Bathroom ventilation fan

I'm getting black mould in my bathroom, and I expect it's because there is no ventilation fan in there to extract damp air after the shower has been used. I can leave the window open for a bit, but that goes out to an enclosed porch and isn't great in winter. So it seems that I need to install a ventilation fan.

The most convenient place to fit it is at the back of the bathroom, but the air-brick that vents through to the attached garage (the two share a wall) is also at the back. Will it make any difference to the effectiveness of the fan if the route for bringing in the replacement air is effectively just below the fan itself? Some will come in around the door, of course, but that's pretty much at the back too. 

In my head I'm thinking that it would be better to have the fan at the opposite end of the room to the air-brick, but will it really matter? It's much more inconvenient to put it at the front, as I'd like to avoid having a vent visible on the front of the house.
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Comments

  • A bit more info on this layout, please.
    You already have an air brick in that bathroom, but it heads out into your garage? At what height is this brick? And could it be routed from the garage to the outside via some ducting?
    In general, as you say, it's best to have the extraction (a) as close to the steam-producing source as possible, and (b) at the opposite end of the room to where the replacement air comes in. And I would suggest that the replacement air is from the house, as it'll be warmer, so will help to dry out the bathroom.
    Could you make a simple plan showing the bathroom, the garage, the outside - stuff like that?

    Best case scenario is if this air brick is high on the wall, so you could remove that and turn it into a ducted grill, and fit an in-line extractor fan out in the garage where it would be quieter, and then exhaust that outside the garage.
  • Andreg
    Andreg Posts: 183
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    edited 19 December 2023 at 10:43AM
    Are you saying there's an air-brick in your bathroom wall that brings air from the garage into the bathroom!?  Where exactly is the air brick in the bathroom?  I would not put an extractor between a bathroom and a garage, but an extractor that removes air from the bathroom directly to the outside should be fine.

    You say the air-brick would be 'just below the fan'.  How far below exactly?  If its more than a few feet then the air going into the air-brick is not likely to be significantly contaminated by the extracted air.

    Until you get the condensation fixed I recommend you wash down the mouldy walls with bleach or mould remover regularly to prevent its spread to other locations.
  • It’s often possible for extractor fans to be vented through the bathroom ceiling and along the roof space to a better outside wall. 

    would've . . . could've . . . should've . . .


    A.A.A.S. (Associate of the Acronym Abolition Society)

    There's definitely no 'a' in 'definitely'.
  • droopsnoot
    droopsnoot Posts: 1,734
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    Hi, thanks for the responses. This is the approximate bathroom layout, not to scale:




    The window opens into the porch, which is UPVC double-glazed. At the moment I have a window slightly open, but am trying to balance ventilation and heat.

    The airbrick is denoted by the green line, on the wall near the toilet at the top of the diagram. It is approximately 12" from the floor, possibly the worst place to ventilate warm air, though when the house was built (and the air brick installed) the porch wasn't enclosed, it was just a canopy. On the other side of the air brick is an attached brick garage, which has been part of the house since it was built.

    Going in some sort of order:

    I could probably duct from the air brick to the outside of the garage, though it would be quite intrusive - I've have to duct upwards so that the outlet was above the back door of the garage as there's almost no room between the door (personnel door) and the join to the house. Should have put that on the diagram, really. I wouldn't want to do it this way, really. I can block the air brick without any trouble once I have the ventilation sorted, if it's better for the replacement air to be coming from inside the house.

    This is a front view of the layout of the house / bathroom:



    In the lower section of the roof that you see above the join between the bathroom and garage, there is a triangular space (side loft) that I use for storage. The access door is towards the back of the bathroom and the room above it. That makes it easier to get in and access above the bathroom ceiling to install the fan and ducting, and to access it for maintenance, if I fit it at the back end. The garage roof also drops away towards the rear, so the height of the section I've captioned "boxed in here" is higher at the back than at the front. I therefore have a bit more space to get the ducting out of the loft, into the boxed in area and out of a vent at the back of the garage.

    The easiest route would be to put a fan in the side loft at the front of the house, and drill out through the front wall above the bathroom for the outlet vent. I don't really want to do that for two reasons - first because the side loft has a load of stuff in it that will make it a pain to access for maintenance purposes, and second because I don't really want a grille visible on the front of the house. If I go out sideways, I have to try to feed the ducting down through the eaves (covered in a grille) and then out through the boxed-in section. I'd like to not disturb the boxing-in because it stops "stuff" gathering under the eaves and holding damp. That's why I'd prefer to do it at the other end if it'll still work.

    I have just been and given it a wipe over with some flash in hot water and it's got rid of a bit of the black, but not completely. I'll give it a day or two and then go over with some bleach instead. It's really tricky to get to the part that's badly affected, because it's a poor bathroom layout - the gap between the front of the shower cubicle and the front wall is about 12", so I can't get anything in there to get high enough to reach the corner. I'll have to make a custom "thing" to stand on as I also can't put the steps in the shower cubicle itself.
  • grumbler
    grumbler Posts: 58,629
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    Instead of venting into the garage, I think it's better to make a  duct through the garage to an outside wall roof. And you can have a more powerful inline fan installed in the garage.
  • droopsnoot
    droopsnoot Posts: 1,734
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    edited 19 December 2023 at 1:25PM
    Thanks, but I mustn't have explained it properly. I don't want to vent into the garage, or into the loft space of the house. I may have to go via the garage if there's no other way, but if I can put the vent in the ceiling I may just have enough room to bring it out above the garage roof but below the eaves (if that's the correct word for the bottom edge of the roof). The issue was whether it will be effective at the back end of the bathroom as that's the most convenient access for installation and later maintenance.

    While the diagrams above give an idea, I can't think of how to draw the back end arrangement of walls and roof to make it clear what I'm talking about.
  • ic
    ic Posts: 3,285
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    It looks like your roof is easily accessed from the roof of the garage.  What about a ceiling fan above the shower, venting out of the roof or soffit?  Whatever you get, make sure it has a humidistat so it keeps running until the room is cleared.
  • ThisIsWeird
    ThisIsWeird Posts: 4,458
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    Does the bathroom and the garage run side by side for most of their lengths? Ie, could you add your garage to the 'plan' view, the first one you've added?
    If so, the best way would be a near-ceiling height cut-through to the garage in the most suitable duct sizing - this could be as little as, say 4"x2" rigid ducting, which could then run attached to the garage ceiling, to a suitable place to fit the inline fan, and then outside. And the best place to cut through to fit this grill would be above the shower - extract the cause at source.
  • droopsnoot
    droopsnoot Posts: 1,734
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    edited 19 December 2023 at 7:04PM
    ic said:
    It looks like your roof is easily accessed from the roof of the garage.  What about a ceiling fan above the shower, venting out of the roof or soffit?  Whatever you get, make sure it has a humidistat so it keeps running until the room is cleared.
    It is easily accessed from the flat garage roof, and from the inside via the side loft. I have considered these vent tiles, though I'm not sure they're available in the right profile, but I'm really asking whether my plan to install the fan at the back end of the bathroom is going to be such a compromise that it won't be worth doing. Someone mentioned a humidistat, I had just been thinking of a fan with a run-on timer or maybe even just a fan that runs while the light is on.

    The problem with the soffit is that it is boxed in to the garage roof, so I'd have to be doing some sort of keyhole surgery to access the grille that runs under the soffit - the grille is in sections around 4' long, so I'd need to remove a section to cut a hole to run the ducting through, and then try to get it back in place. That would be easier at the back because of the downward slope of the garage roof meaning that there's more room to work there.

    Does the bathroom and the garage run side by side for most of their lengths? Ie, could you add your garage to the 'plan' view, the first one you've added?
    If so, the best way would be a near-ceiling height cut-through to the garage in the most suitable duct sizing - this could be as little as, say 4"x2" rigid ducting, which could then run attached to the garage ceiling, to a suitable place to fit the inline fan, and then outside. And the best place to cut through to fit this grill would be above the shower - extract the cause at source.
    The bathroom and garage do run side-by-side for the full length of the bathroom, and in fact the garage sticks out a few feet in front and forms the side wall of the porch. By the time we're at the back of the garage the roof has sloped down quite a distance, and it'd be at least 12-15" below ceiling height to get the fan to vent into the garage. If I run the ducting below the roof support beams in the back of the garage, it would be pretty low unless I do some sort of flattened ducting. I also have some water pipes around there - the boiler is in the garage, so I have flow and return to the hot water cylinder, and the same for the radiators. 

    I could install it at the front of the bathroom, but then I'm back to having a grille on the front of the house, which if you recall from my post is something that I'm trying to avoid if I can, or a complex job to make it escape via the soffits because there's less room to work.
  • ThisIsWeird
    ThisIsWeird Posts: 4,458
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    The bathroom and garage do run side-by-side for the full length of the bathroom, and in fact the garage sticks out a few feet in front and forms the side wall of the porch. By the time we're at the back of the garage the roof has sloped down quite a distance, and it'd be at least 12-15" below ceiling height to get the fan to vent into the garage. If I run the ducting below the roof support beams in the back of the garage, it would be pretty low unless I do some sort of flattened ducting. I also have some water pipes around there - the boiler is in the garage, so I have flow and return to the hot water cylinder, and the same for the radiators. 

    I could install it at the front of the bathroom, but then I'm back to having a grille on the front of the house, which if you recall from my post is something that I'm trying to avoid if I can, or a complex job to make it escape via the soffits because there's less room to work.

    We need some pics!
    You can do a lot with flat, rectangular ducting, like: https://www.screwfix.com/p/manrose-204-x-60mm-flat-channel-1m/59769
    So, you can try and work out how to run this in between the garage joists, or - if it must fit on them - it won't stick down by more than 2". The fan itself can certainly be mounted in between joists, so not stick down any further.

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