Double Glazed Windows - How to Calculate ROI?

goingDHfast on 03/03/2017 - 07:30

Hi All,

We are building a new house in Melbourne and having trouble deciding if double glazed windows are worth investing in. For the purpose of our exercise we are trying to set aside any emotional positions (ie; its better for the environment/eco friendly) and look at this purely from a practical cost effeciency point of view.

Has anyone done this sort of maths already for a new home that already needs to meet 6 star energy ratings? We may only put double glazed windows in the living area of the house which is three large windows and somewhere in the range of $6-8,000 more (have to do it through the builder).

For a house which already has 6 star energy ratings (without double glazing), surely it would take 10+ years to pay back $6-8,000 in heating/cooling savings? We would have zoned refrigerative cooling and gas ducted heating FYI and the living area is around 40 square metres.

Cheers,
gDHf

Home & Garden

Comments

  • mskeggs on 03/03/2017 - 07:38
    +2

    Don't know the maths on double glazing, but can you advise why you are using gas rather than reverse cycle aircon?
    The running costs tipped well into AC's favour a few years ago, I understand, and as you are spending the money to install it for cooling, and presumably will have solar panels as well, gas seems an odd choice.

  • donbot on 03/03/2017 - 07:46
    +2

    Heating/Cooling is one factor. Noise is another. Double glazed will be a LOT quieter.

    I would love to upgrade all my windows in my apartment to be double glazed to knock out some of the noise in the area around me… but havent investigated if this is realistic to achieve without replacing the entire window frame.

    • blackmanshade on 03/03/2017 - 15:06

      I believe secondary glazing is far more effective in acoustic performance than your typical double glazed windows. You may want to look into that option for your apartment as its also cheaper and may not need to go through strata for 'approval.'

      • OzFrugie on 03/03/2017 - 19:18
        +1

        I am interested in this. Can you link me to recommended providers? How much are they?

        • 191919 on 11/03/2017 - 18:32

          how did you guys go with this? in a similar situation. dogs on all 3 sides of me really ruining enjoyment of my bedroom ;(

    • dbun1 on 04/03/2017 - 22:06

      Your typical double glazing only helps a little bit as the spacing between panels is too small for effective noise reduction.

      What you want is a secondary panel so you can achieve approx. 100mm between panes.

      • OzFrugie on 05/03/2017 - 22:31

        Can it be installed on existing window frame? I am in an apartment so most likely have to use existing frame otherwise strata wont be happy

  • pao2x on 03/03/2017 - 08:10
    +1

    Say it saves $100 a quarter in energy it would take a long time to recoup that amount. However it doesn't really depreciate that much

  • Hipmumma on 03/03/2017 - 08:26

    I was looking into this and decided that it was much too expensive. Another option was to get installed reflective tint which I didn't due to not being able to see outside at night properly.

    In the end I picked up some very good quality curtains secondhand for $300 (they would be around $500 each to get new I'd say). They have the Velvet fabric and another curtain behind which is purely for thermal protection. They do a great job and keep the house cool for most of the day for days under 40 degrees. In the kids rooms I've put blinds up with their coloured curtains.

    It's important to look at the way your house faces as well. All the bedroom windows face east and I find they are the coolest. West facing windows make the rooms heat up quickly. I have my garage, laundry and bathroom on this side so minimal use /windows keeps the house cool. It's amazing the difference this has made to the house.

    If your at work most of the day or don't mind a darker house the curtains/blinds are a cheaper alternative.

    If your expecting To live in the house for many years or live in a loud area with trains going past at night for example it may be worth doing glazed windows

    • [Deactivated] on 03/03/2017 - 08:37

      I have tints. You can see outside from inside very clearly. People from outside cant see whats inside your house. Its pretty good.

      • Hipmumma on 03/03/2017 - 14:14

        Oh really that's great! I went to a tint place and they said at night it can be difficult to see outside when it's dark so I didn't get them installed

        • [Deactivated] on 03/03/2017 - 17:46

          Nope I see fine outside. I dont have the darkest tints so that helps. I definitely recommending tinting. I only have it at the front. I am planning to get it done to all the windows.

      • kryptoz on 03/03/2017 - 22:35
        +2

        @Shiv86:
        The technical principle with tints is that light passes through it from the light side to the darker side, but in transmission, the percentage of tinting blocks the amount of light passing through it.
        * Day-time: a 20% tint would allow 80% of the light to pass into a car/house; Then, assuming no light sources inside, only a fraction (eg. 50% of 80% = 40%) of the daylight will be reflected (by walls/furniture/curtains/etc), the tint will only let 80% of 20% = 16% of the light coming back outside. The same principle applies to what you can see — if there is a person inside, you won't be able to see them very well in this example with only 16% of their image visible.
        * Night-time: if there are no nearby streetlights, but there are lights on inside the house, the situation reverses — 80% of the light/image could be seen outside from the street, but a person inside will see very little of what is outside.

        Reflective / Mirror tinting is entirely different, it uses a metallic finish on the outside layer, which reflects a large proportion of light, on the inside face these films are typically black; they reduce admitted light by around 80% meaning the rooms inside will be very dark even in full sun they are also not visually attractive; but have the benefit of full privacy at all times.

    • OzFrugie on 03/03/2017 - 20:54

      Which curtains do u get? My place is facing west and its so hot in the summer although i have tinted windows..not reflective one though due to strata issue

      • Hipmumma on 03/03/2017 - 21:32

        It might not be too stylish but one of the better fabrics is actually velvet. I picked up a set that uses Laura Ashley fabric. The second curtain is a thermal white/creamy thick fabric. Another option is to buy a quality three block out blind as well as thick curtains with thermal backing. You could get both of these at spotlight when on sale.
        Another option for the really hot days if you don't mind about looks temporarily is something my friend did…she put up those windscreen covers you use for your car on hot days on the inside of her window and she said it works really well lol

        • Hipmumma on 03/03/2017 - 21:33

          Oh also Velvet is commonly used in home theatre rooms etc too because they help block out noise

  • supaderp on 03/03/2017 - 08:27
    +1

    Google "solar gain calculation through windows/ glazing" this is usually the (glass U-value x temp. difference x surface area of glass), but you must also account for the location and angle of the sunlight throughout different time of the days. Anyways, once you have the solar gain value, do the same calculation for the double glazed windows. Results will be in watts.

    Reduction in solar gain (W) = (solar gain_double glazed) - (solar gain_existing windows), this is not to be confused with the input power reduction.

    Reduction in input power (W) = Reduction in solar gain (W) / EER, you can find your EER and COP on the back or side of your air
    conditioning unit. Usually EER is around 3-4 for modern systems.

    $$ saved = Reduction in input power (W) * electricity rate

    • supaderp on 03/03/2017 - 08:31

      Oh don't forget if you have an outdoor awning, then this affects your calculation slightly.

  • Hipmumma on 03/03/2017 - 08:27

    Oh and also don't forget to upgrade your insulation in the roof and walls

  • supnigs super skids on 03/03/2017 - 08:38

    How much is sound proofing worth to you?

    • goingDHfast on 03/03/2017 - 16:37

      Not much to be honest, we're in a very quiet area already.

  • jason101 on 03/03/2017 - 08:45
    +2

    Checkout Veridian smart glass it has excellent thermal properties and only slightly dearer than regular glass.

    • OzFrugie on 03/03/2017 - 21:06
      +1

      Do you know how much it costs? It doesnt have sound insulation property does it?

    • jhmtaylor on 04/03/2017 - 11:47
      +1

      I agree with this. I did a major renovation on our house about three years ago which included replacing all external doors and windows with E glass. It added about $3000 to a $32,000 glass bill, installed. We estimated The difference was approximately 4 degrees celsius warmer in winter and the same cooler on a very hot day in summer. The only reason I would choose double glazing over E glass would be noise reductiom.

      • OzFrugie on 04/03/2017 - 18:15

        Which e-glass did you get installed? Viridian smart glass?
        Which supplier/installer did you use?

        • jason101 on 04/03/2017 - 21:23
          +1

          We've just moved into our new house before Christmas, 1/2 the windows are smart glass (low e) and half aren't, the difference is amazing especially those low e windows which are tinted glass as well (we have a western facing laundry with a sliding door instead of a door/window in the room, I'd go as far as saying even in full sun the room is comparable to other non full wall window rooms on the same side of the house.

          If I'd known how good it was I would have just got the whole house done. Given it's literally just the glass I think retrofitting existing windows is probably worthwhile for windows which get direct sun even in older homes.

          In respect of noise I don't think there is a difference but thicker glass (also available as low e) does make a huge difference, I work for a builder and our high end apartment stock uses much thicker glass (required by regulation due to building height) the difference in sound insulation is amazing.

          If you google the veridian product they have a neat little video about their product, their stockists are also listed. In SA the company I work for uses A&L Windows and Packers who both can supply the product. I'd assume any glazier can get it.

  • sane on 03/03/2017 - 08:56
    +3

    The problem is not if double glazing makes sense. The problem is that the builders massively overcharge for double glazing. Frankly, putting in double glazing when building, it should be little more than the base cost. However, they see it as a profit line.

    I'd be inclined to haggle hard on the price.

    Saying that, it makes a great deal of difference to noise etc., it's not just the heating & cooling. So think about where the noise sources will be, and where you will too. What cost blocking out a barking dog?

    Oh, and in the UK double glazing is getting supplanted by triple glazing for only a little more (and it's much better at noise). There you can get an entire 4 bed house retrofitted with triple glazing for ~$10000

    • Hipmumma on 03/03/2017 - 21:34
      +1

      I have actually read somewhere that it can actually be cheaper to get the house built then replace the windows with double glazing afterwards

      • sane on 03/03/2017 - 21:52

        In Australia, very probably.

        The manpower should be the largest component of the cost, and if they are putting in the units from new, the cost delta should be small (relative to having to rip out the old and install new).

        However, as most find, builders are conmen and are looking for ways to start from a low base price and inflate it beyond recognition - and double glazing is one way they do that.

        State government should have mandated double glazing as a standard years ago. You'd probably find that when building from new, the RoI against solar panels would be better (provided you don't allow for inflated pricing).

  • JimB on 03/03/2017 - 10:03
    +4

    ROI will be difficult to calculate, but double glazing will be more comfortable.

    I'm building myself and will be sourcing my own windows.

    I will definitely be double glazing all windows, didn't even bother with single glazing quotes.

    What you should also note is that double glazed window frames are usually much higher quality than single glazed window frames.

    If you have West Facing windows and are going double glazed, get low-E glass.

    • jason101 on 04/03/2017 - 21:28

      +1 for frame thickness / quality makes a massive difference in double glazing in terms of acoustic performance.

  • blackmanshade on 03/03/2017 - 15:13
    +3

    You might want to have a browse on these links efficientglazing WERS.

    • kryptoz on 03/03/2017 - 23:13
      +1

      Agreed. Double-glazing often does not give a great benefit, depending on climate zone, orientation and shading over windows; In short double-glazing helps more with heat loss (U), not so much with solar gain (SHGC) where the type of frames or the coating/film can have a much bigger benefit. Ideally, you would choose a triple-glazed system with coatings on each layer in a thermally broken frame, but they are likely to be prohibitively costly, especially if you have a lot of glazing in the house.

      Also note — when building a home you will get a NatHERS certificate which states your house is 6+ stars — the sad truth is that many builders will often substitute the specified items, particularly high-rated windows/doors, for inferior ones for a fraction of the price that aren't certified nor meet any Star Rating/U/SHGC; some builders will also put less than required insulation in; (Unlike overseas, there is no performance testing done post-construction (either by building surveyors or Australian government agencies to compare what was built matches what was designed, and certified by the energy rater).
      This costs yourself (and the environment) a lot in energy costs and thermal comfort, but it profits the builder substantially. The only way to protect your investment is to ensure the windows delivered and installed on site match the brand and model of those on the WERS.net website (esp. U/SHGC requirements).

      • goingDHfast on 04/03/2017 - 07:53

        Great info, Cheers. We're hiring an independent building inspector so hopefully he's on the ball with checking these things. I will definitely check out wers.net too.

  • boccos on 04/03/2017 - 08:36

    Though not solving your issue, I live in the tropics and have had the onerous job of trying to reduce the heat entering a west facing room from the afternoon sun. Tried window tinting and that was a total failure. Eventualy the best way was an external awning that stopped the sunlight hitting the window glass directly. Massive difference in room temperature. Goal achieved.

  • [Deactivated] on 04/03/2017 - 21:38
    +1

    Double glazed (or more correctly, double paned) windows is not necessarily much better for thermal insulation.

    Firstly, as many mentioned, it greatly reduced noise. My office is fully double pane as 90% of the exterior walls are glass. Would be incredibly noisy if it was single paned.

    But if you are looking at traditional sized windows, it will depend on how much direct sunlight you're getting. At full afternoon direct sun, double pane doesn't do much to prevent heating up and is hinderence if you are planning to film tint internally). The film reflects some heat but the heat now travels through the air pocket twice, greatly heating up the air insulation layer between the two panes, which partially diffuses back into your house. In a shaded area, it's great as the ambient heat is insulated by the air pocket.

    As for heating cost, double pane always helps but depends greatly on how much warmer than outside ambient temp and how well the rest of your walls are insulated. Warm air rises, so if your ceiling is average, most of your heating runs out there.

    • goingDHfast on 05/03/2017 - 07:49

      This is really useful info, Cheers. One of the areas we are considering double glazing for is the alfresco which is shaded for most of the day. It's a set of five stacking tall glass panel roller doors so not cheap but it may indeed be the most effective heat reducing area according to the points you listed. Luckily we've been able to almost eliminate west facing windows in our design (view is to the north).

      • [Deactivated] on 05/03/2017 - 10:54

        Glad it helped.

        Another potential design is a folding french door. Tend to have better seals around the seams and opens completely.

        Sliders with internal compartment to open completely have a large poorly sealed hollow that leaks air.

  • Adz81 on 04/03/2017 - 22:43

    3M has some window films (or tints) which are simply brilliant in their heat reduction… I've seen these demonstrated in a mining camp and the room temperature was greatly reduced… They're not cheap, but I'll be using them when I build.

    • kryptoz on 05/03/2017 - 00:27

      I'm sure you would find they are much 'cheaper' than say LowE glazing, where the film is bonded to the glass during manufacturing. The effectiveness may be equal, especially with 3M's ceramic films, but in the longer-term the films will bubble and split, even if they are professionally installed — you are unlikely to ever have that issue with LowE or other similar glazing.

  • snook on 06/03/2017 - 12:41
    +1

    The best way to stop heat coming in is an outside awning. You want the heat to not hit the window in the first place.

    We are replacing all our windows with european style double glazed. They are absolutely fantastic.

    We bought them from here: https://master-haus.squarespace.com/
    but no longer know how their business is going. Service at the time was fantastic.

    With existing windows, we got smaller windows and cut them into the existing frames, OR built them up around the install. Love them.

    • goingDHfast on 06/03/2017 - 12:46

      Interesting, cheers. I have a large north facing picture window. In winter it will let a huge amount of natural light into our living area (and also help to heat the room). Would it make sense to double glaze a large north facing picture window given the fact that in summer the sun is overhead anyway and in winter we want light and heat to enter the room?

      • snook on 06/03/2017 - 12:59
        +1

        Depends on you really. You know how Australian houses are. Our house is early 1900's and the glass was thin in the sash windows. Some windows had been changed to aluminium with two layers of glass on top of each other (i call this australian double glazing).

        You only had to go near these windows in winter to feel the cold and draft coming in. The issues with both styles in our house was to do with age and/or the install - gaps everywhere etc.

        If you went with aussie double glazed and a proper install with good sealing, I reckon that would do you on that particular window. The double glass layer didn't do much of anything for the heat/cold but was better than a single layer. Newer windows would also have thicker/better glass to start with. As people are saying about curtains, this is true also - thick curtains with insulation backing AND a pelmet (must have the pelmet) would work for you if the glass you already have is ok.

        We also live on a really busy road and the windows have added luxurious dampening to the sound.

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