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Window u-values - how do they relate to heating costs

  • 24-05-2015 8:44pm
    #1
    Jane98
    Registered Users, Registered Users 2 Posts: 570 ✭✭✭


    I am in the process of a big renovation and at the end of it will have a large open plan kitchen and living area measuring 9m by 6m. This room will have 3 large sliding doors.

    One window company I am talking to can do these in Aluclad double glazed with a u-value of 1.6 or in triple glazed with a u-value of 1.2 but at an extra cost of €3k which I can't really afford but I am wondering can I afford not to do it.

    So can anyone out there help me work out if my €3k extra could be paid back in a number of years through reduced heating costs?

    The room is SW facing which I believe is the ideal orientation.


Comments

  • #2
    fatty pang
    Registered Users, Registered Users 2 Posts: 326 ✭✭fatty pang


    Do you really need 3 sliding doors in one room ?
    Non-opening windows will be much cheaper then sliding doors - to buy and to maintain. U-values will also be better
    The u-values you have quoted are pretty poor for both double and triple glazed doors.


  • #3
    galwaytt
    Registered Users, Registered Users 2 Posts: 12,823 ✭✭✭✭galwaytt


    ...put it this way: if you insulate your walls well (to, say 0.21) - then your windows are anywhere 5.7 and 7.6 times worse than the walls you're putting the windows into...............

    Now, if, as you say, the windows form a great % of the area of that room, well then yes, you are going to notice the difference between a 'good' and 'bad' window. The values you're quoting are not great tbh. Considering the size they are, and the amount they will contribute/take away from the performance of the area of the room, I'd have thought you'd have needed to be looking at something much lower - 0.8 or better.

    All imho that is.

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



  • #4
    Jane98
    Registered Users, Registered Users 2 Posts: 570 ✭✭✭Jane98


    galwaytt wrote: »
    ...put it this way: if you insulate your walls well (to, say 0.21) - then your windows are anywhere 5.7 and 7.6 times worse than the walls you're putting the windows into...............

    Now, if, as you say, the windows form a great % of the area of that room, well then yes, you are going to notice the difference between a 'good' and 'bad' window. The values you're quoting are not great tbh. Considering the size they are, and the amount they will contribute/take away from the performance of the area of the room, I'd have thought you'd have needed to be looking at something much lower - 0.8 or better.

    All imho that is.

    Yeah, my windows and sliders have a combined length of 9m in my room which is 9m by 6m so it is a sizeable % of wall.


  • #5
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,146 Mod ✭✭✭✭BryanF


    On a winters day, an overall unit below 1.2wm2k ( when you stand next to the glass) won't feel as uncomfortably cold as the 1.6


  • #6
    galwaytt
    Registered Users, Registered Users 2 Posts: 12,823 ✭✭✭✭galwaytt


    BryanF wrote: »
    On a winters day, an overall unit below 1.2wm2k ( when you stand next to the glass) won't feel as uncomfortably cold as the 1.6

    ..lol:pac:

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



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  • #7
    galwaytt
    Registered Users, Registered Users 2 Posts: 12,823 ✭✭✭✭galwaytt


    Jane98 wrote: »
    Yeah, my windows and sliders have a combined length of 9m in my room which is 9m by 6m so it is a sizeable % of wall.

    30% !! Yikes !

    Ode To The Motorist

    “And my existence, while grotesque and incomprehensible to you, generates funds to the exchequer. You don't want to acknowledge that as truth because, deep down in places you don't talk about at the Green Party, you want me on that road, you need me on that road. We use words like freedom, enjoyment, sport and community. We use these words as the backbone of a life spent instilling those values in our families and loved ones. You use them as a punch line. I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the tax revenue and the very freedom to spend it that I provide, and then questions the manner in which I provide it. I would rather you just said "thank you" and went on your way. Otherwise I suggest you pick up a bus pass and get the ********* ********* off the road” 



  • #8
    Tea 1000
    Registered Users, Registered Users 2 Posts: 4,520 ✭✭✭Tea 1000


    galwaytt wrote: »
    ...put it this way: if you insulate your walls well (to, say 0.21) - then your windows are anywhere 5.7 and 7.6 times worse than the walls you're putting the windows into...............

    Now, if, as you say, the windows form a great % of the area of that room, well then yes, you are going to notice the difference between a 'good' and 'bad' window. The values you're quoting are not great tbh. Considering the size they are, and the amount they will contribute/take away from the performance of the area of the room, I'd have thought you'd have needed to be looking at something much lower - 0.8 or better.

    All imho that is.
    Is any window company honestly getting 0.8 or better? I thought that would be just the glass. The frame is usually the one that ruins a good value.


  • #9
    Superdaddy
    Registered Users, Registered Users 2 Posts: 234 ✭✭Superdaddy


    I'm not aware of anybody getting a u value of 0.7-0.8 from a sliding Aluclad door. The depth of glass required won't fit in a slider frame. You'll get triple glazed but the space between the panes is not wide enough.
    As suggested already you really could reduce cost and increase overall u values if you have just one slider and the rest as fixed glass


  • #10
    Strolling Bones
    Registered Users, Registered Users 2 Posts: 615 ✭✭✭Strolling Bones


    Jane98 wrote: »
    So can anyone out there help me work out if my €3k extra could be paid back in a number of years through reduced heating costs?

    A BER Assesor would be able to tell you this.


  • #11
    rampantbunny
    Registered Users, Registered Users 2 Posts: 907 ✭✭✭rampantbunny


    Tea 1000 wrote: »
    Is any window company honestly getting 0.8 or better? I thought that would be just the glass. The frame is usually the one that ruins a good value.

    Just reading through my docs here...I see a Uw value of 0.72 W/(m2.K) for sliders of 4.6 x 2.6
    Doesn't call out if that's whole window u value but far as I can remember I was told it was.

    Exact text is:
    Triple 54mm coated clear glass
    6btoughened/18Ar/6/18Ar/b6toughened (3FC, 0,5W/m².K, 38dB),
    dB value (EN ISO 717-1): 37 dB,
    Uw value (EN ISO 12567 / EN ISO 10077): 0,72 W/(m².K),


    OP..PM me if you want any info.


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