Bathroom fan - inline fan fitted outside on external wall in a sealed box

[Muppetatwork]

Hi there, I have a small downstairs bathroom, just over 6' x 6' x 9' and all the walls are tiled. The existing fan is a cheap Manrose Gold in external wall diagonally opposite to the shower. Anytime the kids take a shower the water is literally running down the walls. Also the fan tube goes to the corner of a large airbrick on the outside wall. Doesn't go through it, just rests against it so I guess a fair bit of the moist air is just going into the cavity.

Wondering if it's possible/ok to put an inline fan (Manrose MF100T) in a box on the outside of the external wall and run the ducting back up and into the hole where the existing fan is?
The benefits would be:
Minimal mess in the bathroom and easy to carry out work.
Channeling the ducting through the airbrick in a pipe stops moist air ending up in the cavity.
The fan noise would be outside so nice and quiet.
Easy to access for maintenance.

The existing isolator is postioned about 6 inches from the fan and would be easy to replace and run the cable - is it ok to do this regs/rules?.
Regards sitting the fan in a box (I would waterproof the box) - does it need ventilation to stop overheating, e.g, grill on the underside, a lot of airspace in the box?

The instal instructions only show it being posititioned horizontally - wonder if its ok to fit vertically to avoid any condensation issues?

Thanks in advance

 

[ericmark]

My first action, would be to try only turning on the fan after they have finished in the shower. We really do not want to drag the water vapour out of the shower cubical.

Rules wise it is silly, it does not really say a fan must be used, it just says it must be there to use, so a simply pneumatic timer you press as leaving the shower is enough.

 

[Muppetatwork]

Thanks @ericmark Should clarify that its just a showerhead above the bath (no cubicle) and when they come out the bathroom water is properly running down the walls, dripping from the ceiling, blowing all wooodwork. Just replaced the cabinet under the sink for a couple of hundred quid and its starting to blow already.

For what its worth, I'm kind of thinking the the only difference between having an inline fan in a loft or outside as I'm planning is the volume of space that surrounds the fan.

 

[EFLImpudence]

when they come out the bathroom water is properly running down the walls, dripping from the ceiling, blowing all wooodwork. Just replaced the cabinet under the sink for a couple of hundred quid and its starting to blow already.

It sounds like you have more fundamental problems with very cold walls which needs heating.

 

[Muppetatwork]

It's fine when I have a shower. 5 mins in and out and you'd never know I'd been in

 

[Muppetatwork]

It sounds like you have more fundamental problems with very cold walls which needs heating.

Its at the corner of the building so two walls are exposed to the elements. Unfortunately, got to live with that.

 

[Murdochcat]

How is the bathroom heated?

Pushing steamy air into the cavity is dumb

Do you have enough airflow under the door ?

 

[JohnW2]

We really do not want to drag the water vapour out of the shower cubical.

Rules wise it is silly, it does not really say a fan must be used, it just says it must be there to use, ..

Which 'rule' requires it 'to be there to use?' Since this room has two outside walls, it seems quite probable that it has at least one window.

... and, of course, it's the same as you describe with windows - even if there is one, no-one can be forced to ever open iut (

 

[JohnW2]

It sounds like you have more fundamental problems with very cold walls which needs heating.

Quite so. If the walls are cold, then no fan will do a lot of good, because a fair bit of the humid air will condense on the walls before it gets to the location of the fan inlet!

 

[Muppetatwork]

How is the bathroom heated?

Pushing steamy air into the cavity is dumb

Do you have enough airflow under the door ?

It's got underfloor heating on a timer
The current fan exiting into the cavity is very dumb - even if I stuck with the current fan I'd need to get that sorted
Gap under the door is about 2.5mm
Its got a window too
I had been think of putting the inline into the ceiling void - it would fit but be tight and involve a plastering job but the real problem is there's some heavy metalwork (carport) and heavy power cables running round the outside of the house exactly where the fan would break out.
I think the existing fan clears 80m3/ph and the inline 240m3/ph
In the evening its not unusual for the shower to be on for good hour and a half

 

[JohnW2]

It's got underfloor heating on a timer

If that's the only heating, then the walls are presumably pretty cold - so, as EFLI and I have both said, you're probably going to have condensation running down those (cold) walls regardless of any fan. It's pretty basic physics

Although UFH in bathrooms seems fashionable (people like warm feet?) , it's probably about the last place where one really should have UFH as the only heating

 

[thomp1983]

2.5mm gap under the door is no where near enough, the fan has to be able to suck air into the room at the same time as dispelling air from it.

 

[flameport]

does it need ventilation to stop overheating, e.g, grill on the underside, a lot of airspace in the box?

No space required, the motor is cooled by the air flowing through the fan.
If the gap under the door is the only way air can enter the room then at least a 10mm gap is required, which for a standard door is approximately the same area as a 100mm diameter round duct.


However the real problem is this:

In the evening its not unusual for the shower to be on for good hour and a half

which won't be solved by any fan.

 

[Muppetatwork]

The gap under the door about 1cm on the bathroom side (can stick my fingers under it) but on the hall side the floor was raised and the gap is minimal. Slightly ironic, the hall floor was replaced because the bathroom had a slow leak which had seeped under the floor.

I'll cut a vent into the door and try relocating the fan to the other side of the room away from the air brick. I'm stuck with cold walls for the time being but long term I'm hoping we can extend out and insulate the walls. The kids will eventually move out to escape my complaining.

Thanks all

 

[ebee]

Limit the use of the shower to sensible times. ten mins should be more than enough for a reasonable shower time in most instances (it used to be common to quote shower time as 6 mins) so whether electric heated shower or run off a boiler then the shower time you mentioned is quite exceptional.
Limiting it to 10 mins max in most normal circumstances could reduce your wet walls quite a bit. So too could limiting next shower usage to at least 30 mins after the last usage might help too.
Of course for medical conditions and if you are a family of three adults and ten children it might be a bit difficult to achieve these time limits but it all helps cut down your potential problem.