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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

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    • CommentAuthorwellburn
    • CommentTimeApr 6th 2019
     
    I do enjoy a bath ... and the water is often shared, BUT - A lot of hot water is still let away.
    In winter / heating season, could this easily (ie cheaply) be re-used?

    I could let it go cold in the bathroom, but that would be bad bad bad for humidity...
    I could maybe have a plastic cover over the bath, so it gives out heat as it cools down, WITHOUT releasing steam ....
    What about having an old radiator in the room below, on the bathwater waste? - bath empties through the radiator, transferes some heat, used for heating the room below?
    I imagine the ecosystem inside that old radiator could become quite unhealthy ...

    Am doing a full refit, and just wondered ....
    any ideas
    • CommentAuthortony
    • CommentTimeApr 6th 2019
     
    Leaving water in the bath is the simplest and best idea.
    • CommentAuthorwellburn
    • CommentTimeApr 6th 2019
     
    yes, but it would be great to have a giant elasticated cover to slip over and keep the steam in....
    •  
      CommentAuthordjh
    • CommentTimeApr 6th 2019
     
    If you're doing a full refit, have you considered ventilation? There are no concerns about humidity with an MVHR system.
  1.  
    Water left in the bath cools mostly by evaporation.

    Tony has MHRV, so he can recover a little of the bath heat as the latent heat when the water vapour condenses in his exchanger.

    I only have an extractor fan, so I have to waste extra electricity to vent out the humidity, I get the bath drained and squeegeed as quick as possible after bathing several children in it, as infrequently as is decent.

    A 100 litre bath cooled from say 30degC to room temp contains 100* 4.2 * 10 /3600 = about 1 kWh of heat, worth about 6p, depending how you heat the house, so I couldn't justify spending big money on plumbing to recover it.

    (Edit: However if it were cooled close to the incoming mains water temperature, it could release twice as much energy - ie pre heat the cold feed to the hot water system)

    Others have made homebrew pipe in pipe exchangers to heat the cold feed to their shower using the waste, but we can't store the recovered heat for next week's bath like this...!
    •  
      CommentAuthordjh
    • CommentTimeApr 6th 2019
     
    Posted By: WillInAberdeenWater left in the bath cools mostly by evaporation.

    Indeed, though foam on the top helps a bit to insulate. A thin layer of oil on top slows evaporation.
  2.  
    •  
      CommentAuthorfostertom
    • CommentTimeApr 8th 2019
     
    'Grey' waste water, even bath water that seems clean enough that
    Posted By: wellburnthe water is often shared
    is full of active organic matter and it's a challenge to handle that such that the inevitable scum and growth is contained without causing problem. Think of inside of waste pipes, traps etc. So not a gd idea to feed it through radiators!
    • CommentAuthorphiledge
    • CommentTimeApr 8th 2019
     
    If you just lift the plug a little and let the water trickle out, the slow flow of water would probably give up much/most of its heat into the internal waste pipes??
    • CommentAuthortony
    • CommentTimeApr 9th 2019
     
    Not as good as leaving in the bath to cool right down to room temperature.
    • CommentAuthorgyrogear
    • CommentTimeApr 9th 2019
     
    ah! for the days of cast-iron bath-tubs - none of this acrylic stuff !

    gg
    • CommentAuthortony
    • CommentTimeApr 9th 2019
     
    It makes no difference, the heat all still goes into the house
    •  
      CommentAuthordjh
    • CommentTimeApr 9th 2019
     
    Insulating a bath is a good thing to do, since it reduces the hot water draw needed to keep the tub hot, and it also minimises the total energy used, whether in winter or summer.
    • CommentAuthorowlman
    • CommentTimeApr 9th 2019 edited
     
    <blockquote><cite>Posted By: tony</cite>Leaving water in the bath is the simplest and best idea.</blockquote>

    <blockquote><cite>Posted By: wellburn</cite>yes, but it would be great to have a giant elasticated cover to slip over and keep the steam in....</blockquote>

    A few quids worth of this may help?

    https://www.poolandspacentre.co.uk/products/geo-bubble-pool-covers.html?gclid=EAIaIQobChMI8ru77ZnD4QIVi-F3Ch1aWgPPEAQYAyABEgJeoPD_BwE
    • CommentAuthortony
    • CommentTimeApr 9th 2019
     
    Or a couple of bits of used packaging
    • CommentAuthorMike1
    • CommentTimeApr 9th 2019
     
    For showers, worth knowing that you can buy heat exchangers that fit on the waste and warm the shower cold water supply. But ridiculously long payback period last time I looked into them.
  3.  
    "Insulating a bath is a good thing to do, since it reduces the hot water draw needed to keep the tub hot, and it also minimises the total energy used, whether in winter or summer."

    We spent a lot on our bath but don't regret the investment - made of this stuff https://www.cabuchon.com/cabuchon-quality/#ficore which they claim "keep the water hot over six times longer than acrylic and over twelve times longer than vitreous enamelled metal"

    I was dubious but it really seems to work - It is very noticable how warm the water remains even after a long bath.

    Whats the best way of getting the same effect with a bath made of another material? Just stuff the space underneath with mineral wool?
    • CommentAuthorbhommels
    • CommentTimeApr 30th 2019 edited
     
    Posted By: Simon Still

    I was dubious but it really seems to work - It is very noticable how warm the water remains even after a long bath.

    Whats the best way of getting the same effect with a bath made of another material? Just stuff the space underneath with mineral wool?


    Under the bath I keep the spare tiles, and the rest of the void is stuffed with binbags full of used packaging material: bubblewrap, polystyrene peanuts, whatever.
    •  
      CommentAuthordjh
    • CommentTimeApr 30th 2019
     
    Posted By: Simon StillWhats the best way of getting the same effect with a bath made of another material? Just stuff the space underneath with mineral wool?

    That's what I did with our plastic bath, although with recycled plastic wool IIRC - easier on the hands. I doubt there's anything you can do with a metal bath except replace it - the conductivity is so high that heat will just move to the exposed surfaces.
  4.  
    If insulation under the bath means the floor or wall will be much cooler than the bathroom air, then think about excluding condensation from under the insulation.

    We had masonry walls and solid floor under the bath which we insulated, but they got 'sweaty' underneath the insulation. Subsequently I insulated under there with kingspan offcuts, with a silicone bead round each edge to keep the water vapour out.
  5.  
    <blockquote><cite>Posted By: owlman</cite><blockquote><cite>Posted By: tony</cite>Leaving water in the bath is the simplest and best idea.</blockquote>

    <blockquote><cite>Posted By: wellburn</cite>yes, but it would be great to have a giant elasticated cover to slip over and keep the steam in....</blockquote>

    A few quids worth of this may help?

    <a href="https://www.poolandspacentre.co.uk/products/geo-bubble-pool-covers.html?gclid=EAIaIQobChMI8ru77ZnD4QIVi-F3Ch1aWgPPEAQYAyABEgJeoPD_BwE" rel="nofollow">https://www.poolandspacentre.co.uk/products/geo-bubble-pool-covers.html?gclid=EAIaIQobChMI8ru77ZnD4QIVi-F3Ch1aWgPPEAQYAyABEgJeoPD_BwE</a></blockquote>



    I've sometimes thought about that, but the problem with a floating cover is that the surface area varies a lot depending on the water depth, as the sides slope.
    I like the idea of an elasticated cover - perfect for a free-standing roll-top bath.

    It doesn't really need to insulate at all, just be non-breathable so that water vapour can't escape. The heat would escape into the house, but the moisture would be contained.
    It would be especially useful when sharing baths with a delay between users.
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