process of having my bathroom redone, and one of the things I want to do is replace the fan in the droplight/fan combo with a more powerful mixed flow fan mounted in the loft, keeping the actual light unit (just put the new fan downstream in the loft).

The current fan is next to useless, it just makes noise and has no real suction. The way it was set up is that the ducting runs into the loft and then outside, but the exhaust is about 30cm above the loft floor, along which the ducting runs.

I had read that some mixed flow fans will gather condensation inside if there is too steep of an angle to the exhaust opening. In that situation, how does one mount the fan?

Here is a pic (we had just moved in, there was some rubbish in the loft from the previous owner), the white duct comes from the shower cubicle and then is connected to the outside wall.

Any info would be appreciated - thanks!

 

[stem]

Some, if not all, mixed flow fans can be mounted in horizontal or vertical orientations. So, you could mount the fan on the wall as close to the outlet as possible whilst maintaining a decent radius of the duct where it passes through the wall.

Regardless of the type of fan, condensation can form on the inside of the duct, which in an unheated loft in winter, will present a cold surface to the warm moist air inside it. Where the duct is exposed, wrapping the duct in pipe insulation will help. After that, if you do find condensation to be a problem, which I doubt, a condensate trap can be fitted later at the bottom of the vertical section. This collects any condensation and allows it to be drained away.

Untitled

• stem
• 25 Feb 2013

 

[matei]

Super - thanks for the advice, appreciate it.

 

[matei]

Aha - seems that the previous owner already has some sort of mixed flow or centrifugal fan there... up until now I hadn't been able to look at it up close.

Is there any particular thickness or spec lagging that is recommended?

I was considering mounting the fan directly on the wall, to the left of the outlet, slightly higher - with the output of the fan tilting down towards the outlet, let's say at ''11:00 high", for lack of a better description I would of course wrap the duct in insulation - the last thing I want are condensation issues in the loft. I had that in a previous property and it resulted in lots of mould/mildew damage.

Does that sound like a workable solution?

thanks again for the help!

 

[Taylortwocities]

For your own energy consumption, the thicker the insulation is in the loft, the better!

It doesn't matter where you mount the fan, you'll still have the issue of warm moist air in the duct meeting cold air in the loft. And that will create condensation INSIDE the duct..
All you need to do is to find a way to drain the condensation - using one of the traps that STEM has posted.

If you want to avoid condensation in the loft, then you need to pay attention to the downlights (I spy one in your picture).

This needs to meet Building Regulations Part C requirements. To keep your heat in the house you need to fit
a loft cap

or loft brace

and cover over with insulation - otherwise warm, moist air will be drawn into the loft by the downlight.

 

[matei]

Yes - thanks for that, good observation. I don't know why the insulation was lifted up there. None of the other spots have caps, but they're just covered by insulation

 

[endecotp]

I was considering mounting the fan directly on the wall, to the left of the outlet, slightly higher - with the output of the fan tilting down towards the outlet, let's say at ''11:00 high", for lack of a better description!

An alternative would be to fit it to the rafters. You might manage to get a vertical length of rigid duct from the ceiling up to the fan. Then re-use some of the existing flexible duct from the fan to the wall.

Or build/bodge something to fix the fan so that it is horizontal and aligned with the hole in the wall: pipe comes vertically up through the ceiling, 90 degree bend into fan, then horizontally straight out through the wall.

It's possible to buy insulated flexible duct. Wrappig mineral wool around your existing flexible duct should be possible, with some care. The advantage of rigid duct is that it's easier to be sure that there are no sags where condensation can pool. It's also easy to insulate as it doesn't crush.

 

[Steve]

My number one priority would be to chuck some insulation at that loft! I've got nearly a foot of insulation in my loft.