Bathroom extractor fans

[footprints]

I am looking at replacing my bathroom extraction fan, because of the roof line the existing one goes out of the side wall only 120cm from the floor, even left on for an hour it still does not stop condensation.

Short of going directly up through the roof which I don't want to do, as it will tend to work as a flue causing a draft and I really do not want to compromise the roof its self. In addition because of the roof shape decending so low it is a very long way up the roof If I ever need to repair.

The only solution seems to be a loft fitted fan then ducted down internally to exit at the present level.
Trouble is the only practical way to duct down means using 1.5m of 100mm flat trunking and 3 flat bends in addition to a short length of round duct from the vent to the flat via the fan.
An awful amount of resistance! any suggestions on what power of fan I need please?

 

[ericmark]

Three houses, two no problem with growth of mould, one massive problem, so I looked to see what was different, and realised it was the barriers around the shower, two with no problem, one no barriers a wet room, the other sealed at the bottom, one with problem was in a bath so there was a chimney effect, and the moisture was circulated around the bathroom.

It is not as simple as just the extractor, in fact the wrong placement can make it worst, and draw moisture into the room, also where does the replacement air come from? Drawing air from a cold hall and likely that air is reasonably dry to start with, my house is around to 50% humidity, the house with a problem was more like 75% humidity, if the replacement air is not dry to start with, then no fan will help.

 

[Murdochcat]

When you say the existing fan isn't effective, have you checked there is sufficient airflow under the door to allow the fan to draw dry air into the room?

I mention this because this is often the primary reason for a fan appearing to not be good enough

And don't have the window open either

And how is the room heated?

 

[SUNRAY]

When you say the existing fan isn't effective, have you checked there is sufficient airflow under the door to allow the fan to draw dry air into the room?

I mention this because this is often the primary reason for a fan appearing to not be good enough

I have to agree with this, on of the places I worked had their compressor in a shipping container behind the building, by the switch is a sign saying open the container door before starting. One day it wasn't opened, after a short while the air pressure dropped off. and the overload tripped. we tried opening the door but an hour later still no luck.
Someone decided to drill a hole in one side and when the drill broke through (maybe 3mm) it snapped and the broken piece flew across to hit the other side. the whistle of air rushing in was loud and hardly quietened when enlarged to 12mm.
It was still whistling until the door was pried open many minutes later.

 

[JohnD]

Builders commonly fit a cheap 100mm fan with a nominal throughout of about 80 cu.m/hr.

I use these and consider that if turned on every time the bathroom or WC is used, with a 20 minute timed overrun, they are adequate, but nowhere near enough if you have steamy showers or the room is poorly insulated and the walls prone to condensation.

For a room with shower, I usually recommend a 240 cu.m/hr fan, with timed overrun. There are some good ducted inline fans, that are inaudible when correctly fitted above a ceiling

4"/100mm In-Line Duct Extractor Fan - 250m3/hr c/w Timer | Soler_&_Palau (5211364500)

You can mount in the loft if you have access, or conceal in a cupboard, but if you need a wall fan it will need to be a large one. Have you got an airbrick?

This 150mm fan will do it, and is a good make with a quiet ball-bearing motor and a backdraught butterfly

Silent 300 CRZ 6"/150mm Extractor Fan c/w Timer - White | Soler_&_Palau (5210418900)

You will need a gap under the door so fresh air can enter and stratify beneath the water vapour (which is lighter than air so rises to the ceiling).

 

[footprints]

Thank you all for your replies and suggestions.
To try and cover them all.
The loft is insulated, the walls are cavity no insulation other than thermal paper.
The rad is pretty big see photo.
There is a finger sized gap under the door, which is left open after showering with the fan running for about an hour.
The adjoining room is the home office.
Shower is over the bath and has a curtain not enclosure.
You can see from the photos it would be hard to pick a worse place for the fan apart from the skirting board!

 

[JohnD]

Leave the door shut when running the fan, as well as the window. This creates suction that prevents water vapour diffusing through the house, and also enables the still air in the bathroom to stratify, with dry, cooler air lying beneath the warm air and watervapour, which is lighter and rises and will be drawn out.

This is also why putting the extraction vent as high as possible will improve removal of steam.

Do you have scope to put it in the ceiling? Can you run a duct in the roof ridge to emerge from the gable?

Incidentally, all the time water is evaporating in the bathroom as it dries, it creates a vast volume of water vapour, which reduces the amount of cool air drawn in under the door.

 

[footprints]

Yes JohnD, the plan is to put the ceiling vent over the shower end of the bath, run 4" flex to the unit and and duct down between ceiling and roof into the gutter and soffit hence the need to use flat duct, or failing that run the duct in the bathroom with an enclosure, but that's gonna look pants!

 

[JohnD]

If you can find a good roofer, you could have ridge tile or vent tile, and rely on the backdraught shutter to prevent unwanted airflow. I am generally not in favour of holes in roofs unless constructed by a skilled roofer.

 

[footprints]

If you can find a good roofer, you could have ridge tile or vent tile, and rely on the backdraught shutter to prevent unwanted airflow. I am generally not in favour of holes in roofs unless constructed by a skilled roofer.

Might come to that, trouble is the only good firm I would recommend just told my neighbour they can't call to quote for 3 months! Chances are they will want scaffolding too!

 

[footprints]

Update if anyone interested.
Went with a Manrose MF100T.
Old vent on wall now redundant.
Spent the best part of a day wheedling the flat duct through the pitched roof and through the soffit, but working fine now!

 

[footprints]

PS I know in the picture it looks like in runs down both ends but it does drain to outside just my bad photography I guess!

 

[JohnD]

It is best to wrap the duct in insulation to combat condensation.

Some ducts are sold ready-insulated.

 

[footprints]

It is best to wrap the duct in insulation to combat condensation.

Some ducts are sold ready-insulated.

Yes I have finished the insulating today, now all snug!