Condensation and dehumidifiers

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  • Condensation and dehumidifiers
  • Premier Icon sadexpunk
    Subscriber

    yep its that time of year again, we’re just in the process of redecorating our bedroom, pulled up the carpet and the underlay’s wet, with mould starting to accumulate on skirting behind drawers and under bed..
    had this problem a few years ago, with clothes going green in drawers under the bed, so got our builder to stick us a couple of airbricks in. To our dismay we found the airbricks were always wet and mould growing around them. id have thought that was the place where youd be least likely to find that!

    we also bought a decent dehumidifier and use that elsewhere to dry clothes (at the other end of the house in utlity room, so this wont contribute to the bedroom problem)

    wifes wanting to buy a fancy £250ish dehumidifier and stick it in the hallway. my response is, theres no condensation in the hallway, its our bedroom and the lads that are worst (outside north facing wall). these are just off the hallway, she says if we leave the doors open itll be the best solution.

    i say….. ill ask on here 🙂

    ive just taken the covers off the airbricks and hoovered them out, they were a little clogged with dust.
    id also guess that a small dehumidifier that fits under a bed may be the best way forwards, one in each bedroom. she says these dont exist.

    whats the most important consideration here, dehumidifying, or air movement?

    we’re also about to build some new wardrobes, but im wary of mould growing behind them over the months/years. would a blast of air from a fan maybe every week or so behind them prevent this? will a dehumidifier in the room (or hallway) pull moist air from behind wardrobes or not powerful enough?

    dont even get me started on the bathroom, crap extractor fan, radiator going rusty grrrrr……

    so many questions, i hope you have all the answers 😀

    thanks

    sharkbait
    Member

    Dehumidifiers are a [partial] solution to a problem caused by lack of air movement. Solve the latter and you [hopefully] won’t need the former.

    Do your windows open?

    had this problem a few years ago, with clothes going green in drawers under the bed, so got our builder to stick us a couple of airbricks in

    The thing is that those drawers are under the two of you and you’re giving off moisture – unless the drawers were open they wouldn’t get much air circulation.

    Premier Icon sadexpunk
    Subscriber

    a problem caused by lack of air movement. Solve the latter and you [hopefully] won’t need the former.

    so would a fan be more beneficial than a dehumidifier?

    Do your windows open?

    yes, and we do open them, we have trickle vents when closed, and often have them on the security vent setting where theyre just slightly open.

    aP
    Member

    I suspect that with that much moisture you have a water ingress problem rather than a condensation problem. Take a look at what’s immediately outside, and what condition gutters and downpipes are in, also drain gulleys etc.

    FunkyDunc
    Member

    Have you got cavity wall insulation?

    I would recommend PPV as above over dehumidifier any day, but does sound odd how damp it is

    Premier Icon matt_outandabout
    Subscriber

    I suspect that with that much moisture you have a water ingress problem rather than a condensation problem. Take a look at what’s immediately outside, and what condition gutters and downpipes are in, also drain gulleys etc.

    I would agree with this.
    We identified three issues:
    – drip from a gutter join splashing a wall
    – crack in render between extension and old house
    – the sh*te building materials, narrow cavity and lack of any insulation in part of the extension

    Sorting these solved half our damp/mould issues.

    We also have a decent dehumidifier. This gets moved around the house depending on where hasn’t had it or where the window condensation is forming. For reference, we have 5 of us in very small semi, so condensation build up even with vents etc overnight can be a problem.

    Premier Icon sadexpunk
    Subscriber

    I suspect that with that much moisture you have a water ingress problem rather than a condensation problem. Take a look at what’s immediately outside, and what condition gutters and downpipes are in, also drain gulleys etc.

    builder checked this all over and said it was defo condensation. there is no sign of damp on any walls (which i would expect from a guttering/drainpipe prob), just the floor and mould at low lying levels.
    there are no water pipes under the property, we checked that too and also looked at the water meter with everything turned off to see if it was still moving. it wasnt.

    yes we have cavity wall insulation which i am told can contribute, seems a fine balancing act between keeping warm and getting damp :-/

    Premier Icon BadlyWiredDog
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    Could you experiment with the dehumidifier you do have in the utility room and run it in the bedroom during the day? I’ve run a dehumidifier in two houses now – actually in one house, and an outhouse office – and we have one in the cellar and they do make a difference, but as per the poster above, if you’re sure there’s not a leak, I’d look at one of the Drimaster, loft-housed things.

    I’d also bear in mind that most dehumidifiers make a low hum or worse, while in operation, so you may not want one on when you’re in the bedroom, which in turn is when you’re creating the most moisture.

    Do you have extractor fans in the bathroom and kitchen btw, it all helps?

    Premier Icon oikeith
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    I’d look at the a loft based positive displacement wotsit

    A friend of mine had one of these, rated it except for said it was always chilly in the house.

    Moved into a new home in October and had constant wet windows to start with, window opening didn’t do very much as occurred mainly overnight, I think its mainly down to an under heated upstairs but clothes are dried upstairs on a horse too. As a temp fix We got a 12 Litre Dehumidifier and run it by drying clothes and also put it on for a few hours everynight on the landing with the doors open, has fixed it for us for now.

    Premier Icon jam bo
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    if there isnt a leak, then the moisture in the air that is condensing will be coming from the bathroom, the kitchen or from you. decent extractors in the bathroom/kitchen and a PPV unit in the loft will fix the problem.

    I only notice the cold air from my PPV if I stand directly below it at the top of the stairs. its made a massive difference to the house and how it feels. damp air isn’t good for you either and costs more to heat.

    grarea
    Member

    I suspect that with that much moisture you have a water ingress problem rather than a condensation problem.

    I know the guy said it wasn’t, but it does sound like a LOT of water.
    I would have a look around looking for holes as well.
    Over various propeties blah blah blah, I have seen:
    A drip from a gutter end cap on wrong.
    Holes in the wall adding moisture into the cavity.
    Cracks in render.
    Gaps around drains outside next to the house.
    A leak in the tiles round a shower tray leading to water and damp creeping under the floor to a cupboard.
    A shower leak running along a pipe out of sight to another point.
    A house with cheap pebble dashing covering up the air bricks.
    The ‘smelly pipe’ that went through the roof letting water in and it running down. agin into the cavity and then along the base of a wall.

    Another property was completely fine as I lived there, but it got really bad with the next person.
    The place had excellent windows etc. But they refused to open them.
    They would do a lot of vigorous boiling type cooking, had four people in a two bed flat,all had hot long showers with the window shut.
    Always had the heating right up.
    Caused a lot of damp and mould issues.

    Drying your washing indoors creates an awful lot of moisture in a house.

    Can be all sorts of things.

    I got a secondhand dehumidifier, it’ll do at least 7 litres a day (will need emptying every 8 hours if we have washing in the house) and will dry a whole rack of washing in 12 hours. At the same time it has prevented any mildew/mould growing in the colder corners of the room.

    You don’t need them in the damp room itself, you can run it on the hallway and the dryer air near the dehumidifier supposedly will encourage air movement as the house stays evenly humid.

    If I could be bothered, ours can be plumbed with a flexible pipe so it never needs emptying.

    joeydeacon
    Member

    We’ve got a drimaster – they’re great – cost nothing to run, very quiet, and our flat never smells of cooking etc due to the constant fresh air. Automatically shuts off in summer when the loft gets too warm. It does leave the hallway slightly colder, but it’s cheaper to heat dry air than humid air. A dehumidifier just helps temporarily deal with the problem, a drimaster (for us, and for my parents in their old cottage) eliminates 95% of the damp. If you’re worried about cold air, think they do one with a heater built in.

    5plusn8
    Member

    Has nobody mentioned an extractor fan? Do you have them in kitchen and bathrooms? That would be my no 1 place to start.
    In residential kitchens we normally fit an external routed fan over the hob, plus a humidstat one on the wall.
    edit – I see your bathroom one is dreadful, sort that out. Condensation spreads out so this could be part of your issue in the bedroom.
    If the bathroom hole is only 100mm then get a centrifigal jobby, they are excellent, this blauberg one is our current fave as its 123m3 per hour. Its sucks like a good un.
    https://www.blauberg.co.uk/en/blauberg-force-centrifugal-residential-fan-100mm-timer?

    wrightyson
    Member

    Which way do joists run, you could be getting joist end damp/rot on them caused by cavity insulation being soaked and up against them, this will cause you a world of pain if it is the case, get a floor board up and check.

    Premier Icon cynic-al
    Subscriber

    Are you heating the room enough?

    If you have the windows open a lot then the heat may be going straight out leaving cold walls for the condensation.

    Thought about internal wall insulation?

    5plusn8
    Member

    Cynical -al I am half with you – insulation is another one, if the walls are cold, then they will cause condensation.
    However open windows are good, not bad, we get horrific condensation in rooms where the tenants have lots of heating but no ventilation, eg they close the trickle vents and tape up the brick vents….

    Premier Icon sadexpunk
    Subscriber

    Do you have extractor fans in the bathroom and kitchen btw, it all helps?

    we do but theyre next to useless, token jobbies. ive watched steam near the bathroom one laugh in its face, and the kitchen one is one of those cooker hoods with a filter that doesnt lead to the outside.

    If the bathroom hole is only 100mm then get a centrifigal jobby, they are excellent, this blauberg one is our current fave as its 123m3 per hour. Its sucks like a good un.
    https://www.blauberg.co.uk/en/blauberg-force-centrifugal-residential-fan-100mm-timer?

    looks interesting, ill have to have a measure up of the hole weve got at present. its to an outside wall but just under the soffits. i assume all id need to supplement it would be a bit of plastic pipe?

    get a floor board up and check.

    no floorboards, we’re in a bungalow with concrete and floor tiles.

    im leaning with the extractors ^^^ at the minute, maybe a small dehumidifier under the bed if they exist? anyone know of any, or is my wife right? (as usual)

    thanks

    Premier Icon cynic-al
    Subscriber

    However open windows are good, not bad, we get horrific condensation in rooms where the tenants have lots of heating but no ventilation, eg they close the trickle vents and tape up the brick vents…

    It’s a balance…

    Cold walls and indoor living humidity creation.

    More heat, less internal moisture production (or better management) and insulation/ ventilation improvements where possible. As Jambo has said, it’s a balance.

    Given your air bricks were always wet, (cold spot) I’d say you have a problem with insufficient heat or excess humidity indoors.

    myti
    Member

    If it is condensation the positive pressure ventilation is what you want. I’ve got it in mine and a rental property and it works miraculously. No messing about with dehumidifiers. If it’s still a bit damp after a good few months get decent extractor fans put in bathroom and kitchen

    wrightyson
    Member

    Basic cold bridging going on then by the sounds of it, dew point being within the property. I’d hazard a guess there will be zero insulation under the concrete floors and down at the bottom of the wall due to mortar droppings during construction, current air outside has dropped cold, you’ve banged up the heating, add to that lack of air flow but warm under the bed and around the perimeter and you’ve got the perfect scenario. Positive pressure units can be very good at alleviating this but not always successful in the harder to reach places. I had all the same problems but really bad black mold behind wardrobes and anything up against a wall. Admittedly ive got 9 inch solid brickwork but i remedied by having every inch of plaster off and then insulated every external wall, I appreciate you may not want to do this but it is the only certain way by pushing the dew point further out.
    Edit, but that won’t help with the floor being cold…

    Premier Icon sadexpunk
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    Are you heating the room enough?

    probably not, its generally a fairly cold house, i dont like wasting heat so heatings only on when its really cold outside, or for 2 hour sessions say every now and then.

    ill take the cover off the bathroom fan and measure up, im defo leaning towards fans in the bathroom and kitchen anyway.

    this PPV lark, bout £300 yep? our loft is freezing (as youd expect) so im a bit wary of pushing freezing cold air into a house thats already cold and we’re trying to heat up.

    didnt really get an answer to an earlier question, would a blast from a desk fan every now and then behind wardrobes/static furniture solve any issues of walls going black behind them, spores etc? or does it need to be a more holistic approach, so extractors/PPV to prevent the moisture build up in the first place?

    any mileage in a small ‘under the bed’ dehumidifier that can run for a few hours in the mornings say? or leave bedroom doors open and bigger/betterer dehumidifier in hallway?

    thanks

    trail_rat
    Member

    The last thing you want in your bed room is a dehumidifier.

    I had a rental (as a tennents) where this was a solution to the fact it was on a noisy road and so the owner had blocked all the vents ….

    Anyway you need to sort this or you’ll end up with respiratory issues from the damp.

    Premier Icon sadexpunk
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    The last thing you want in your bed room is a dehumidifier.

    why? i agree i wouldnt want it on whilst sleeping, but once up and at em, why not have one to remove the night moisture around the bed for an hour or two?

    myti
    Member

    It’s freezing in my loft too but the unit is in the hall and that’s the only place I notice it being slightly cooler. As others have said it’s easier to heat dry air than damp air but it does sound like you might want your heating on a bit more. Piv was no more than £300 fitted easily ourselves and if you’re really worried about cold air you can get the one which warms the air before pushing it in. This is what I have in the rented property but in my own it’s not heated. Our bedroom in the eaves is very poorly insulated and noticeably colder than the rest of the house which was where the black mould was worst as the moist air finds the coldest places to condense. Also if you’re worried about running costs I would think several dehumidifiers would cost much more to run and more faff than one Piv unit. Seems silly to use something to remove moisture from the air when you could just push that moist air out of your house instead.

    5plusn8
    Member

    q’s
    Where are your kitchen and bathroom in relation to the problem room?
    Which walls in the problem room are external?

    PPS we have fitted 4 of those PPV units over the years without real success, improved extraction fixes it for us. With tenants we use humidistats on some fans to take it out of their control, as nobody leaves them on for long enough. So if you do fit better fans, make sure you train everyone at home to use them properly.
    We did use to have a £200 hand held humidity meter to show tenants how the fan would improve things. The electrician would spend an hour or so running the shower for 5 mins, and then the fan and monitoring the humidity (only works with cooperative tenants). We have less problems now and I haven’t needed the thing for years. Which one of you has nicked it?

    Premier Icon timmys
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    Where’s this stuff about an under bed dehumidifier coming from? Seems very unlikely that such a thing would exist.

    I’ve been very pleased with our PPV – with the slight caveat that if I was doing it again I think I’d go for one which has the option of heating the air.

    Premier Icon verses
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    Our “normal” upright dehumidifier has a filter that gets clogged with dust and needs cleaning every few weeks (once a month). I’d imagine one under the bed (if it exists) would need its filter cleaning daily!

    We also fitted a PPV a few years ago, it’s infinitely cheaper to run than the dehumidifier was, and actually succeeds at drying out the whole house. I moved a bookcase before xmas and there wasn’t a single mould spot behind it, we’ve been in the house 18 years and that’s never happened before.

    EDIT: Anyone want to buy a dehumidifier 😀

    Premier Icon sadexpunk
    Subscriber

    Where are your kitchen and bathroom in relation to the problem room?
    Which walls in the problem room are external?

    rough diagram, not to scale and slightly wrong but you get the picture….

    house plan

    ive taken a few pics and unscrewed the extractor cover to have a measure….
    bathroom extractor looks to be 90mm and as its too high to vent directly through brick, seems to be connected by way of tumble dryer flexi hose to the soffits.

    extractor

    as you can see by the outside view, the soffits are too low for it to go directly out in a straight line.

    outside

    flexi hose

    EDIT: yes i know the soffits could do with a clean 😉

    EDIT: EDIT:

    I’d imagine one under the bed (if it exists) would need its filter cleaning daily!

    wouldnt that be a good sign that its shite that you havent breathed in?

    Premier Icon gkeeffe
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    Dehumidifiers don’t work – all air carries moisture, and every hour the air change brings in more wet air, so it looks like you’re drying the room, but you’re not, you’re maintaining the status quo at best.

    Warming the fabric of the house is best. Condensation will occur on the coldest surface in the room regardless. Air movement isn’t so important re condensation – except that most warming is by convection so often places with no air movement are coldest.

    Usually these problems occur after double glazing, as before the single glazing was the coldest surface in the room, and after it isn’t.

    Best solutions

    – don’t produce any moisture in the house – short shower with window open, no boiling of food without pan lid and extract on, no drying of clothes in the house.

    – warm surfaces of the house – keep the heating on.

    – let air circulate under beds

    – insulate surfaces esp North-facing walls internally until the windows are the coldest surface – condensation will happen on them then, and that’s easy to deal with.

    Premier Icon verses
    Subscriber

    wouldnt that be a good sign that its shite that you havent breathed in?

    The filter gets clogged with dust, not with mould/spores.

    our loft is freezing (as youd expect) so im a bit wary of pushing freezing cold air into a house thats already cold and we’re trying to heat up.

    The unit inlcudes a heating element.

    Premier Icon mick_r
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    Parent’s house has used ppv for 40 years and it fixed things that extra vents, heating etc didn’t touch.

    Same for our house for the last 15 years.

    It is cheap and simple to install. If you don’t like it then easy to remove (one hole in plasterboard) and can probably sell on ebay for almost what you bought it for.

    grantway
    Member

    What type of external wall do you have IE cavity or brick built?
    If it is brick built has it been plastered in modern gypsum plaster?

    Premier Icon cynic-al
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    i dont like wasting heat so heatings only on when its really cold outside, or for 2 hour sessions say every now and then.

    This is a likly to be a big part of your problem.

    PPV may be a cheaper solution than heating it tho. I’ve only seen one client with a PPV device and she hated it – it was really drafty – but her home was hard to heat.

    Given it’s the cheapest thing to try, why not just clear out all the stuff from under the beds so air can circulate and leave the heating on 24/7 with the thermostat set appropriately rather than acting as a human thermostat and switching it on when it feels cold?

    5plusn8
    Member

    That 90mm is probably a 100mm hole, you defo want the centrifugal fan as they are better for long runs, yours looks to have one bend but its a bit of a crap route. If you can get in there, get rid of the flexy and fit rigid plastic it flows better, you could also see about exiting through the roof rather than under the soffit. Depending on your roof construction you might need a lead slate. This is a cheap assed one, I would not contemplate fitting, but it shows you what its for.

    My experience is as an accounting manager for a property management and refurb company who ends up having to solve all this stuff as nobody else will take responsibility.
    I deal with the complaints, instruct the contractors, and pay the bills, so my experience is purely anecdotal about what we have spent and whether the problems have returned.
    I reckon the reason why extraction “does not seem to touch it” is that it has been installed badly, is a crap fan, and isn’t used enough. So ppv can get around all that, however decent extraction will move more air when it is needed.
    I deal with the complaints, instruct the contractors, and pay the bills, so my experience is purely anecdotal about what we have spent and whether the problems have returned.

    Premier Icon sadexpunk
    Subscriber

    The unit inlcudes a heating element.

    which id be very scared of then, as that means itd be on 24/7 as the loft will never get warm enough to pump warm air through on its own?

    What type of external wall do you have IE cavity or brick built?
    If it is brick built has it been plastered in modern gypsum plaster?

    yeah double brick with cavity wall insulation and bog standard plaster.

    PPV may be a cheaper solution than heating it tho.

    if the bumph is to be believed then id need both wouldnt i? house will be having cold air (unless heated in the loft 24/7) pumped around and the heating would be working harder to warm the house because of this?

    Given it’s the cheapest thing to try, why not just clear out all the stuff from under the beds so air can circulate and leave the heating on 24/7 with the thermostat set appropriately rather than acting as a human thermostat and switching it on when it feels cold?

    leaving the heating on 24/7 would give me astronomical bills id say. its not the warmest house in the world :-/

    That 90mm is probably a 100mm hole, you defo want the centrifugal fan as they are better for long runs, yours looks to have one bend but its a bit of a crap route. If you can get in there, get rid of the flexy and fit rigid plastic it flows better, you could also see about exiting through the roof rather than under the soffit. Depending on your roof construction you might need a lead slate. This is a cheap assed one, I would not contemplate fitting, but it shows you what its for.

    ill look into this, the extractor still feels needed whether we go PPV or not, the bathroom is very damp and so’s the kitchen at cooking times.
    ill have to start stripping it i think and see what i can do, just dont want to take it to bits, leave the wiring dangling loose (its probs on either lighting or ring main so cant be isolated in itself), holes in the wall etc until ive got the equipment to fix it properly….

    thanks

    EDIT: if i bought that extractor linked above ^^^, what pipe should i be buying from the builders merchants, 100mm waste pipe or summats?
    and out of the choices (timer, humidity etc) would i be better with humidity? then itll always be on until the moisture goes?
    thanks

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