Browse Forums Windows & Doors 1 Mar 21, 2010 2:17 pm Hi everyone We have recently purchased a house that is full of floor to ceiling windows and doors. The open plan family/living/meals area is one big window really. They currently all have roller blinds on them. We have not yet experienced a winter in the house, so I have no idea how cold the house may get due to heat loss through all the glass. Does anyone know if these roller blinds are considered 'adequate' coverage to stop too much heat escaping. I really don't want to dress each window in heavy drapes as it will take away from the 'lightness' of the place. (Might consider it in bedrooms but still ???). Anyway, I mainly want to know if anyone knows or has experience with these blinds and if they are enough for the windows over winter?? Thanks, Ceebs Re: Glass windows & doors - question re heat loss 2Mar 21, 2010 3:20 pm The real question is - is your heating system up to the job and can you afford the bill. Roller blinds will moderate the heat loss a little, but not during daytime - assuming you don't want to be in the dark. For every 50 sq.m. of glass and 10 degrees of heating required, you will lose over 3000 watts with single glazing. That can come down to less than half if it's double glazed. Blinds may make 10% difference. Ed "ECOECO" At 'EcoEco', we design windows, we design the best windows, we do it for you, so that when you’re happy we are happy. Tel. 1800 326 326 Re: Glass windows & doors - question re heat loss 3Mar 21, 2010 3:28 pm Ceebs, Heavy drapes are a good solution. You only need to draw them on winter nights. Cheers, Casa Demolition August 2009, Construction Started September 2009, Completed December 2010 Re: Glass windows & doors - question re heat loss 4Mar 21, 2010 8:25 pm There is a tendency for modern home to overglaze but they are a huge source of heat loss and if not properly shades, an excessive source of heat gain in summer. They are the most difficult element of the building to insulate Even the most expensive triple glazing unit loses two and a half times as much heat per square metre as a section of a 90 mm cavity insulated wall. For double glazing 7x, single glazing > 20x. R value insulated wall 3.0 (U value 0.33). The air gap created by an extra pane of glass provides about an additional R value of 0.35 The frame is also a source of heat conduction. Wood or uPVC is better than aluminium. This effect is magnified by lots of small windows. Adding heavy window coverings with pelmets gives R values of up to 0.5. Thin roller blinds probably have negligible insulating value. We considered a 'lighter' appearing option - cellular or honeycomb blinds. They contain air pockets. Their can installed into the reveal to trap a layer of cold still air against the window. Unless your windows are up for replacement then DG will not be cost effective. Re: Glass windows & doors - question re heat loss 5Mar 21, 2010 8:33 pm Our current house has two walls full of windows. We originally had sunscreen blinds, and even with heating it was cold. Not wanting to spoil the "good looks" we added really thick roman blinds which have made a difference. Not a huge one mind you - but much better than just the sunscreen blinds. During the day they lift to the top so we don't lose the effect... My house and my rants.... - viewtopic.php?f=31&t=26937 We are in!!!...and still unpacking. Thankfully there are always Tim Tams Re: Glass windows & doors - question re heat loss 6Mar 22, 2010 7:26 am Yikes.... not sounding too promising then . Thanks for all your posts. Thanks Dymonite and Ed for your more technical responses - I'm not really sure what all the facts and figures mean, but I get the drift (man ). We have ducted heating but I'm not sure how effective this is as we are yet to experience a winter and use it. Yes, was worried about all the glass - it was a stinker in summer (don't know how the previous owners survived without air-conditioning and without awnings or outside screenings - which we need to address for next summer) but now just worried about major heat loss in winter with only having thin roller blinds on the inside. Oh well, will keep all your responses in mind and feel our way through this winter. I don't think we can afford to double-glaze each window (this means actually re-installing ALL the glass doesn't it?? Is there something - like an insulation film - that can be put over existing windows??). Otherwise we will have to look at better 'dressing' options. Just hoping to avoid heavy drapes (and yes, as 'ed' said, you would still lose heat during the day because curtains would be open . Any further input or suggestions much appreciated. Ceebs Re: Glass windows & doors - question re heat loss 7Mar 22, 2010 8:52 am Ceebs Yes, was worried about all the glass - it was a stinker in summer (don't know how the previous owners survived without air-conditioning and without awnings or outside screenings - which we need to address for next summer) Ceebs For radiant heat coming from sunlight entering your home - as you can only change an existing home so much - you need Low-E glass to windows facing the sun. This should stop 80% of the heat coming in... Ceebs now just worried about major heat loss in winter with only having thin roller blinds on the inside. ... I don't think we can afford to double-glaze each window (this means actually re-installing ALL the glass doesn't it?? Generally you can't just install double glazing into existing windows, the windows must be changed. Ceebs Is there something - like an insulation film - that can be put over existing windows??). Otherwise we will have to look at better 'dressing' options. Just hoping to avoid heavy drapes (and yes, as 'ed' said, you would still lose heat during the day because curtains would be open . There are secondary glazing systems which will improve the performance. But they cost about the same as double glazing... as do heavy curtains. Ed "ECOECO" At 'EcoEco', we design windows, we design the best windows, we do it for you, so that when you’re happy we are happy. Tel. 1800 326 326 Re: Glass windows & doors - question re heat loss 8Mar 22, 2010 10:25 am Here's a reason why you should think about double glazing... Front page, last Friday's Border Mail from Albury NSW... Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ "ECOECO" At 'EcoEco', we design windows, we design the best windows, we do it for you, so that when you’re happy we are happy. Tel. 1800 326 326 Re: Glass windows & doors - question re heat loss 9Mar 22, 2010 10:40 am dymonite69 Adding heavy window coverings with pelmets gives R values of up to 0.5. Do you mind sharing your source for this figure? I don't mind being proved wrong, but I'm sure that significantly higher insulation can be acheived with the right mixed of fabrics, layers, design and installation than just 0.5. Re: Glass windows & doors - question re heat loss 10Mar 22, 2010 11:19 am In the commercial range, cellular blinds are quoted as having the best insulating properties around R 0.2 to 0.4. See the Hunter Douglas website. Remember that US imperial R values are about 5.5x the R value that we use. You probably can improve on this by DIY your curtains with foam inserts but the original poster probably wants a more standard look. But let's take this from first principles. Wall/Ceiling insulating thin products like Air Cell, Protherm and E-therm are rated at the most between R 1.0 to 1.5.and they are around 7mm thick. But most curtains are not this thick. Curtains also improve comfort by preventing convection draughts sweeping down the window pane and circulating around the room (in effect wind chill) so the perceived comfort is more than just from the insulation value. Try this experiment, hold an incense stick near the window on a cold night. You will see the plume actually move down with the cold air. This effect is reduced with a window covering. Re: Glass windows & doors - question re heat loss 11Mar 22, 2010 11:27 am Another consideration is: Clear Comfort Film Almost as effective as DG but a whole lot cheaper at $12/m2 versus $300/m2 and DIY! This will preserve your 'look.' Re: Glass windows & doors - question re heat loss 12Mar 22, 2010 11:41 am We have just moved from a cold climate and had glass doors almost the entire lounge/dining area. We set our sentral heating for 16 overnight (most people had it colder, but we wanted it at that temp for the kids). Nights were zero or less during winter. We had roman blinds on all of the doors and a timber venetian on the kitchen window. I would run the heating at about 19 on the coldest days (8 degrees outside) and our gas bills were not too bad. We faced west, so summers were hot. We had ceiling fans installed... We ran our heating just about every day as I was at home with the kids and the winter bills would be about $400 for gas. Hope that puts your mind at ease - window coverings do help... Re: Glass windows & doors - question re heat loss 13Mar 22, 2010 12:53 pm dymonite69, thank you for your explaination - the most useful point being remindered the American R rating being in imperial. I am quite well educated on how to construct window treatments and to improve insulation factors, just lacking putting a figure on it given there are so many factors that can affect a window treatment insulation performance. BTW I have never heard of foam being inserted into a curtain, may increase insulation but will do nothing for the drapability or the looks. Re: Glass windows & doors - question re heat loss 14Mar 23, 2010 10:59 am Thanks everyone - really appreciate each and every response. Dymonite, I will look into that option. Scaredy Cat - that gives me some hope that it won't be tooooo bad. But still, I'd hate to think of all the heat and $$ literally 'going out the door' if we can save some of it. Will see how the onset of winter is. (Curtains would probably look good in winter and help give the place a more cosy feel, but in summer I like the open-ness and brightness - but of course can't have it both ways unless you want to put them up and down each season). Thanks folks..... Ceebs Re: Glass windows & doors - question re heat loss 15Mar 23, 2010 11:33 am Internal window coverings for heat loss. External coverings for heat gain. Re: Glass windows & doors - question re heat loss 16Mar 30, 2010 2:38 pm Hi, I just came across this post. The Mermet range of roller blind fabrics are meant to reduce your energy consumption by 33% (or so it says on their website). They are meant to keep the home cooler in summer and stop heat loss in winter. Not sure how accurate this is... also if it's an exsisting house you bought I suppose you would have no way of figuring out what fabric has been used. I am currently looking to order blinds and looking at going with the Mermet range... not sure if anyone has any experience with their products? Re: Glass windows & doors - question re heat loss 17Mar 30, 2010 7:40 pm Most of the heat gain from summer comes from the direct solar radiation. The best way of reducing this is to block sunlight from entering the house in the first place before it warms up the internal fabric. External blinds, awnings, vegetation and eaves can do this. Shiny or metallic surfaces are more effective than dull, non-metallic ones. Think of light coloured clothing in summer. Heat loss in winter is due to conduction through the building envelope i.e. ceiling, walls, windows. Internal window covering are better for this. The thicker, the better. It is actually the air pockets that stop conducted heat. Think of multiple layers of clothing in winter. The blinds will help a little not they are not the most effective solution. For winter they are too thin and in summer they are on the wrong side of the window. Re: Glass windows & doors - question re heat loss 18Jul 14, 2010 4:34 pm Just wondering if the sunscreen roller blinds are better for insulation than sheer curtains.. Does anyone know? [i]We built in Point Cook and are loving our new house. Re: Glass windows & doors - question re heat loss 19Jul 14, 2010 9:53 pm Heat transfer occurs three ways radiation, conduction and convection. Windows lose significant heat via all three modes. Any physical barrier opaque to electromagnetic radiation will help reduce radiant heat loss. Conductive/Convective heat loss is retarded by introducing a layer of still air next to the window. This cushion of air acts as an insulator. However, if this layer is disturbed it loses its insulating effect. When a cold window is left exposed the air next to it is cooled down by conduction. The cold air begins sinking under convection which draws warmer air from the top. The warm air flows down the surface of the window also cooled forming a continuous convective current. Place a lit incense stick near a window to see this effect. You can also appreciate the sensation of cold air spilling out by placing your hand near the bottom gap of a drawn curtain. DG/TG help keep the air still by sandwiching it between panes of glass. Close fitting curtains with pelmets at the top also reduce this constant flow. Importantly direct your fan heaters or ducts away from the window because they will disturb the still air and accelerate heat loss. Even shutters outside the window will also reduce the movement of cold air moving across the external side of the glass. Re: Glass windows & doors - question re heat loss 20Jul 15, 2010 8:35 am dymonite69 Windows lose significant heat via all three modes. Any physical barrier opaque to electromagnetic radiation will help reduce radiant heat loss. Thanks dymonite69, does this mean that sheer curtains and sunscreen blinds will have the same effect on the cold air? Or is one better than the other in reducing the cold air? Are you also able to comment on the sun damage protection, we have timber floors in the bedrooms and i know that the sunscreen blinds have the UV protection but i really like the look of sheer curtains. Would sheer curtains also offer some protection from sun damage to the timber floors? 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