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  1.  
    I have a bungalow facing south, which I'm renovating bit by bit. The front of the house has a decent sized sun lounge which collects a nice amount of solar gain, which convects nicely in to the living space just behind. Although mostly uninsulated, even overcast days are reasonably comfortable at the front.

    However, the bedrooms being a couple rooms further back are naturally much colder (lounge is currently 18C, furthest back bedroom is 12C). The bedroom I've just finished renovating is very well insulated and keeps its heat well enough, but the room behind, the third bedroom extension that's sheltered from the sun almost entirely is never naturally particularly warm. I've considered running ducting with an in-line fan and thermostat from the sun lounge to spread the heat around on warmer days, and I may well do this at some point.

    Although the lack of warmth at the back doesn't particularly bother me (I don't particularly like the bedrooms warm anyway, I leave the windows cracked open all year round), what is a concern is keeping humidity at a safe level. I've read that above 65% RH, mould can begin to form (the back bedroom is currently 12C, 75% RH, outside is 11C and 93% RH). Anything from 12C to 25C and I'm happy enough not to need any heating on and have windows open, and for the other 9 months or so of the year ventilating a little less and keeping the place comfortable by means of a wood burning stove at the front of the house, of course causing humidity levels to drop significantly internally (I've got a stat in each room to keep an eye on this, I've become a bit paranoid).

    Of course, during the summer months (or weeks) humidity will naturally rise internally, so why isn't summertime humidity a problem?

    At what point am I going to introduce mould? Presumably when a surface somewhere in the house drops below the dew point. Currently, the single glazing on cold evenings suffers from this (obviously), along with the back bedroom asphalt floor, which I've now insulated, VCL'd and laid a floating chipboard floor on which has so far stopped this.

    So with this in mind, what steps must I take to ensure I don't make my house mouldy?! I don't particularly want to leave a heater on in the colder rooms all through the year as the heat is totally unnecessary to the occupants, but is this the sensible approach?

    Sorry about the slightly messy rant.
    • CommentAuthorringi
    • CommentTimeMay 27th 2016
     
    One option is to put in a MVHR system, sucking air out of the warm part of the house (I assume that is near the kitchen) and putting the fresh pre-warmed air into the cold part. You do not need to do a full install of a MRVH with outsets in every room, for them to work well.

    Then close the windows in the cold rooms, as they now get fresh air from the MVHR system, this will make these rooms a little warmer.

    (Do you not want to move the warm air directly into the cold rooms, as that will tend to increase your HR, as the warm damp air cools.)

    Also where do you dry your washing?
  2.  
    Ok, MVHR sounds like a sensible solution, extracting from the sun lounge and bathroom and feeding to the back of the house. I've seen these systems for around £300 on eBay, would that do the trick?

    Washing is dried in the conservatory - the windows in there are permanently open and the door to the house is always closed. Humidity from the household is really no problem at all, just that which is naturally in the outside air.
  3.  
    Posted By: ringiOne option is to put in a MVHR system, sucking air out of the warm part of the house (I assume that is near the kitchen) and putting the fresh pre-warmed air into the cold part.

    Posted By: alexoftheorchardOk, MVHR sounds like a sensible solution, extracting from the sun lounge and bathroom and feeding to the back of the house. I've seen these systems for around £300 on eBay, would that do the trick?

    Quite a few threads and posts on here the bottom line of which is you can't use MVHR to move heat around a house, it just doesn't move enough air to usefully move heat.
    • CommentAuthorEd Davies
    • CommentTimeMay 27th 2016 edited
     
    If this is a temporary problem pending refurbishment of those rooms maybe a dehumidifier would help. Provides a bit of heat too; a little more than an electric heater using the same power.

    To work well in a cool room you need an absorption type. Following the recommendation of some friends I got an Ecoair DD1 Simple from Amazon and have been very pleased with it - helps a lot to keep the static caravan I'm staying in dry. Others on here have recommended larger ones in the same range.
  4.  
    Well the thing is, I'm not sure there even is a problem. The temp differential doesn't bother me, I'm just concerned about the effects of increased humidity. My question is more along the lines of do I need to worry about stabilising temperature in the colder rooms? As far as I can see, I just need to keep all surfaces above the dew point?

    The furthest north room was the first one I renovated, a brick cavity extension.
  5.  
    Posted By: alexoftheorchardWell the thing is, I'm not sure there even is a problem.

    If it ain't broke - don't fix it !!

    If you get problems it is more likely to be in the winter, keep an eye on things especially in the corners and behind any furniture against outside walls and at the first sign of problems start applying the fixes
    • CommentAuthorringi
    • CommentTimeMay 27th 2016
     
    Posted By: Peter_in_HungaryQuite a few threads and posts on here the bottom line of which is you can't use MVHR to move heat around a house, it just doesn't move enough air to usefully move heat.


    Agreed if you want the heat for "heating", but I expect having the veneration air coming into the cold room at 16c rather then however cold it is outside would make a big difference to the risk of condensation. At present the coldest are is coming in right next to the windows.

    I would not expect much more then a 1c change in the over all temp of the coldest room given how little heat a MVHR system moves, but add this small improvement, to a reduction in the water content due to removing wet air from the kitchen, and it would make a big difference.
    •  
      CommentAuthordjh
    • CommentTimeMay 28th 2016
     
    Posted By: Peter_in_HungaryIf it ain't broke - don't fix it !!

    If you get problems it is more likely to be in the winter, keep an eye on things especially in the corners and behind any furniture against outside walls and at the first sign of problems start applying the fixes

    Exactly.

    If you have a wardrobe against a wall, then behind it or underneath it are likely places. Basically anywhere it is difficult for you to check! Move furniture away from the walls a bit. The single-glazed windows are helping you by condensing water out of the air before it starts condensing anywhere else.

    If you do need a cure where mould turns out to be a problem then I'd suggest one or more of a dehumidifier, a bit of extra heat, and stirring the air up (i.e. a fan rather than an MVHR designed not to disturb the air, or opening the windows wide for an hour).
  6.  
    DJH, sorry if my initial post was a bit vague, but this room does not have single glazing. This cold room was refurbished last year with a new double glazed window to the east side. Being an extension to the rear of the property, it has three outside walls, and rarely sees much sun. To the outside of the extension is a 3ft walkway, and then rising retaining walls for the upper garden, so the north side is permanently shaded.

    When we first bought the house, this room was derelict. The flat roof had failed allowing it to rain indoors, the exterior render had blown off the common bricks and the inside dry-lining was sodden. I took the whole thing back to brick (including the render behind the dry lining which was likely an early attempt at 'damp proofing'), dried it out for a few months and put everything back together. The whole extension is peppered in cavity vents, presumably to solve moisture problems that builders assumed were caused by damp penetration, but was more likely the render stopping anything from breathing. I'm yet to re-render the outside, it's just exposed brick with an empty cavity - I may fill this cavity with beads, block up the vents and DIY EWI it when I get around to it.

    Anyway, this room is accessed from the bedroom I've just refurbished (much talked about on this forum), and as things stand, neither are yet being lived in. It's the remainder of the house that has single glazing, and they all of course get coated in condensation on colder days.

    I'm already ventilating the house an awful lot more than most, leaving windows wide open and even tend to have exterior doors open on nice days. I'm probably ventilating too much. I've got a low energy dehumidifier that we used to dry the house out after 5 years of standing empty and sealed up last year, so I could leave this running on a timer for a few hours per day, but I'd rather a long term preventative solution (if indeed there is a problem). My only cause for concern at the moment is the higher RH readings - I suppose a bit of year round background heat would be wise, but costly.
    • CommentAuthorGreenfish
    • CommentTimeMay 29th 2016
     
    To recap - you have an unused, unheated and naturally cold room and you want to avoid mould. But you are not sure there is a problem so don't want to spend money unnecessarily.

    Because the room is unused man-made humidity e.g. breathing, drying washing etc. is not an issue, but it will be effected by the natural moisture in the air. Where are you located? Places like Cornwall where I am have amazingly damp springs and autumns (and winters), other places are far dryer. In autumn and spring, times when indoor and outdoor temps are similar, I can easily get RH well over 60%

    MVHR was suggested, well in my experience that just ensures that the RH inside tracks the RH outside. MVHR is not air-conditioning, neither is it a good way to move heat (compared to water based heating systems). It is good at removing additional "contanients" (moisture, gases and ordours) produced by humans and pets etc. without heat loss from the house, but will bring inside whatever is outside. Initial concerns about RH readings in my new build made me consider turning off the MVHR when outside was Cornish mizzle, then I worried about power cycling lifing the unit and didn't. So either I live with the natural high RH I have imported or I heat up the house until the mizzle stops.

    In time I am learning not to panic about trying to keep the rooms below 60% RH (but not too low either). All of Cornwall must break this "rule" from time to time unless they have air-con. In figure now that if the source is nature it is OK, only the peaks caused by human agency e.g. drying washing or having a shower need action. Anyway my house walls are now "warm", or rather well insulated so the surface doesn't have cold spots that condensation loves.

    Lucky me! But back to the OP.

    To avoid mould means to avoid lingering condensation. You can avoid condensation this by locally reducing RH by either heating the walls, or removing the moisture from the air (or both). But IMO the issue biggest issue is the local "lingering". In my old cold walled house mould happened even in heated rooms in the "furniture shadows" e.g. behind the wardrobe or anything near a wall.

    My advice is not to just ventilate i.e. let air into the room, but to ensure that the cold walls get a good flow of air over them. The dryer that air can be the better, but movement is the key. Help that with furniture layout perhaps, use vents to create a flow or maybe even get some low power fans. I even wonder what fans could achieve moving air in an room without ventilation (that could just as easily be importing moisture as taking it out).
  7.  
    Some interesting points Greenfish.

    I do often wonder about these RH recommendations as they're impossible to achieve during the warmer months as the house will simply equalise with the outside RH (assuming cooling or heating isn't required), or be slightly above if ventilation isn't ideal. I had wondered how useful MVHR could be at reducing humidity.

    The room is currently unused, and has been refurbished but redundant up until the point the room that leads to it is complete, which it now is, so I'll be using both of these rooms once the carpet goes in sometime next week. This cold 'problem' room will be used as a dressing room, but typically won't require much heat for our comfort beyond an hour in the morning. There's a 1kw convector rad fitted to the wall with a timer, so I can set this to keep the room stable at say 12 degrees + all year round with a little extra in the mornings, but I'm concerned that being the cold spot of the house it'll attract humidity with ease. I should probably insulate the cavity and EWI it and leave the thermostat on 16 or so all year really.

    I'm in Northumberland on the edge of a hill, sheltered from the north and completely exposed to the south. It's either very windy or eerily still, and typically one of the drier parts of the country.

    I'll have two large wardrobes (against outside walls) and a couple of chairs in there, but not much else. I can stand these wardrobes off the walls a little, but I'm unsure how I can practically get air circulating in the room without a low energy ceiling fan or similar.
    • CommentAuthorgyrogear
    • CommentTimeMay 29th 2016 edited
     
    AoTO, as I see it, you are already on the right track by cracking that window open !

    Could you try pulling air into the back rooms, but from another (cooler) part of the house than your South-Facing lounge ?. Say, for example, from an upstairs space... Might also give you a shorter run (in the best case, requiring no duct, just an air grille...).

    Alternately, a floor-mounted "sweep" (= a little desk fan, on a timer maybe...), pushing air OUT of that bedroom (and therefore encouraging warmer (ceiling-level) air to come in, sort-of assisted convection...

    Also, does the DG in the back room have trickle vents in by any chance ?
    (just a bit better for security, perhaps, than leaving the window on the hook...)

    gg
    • CommentAuthortony
    • CommentTimeMay 29th 2016
     
    Re bringing in air from outside that is more "humid" than inside, that is almost never going to happen. The exception would be during a very warm humid period and we rarely get those.
  8.  
    Gyrogear, unfortunately there's no upstairs space (except for the loft) as its a bungalow. I could introduce a wall vent between the west facing bedroom and the cold extension (the room in question sits behind both the east (now refurbished) and west facing bedroom), but I'm not sure how effective that would be. It would likely create a through draft though.

    I suppose a low energy ceiling fan (if there is such a thing) would keep the air nicely stirred up.

    The DG doesn't have trickle vents in this room, I tend to leave the window open permanently with it cracked open and locked on the night latch instead, so couldn't see the point in specifying a trickle vent. Security isn't the biggest consideration here, if anyone unknown so much as walks down the road it'll be talk of the hamlet for a day or two.
    • CommentAuthorgyrogear
    • CommentTimeMay 29th 2016 edited
     
    Loft air could be just the thing...

    +1 for a low-power ceiling fan, if you can find one. Otherwise a decent (7-inch) PC case fan, on a transformer or a battery pack...

    gg
    • CommentAuthorGreenfish
    • CommentTimeMay 30th 2016 edited
     
    Posted By: tonyRe bringing in air from outside that is more "humid" than inside, that is almost never going to happen. The exception would be during a very warm humid period and we rarely get those.

    Try visiting moist Cornwall in the autumn/spring. Outside RH > 85% at 16C is not unusual, far from tropical but plenty of moisture in the air all the same.

    If you have ventilatied cooler rooms, unlikely in a nice insulated air-tight house like yours Tony but easy in an older or lower spec one, then the indoor RH will be near those heights too. Living at 20C plus it is not an issue of course. Likewise in convectively heated homes measuring room RH looks fine meanwhile there can be localised cold spots and condensation happening (that the convective currents can mostly soon dry unless furniture gets in the way).

    AotT as the room is a dressing room with wardrobes against the wall can I suggest you insulate the back of the wardrobes. In our old solid brick wall house with a built in wardrobe any items of clothing against the outer wall would eventually get mouldy. The room was heated but the walls always cold to touch. I applied 10mm of insulation board inside the wardrobe and never had any more mould issue there. The "furniture shadows" elsewhere in the room were always an issue especially in the bay window.
    • CommentAuthorCX23882
    • CommentTimeMay 30th 2016
     
    Not Cornwall but...

    I've had nearly a year living with a Nuaire Drimaster 365 PIV unit, fitted in the loft of my early 70's bungalow. The Drimaster 365 takes air from the loft space through the winter, and from late spring through early autumn, through a soffit vent on the north face (cooler air). Prior to fitting, I had awful problems with humidity - on the worst nights, the bedroom window would be streaming from top to bottom (this is with 1 person, no dogs etc), and every other window would have at least 2-3 inches of drippy condensation (not just a mist). The windows are around 20 years old, but uPVC double glazed, and the blinds weren't particularly tight fitting - in fact most of the time, I left them up. It didn't matter how long the heating was left on for - leaving it at 20C all night did nothing to help. Leaving every window locked open 24/7 (which is not the best idea in the bungalow) made no appreciable difference. There was mildew forming on the bed slats where the mattress sat on them - that was the last straw that made me pull the trigger on the unit.

    Since fitting the PIV unit, there have been no problems at all. In fact, I noticed the improvement straight away. The relative humidity does not measure that much lower than before (but maybe the cheapo temperature/humidity sensor is not accurate), but in spite of this there is no condensation anywhere. Every window is dry in the morning. The bathroom clears of steam from the shower within minutes. No mould or mildew forming anywhere, not even in the corners of shower cubicles etc. The bed slats have stayed free of mildew.

    I fitted some trickle vents in advantageous locations a few weeks after installing the Drimaster. They weren't actually needed to stop the condensation, but they do allow an element of control over where the air moves to. The ones I fitted are automatic, similar mechanism to Passivent ceiling vents, and a lot of the time, they close themselves because the relative humidity is low enough.

    The area where the ceiling diffuser is fitted doesn't feel any cooler. If I turn on the boost switch in the middle of winter, sure, cold air blows down the walls, but at the correct speed for the size of property (and with the diffuser sited the correct distance from the walls), it's fine. There is a heater option, but I didn't go for that (truly is wasteful in my opinion).

    My gas bill is lower than in previous years, even though I am effectively blowing hot air straight out of the trickle vents. It goes to show that it's really not as bad as it sounds.
    • CommentAuthortony
    • CommentTimeMay 30th 2016
     
    Quote "My gas bill is lower than in previous years, even though I am effectively blowing hot air straight out of the trickle vents. It goes to show that it's really not as bad as it sounds."

    Yea but er but that is not a direct comparison, this was a warm winter, blowing hot air out is not great, much better to recover the heat from it.
    • CommentAuthorCX23882
    • CommentTimeMay 30th 2016
     
    It has not been that much warmer. Go back another year and the first 3 months of the year are very similar to 2016. I have the gas usage figures because I tracked them every month since I moved in.

    The flow rate of PIV is so low that it doesn't cool down the property by any significant amount. And the added bonus is that the cold air is not coming IN through the windows. I do not feel any drafts. Cooking and animal dirt tray smells dissipate quickly.

    To fit MVHR would have cost at least 4 times the Drimaster. To be honest the basic Drimaster would probably have done the job too, and here it's an order of magnitude cost difference. The efficiency savings would never result in a reasonable payback period. Just as digging up my concrete floors to insulate them wouldn't, or replacing all existing DGU with low e units.

    I am not denying that MVHR is the Rolls Royce solution.
    • CommentAuthorringi
    • CommentTimeMay 30th 2016
     
    @Tony,

    The "key" with PIV is "I do not feel any drafts" unlike opening windows. Therefore people are often happy to turn down the heating a bit when they have PIV installed. When PIV have been installed by socal landlords, it has worked very well.

    Given the option I would always choose MVHR if I was planning to live somewhere for a long time, but PIV is a very good 2nd best option compared to having windows open most of the time.
  9.  
    Tony, outside air is typically anywhere from 40-100% RH year round. Once the air no longer needs warming internally, internal RH equalises with external, so summertime internal RH can register very high even with excellent ventilation (unless you run a dehumidifier or air con).

    Greenfish, good idea. I've got some spare 10mm XPS sheets I can line the back of the wardrobes with. I've seen some low energy wardrobe heaters (consuming about 40W) on Amazon too, these could work well to help protect the clothes!

    CX, I've looked at the PIV systems. I was ready to purchase up until the point I found an equal number of negative reviews. In principle it sounds very sensible, especially as our loft gets very warm from the solar gain pretty much all year being in an exposed position. The only downside is the fact the units switch off at 23 degrees, so I'd need a 365 unit to operate effectively when the sun's shining.

    Ringi, I've found a number of MVHR units for a few hundred on eBay. Are any of these up to the job? The posh ones are massively expensive in comparisons, so I'm wondering what the cheaper units sacrifice?
    • CommentAuthorgravelld
    • CommentTimeMay 31st 2016
     
    Problem I have with those PIV units are twofold:

    1) I don't want to be breathing air from my loft, there's horrible stuff up there.
    2) It still implies your permeability is high, which is a bad thing.

    With (2) I guess it comes down to what might be achievable and how that fits in with your plans for the house.
    • CommentAuthorgravelld
    • CommentTimeMay 31st 2016
     
    What about the ductless HR systems? E.g. Lunos.

    I think you should be thinking about a "system" long term, and just solve short term problems with a dehumidifier.
    • CommentAuthorringi
    • CommentTimeMay 31st 2016
     
    Posted By: alexoftheorchardRingi, I've found a number of MVHR units for a few hundred on eBay. Are any of these up to the job? The posh ones are massively expensive in comparisons, so I'm wondering what the cheaper units sacrifice?


    The cheap units may use more power to run their fan, they may also give out more noise, and they will not recover as much heat. I would not use a cheap unit for a "full" install, but would consider them if I was only putting in 2 or 3 outlets.
  10.  
    Gravelled, I've looked at the one room HR ventilators, but given the cost I could install a whole house system for the same price. Putting ducts in would be simple enough given that I'm working with a bungalow.

    The PIV systems are very well filtered, so the nasties above wouldn't reach the living space. In principle I'd prefer outside air ducted straight in.
    • CommentAuthorringi
    • CommentTimeMay 31st 2016
     
    Posted By: alexoftheorchard.I've looked at the PIV systems. ...... The only downside is the fact the units switch off at 23 degrees, so I'd need a 365 unit to operate effectively when the sun's shining.


    You don't want heated air being put into your home when it is very hot, as your home is likely to overheat. However when it is that hot, condensation tends not to be an issue, if you open windows.
    • CommentAuthorgravelld
    • CommentTimeMay 31st 2016
     
    I wasn't talking about the SRHRV systems, I meant ductless whole house HRV, but if you have no impediment against MVHR ducting then go with that, it'll be cheaper.
  11.  
    Ringi, it's been in the 20s up there whilst 0 outside when the sun's shining. Some of which was likely heat loss from the house, admittedly. The point I'm making is the standard Drimaster wouldn't do the trick in my house, I'd have to stump for the more expensive 365.
    •  
      CommentAuthordjh
    • CommentTimeMay 31st 2016
     
    Posted By: alexoftheorchardRingi, it's been in the 20s up there whilst 0 outside when the sun's shining. Some of which was likely heat loss from the house, admittedly. The point I'm making is the standard Drimaster wouldn't do the trick in my house, I'd have to stump for the more expensive 365.

    You may be right, but if the air in the loft is relatively still it can get quite hot whereas if it is moving through, perhaps being 'sucked' through by a PIV unit, then it won't have the chance to get as hot. I don't know how you could test which unt was needed.

    How easy is it to change the filters? Are they washable or do you need to buy new ones every time?
   
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