Browse Forums Eco Living 1 Oct 08, 2010 1:35 pm I am planning to have double glazed windows on my house. My question is: what is low E glass and what does it do? Do you have both double glazed and low e glass together or are they separate products? Percentage wise what is the difference in price to a normal window? Would you put it on all windows even the south facing? SOrry, but these terms really get to me and I'm not quite understanding the details. Cheers, Carolyn Re: Low E Glass 2Oct 09, 2010 12:14 pm Low E glass means low emissivity, so it allows solar energy through but reflects radiant heat from inside back in. Ie, it is great for winter heat loss prevention. You can have low e double glazing or normal double glazing. Typically Single pane glass has a u-value of 4.7 (without frame) double glazing is 3.0 low e is 2.2 So it is quite good. But only if your problem is winter heat loss. If your problem is primarily summer heat gain then maybe not worth it. South windows recieve very little radiant heat gain but potentially can lose heat from artificial heating. So from a passive design not so important, but with mechanical heating potentially beneficial. James Re: Low E Glass 3Oct 09, 2010 2:07 pm jamesd Low E glass means low emissivity, so it allows solar energy through but reflects radiant heat from inside back in. Ie, it is great for winter heat loss prevention. You can have low e double glazing or normal double glazing. Typically Single pane glass has a u-value of 4.7 (without frame) double glazing is 3.0 low e is 2.2 So it is quite good. But only if your problem is winter heat loss. If your problem is primarily summer heat gain then maybe not worth it. South windows recieve very little radiant heat gain but potentially can lose heat from artificial heating. So from a passive design not so important, but with mechanical heating potentially beneficial. James Actually its benefit is exactly the opposite... it works very well stopping around 80% of radiant heat (solar heat gain) from sunlight entering windows, but has next to no benefit in retaining heat, the vast majority of which is lost through conduction, only double glazing will help there. The u value is meaningless and can't be compared to the u value for double glazing as it measures a different method of heat transfer. Couple double glazing with Low-E for the best of both worlds, but use low-E on its own and you may get thermal stress causing cracking - and it's a devil to clean. Don't use it in single glazing, only use it where windows face North or West. Adds about $60-$100/m2 compared to double glazing alone. 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: Low E Glass 5Oct 09, 2010 10:25 pm Yes, a lot of people choose to put low-e on the north side, and we also have recommended low-e glass in our windows because of its energy saving properties. However, one of our customers recently used computer simulation in an environmental assessment to model the way the sun will cast shadows on to the house and decided to put low-e only on the west side. In this case, it was calculated that there was not enough heat gain during winter and it was desired to utilize glass with a higher SHGC (Solar Heat Gain Co-efficient) in north facing windows to permit solar heat gain from the low winter sun. Low-e is a coating, so if you have double glazing you can use it on either side! For instance, during winter when you have a high inside room temperature, compared to the cold outside, a non low-e coated glass surface will absorb radiant heat and then re-radiate it towards the cold exterior; while low-e coated glass with the coating towards the room, will absorb less and reflect most of the radiant heat back to the interior, thereby reducing the overall heat loss. At the same time, other customers had it on all the windows, irrespective of their location - they wanted to use the same glass because they were concerned that it would appear a slightly different colour. Sydney Double (and now Triple) Glazed Windows and Doors mob 0412 717 066 Sydney, Canberra, Newcastle, Wollongong www.doubleglazedwindows.net.au Re: Low E Glass 6Oct 20, 2010 12:30 pm Hi Windowfactory I am an energy rater who at times specifies Low E Glass, however I am having quite a bit of negative feedback from developers who have heard about problems with low E glass cracking along with the known cleaning problems. Have you had heard of low E glass being more prone to cracking? I just cant understand why this would be so as it is just a film. Regards Nathan Re: Low E Glass 7Oct 20, 2010 12:57 pm Nathan Peart Hi Windowfactory I am an energy rater who at times specifies Low E Glass, however I am having quite a bit of negative feedback from developers who have heard about problems with low E glass cracking along with the known cleaning problems. Have you had heard of low E glass being more prone to cracking? I just cant understand why this would be so as it is just a film. Regards Nathan Hi Nathan, I have written about this in other threads. Low-E is not a film, it's a metallic coating. The problem with Low-E is that in a laminated form when the building internal and external temperatures are vastly different, it causes thermal stresses which cause one layer of the glass to crack. Low-E is only really successful in double glazed units, where it is usually not laminated and is also not subject to the thermal stresses. Added to that, Low-E does not perform the same function as double glazing, so although the u-values are comparable in energy rating software, they don't work the same. The u-value for Low-E refers to its affect upon radiant heat, whereas the u-value for double glazing refers to conducted heat. In cool climates (heating required), the only real value is in double glazing. 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: Low E Glass 8Oct 20, 2010 1:14 pm My house has double glazing and low-e. This is a great combinations. As others have said, single glazed low-e is possible, but just go the extra step and get low-e double glazing. The low-e coating goes on one of the inside faces. If on the face closest to the inside of the house, you retain winter warth (very handy at night). If it on the face closest to the outside of the house you can reflect summer heat. I've gone for the retaining winter heat option. So, if at all possible go double glazed low-e and you'll have the best cost effective windows. (Just make sure your air gap is at least 12 mm.) Demolition August 2009, Construction Started September 2009, Completed December 2010 Re: Low E Glass 9Oct 20, 2010 1:40 pm Thanks for the calrification Ed, I now see where the problem ******. Over here in the west Double Glazing is very rarely used due to the perceived high cost. Nathan Re: Low E Glass 10Oct 20, 2010 2:11 pm Nathan Peart Thanks for the calrification Ed, I now see where the problem ******. Over here in the west Double Glazing is very rarely used due to the perceived high cost. Nathan Welcome... if I had a distributor there prices would tumble... know anyone doing windows right now who might like to do work with us? 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: Low E Glass 11Oct 29, 2010 1:00 pm Sorry Nathan been flat out didn't check till now. Lucky Ed stepped in to explain. If you (or the developers) are very concerned about low-e cracking than try toughened glass - less likely to crack than coloured low-e or other forms of low-e . Toughened glass is a form of safety glass, and you can get low-e toughened. It will be more expensive, but at the same with the right marketing they can capitalize on this eg retirement villages, family-friendly, daycare centers etc, so even when there is no legal obligation to use safety glass they will consider upgrading. Cheers Sydney Double (and now Triple) Glazed Windows and Doors mob 0412 717 066 Sydney, Canberra, Newcastle, Wollongong www.doubleglazedwindows.net.au Thermal Modeling 12Dec 23, 2010 2:05 pm I'm doing thermal modeling for homes and the program that I use, (I believe all programs are following the standard NatHERS terminology so they must be similar) gives me a far more better SHGC improvement for toned windows than low e windows. Here are the numbers; a single glazed clear window SHGC 0.74 a single glazed clear window SHGC 0.63 a single glazed tinted window SHGC 0.49 a single glazed heavy tinted window SHGC 0.28 Tinting is what I use to get out of situations when a window is overheating a zone rather than low e glazing most of the times. Shading is also an excellent option and a smartly angeled element can block summer sun while letting the winter sun in since the sun is higher in summer than in winter. In my opinion only selecting double glazing or low e glass is not a very informed approach. A particular U value and SHGC value is what determines the final performance of a glazing element and those numbers can come from a variety of combinations in glazing and frame types. Also each window must be analysed in its own context so a low SHGC for a window may not necessarily be beneficial toward the overall comfort of the room. Manuel Basiri Re: Low E Glass 13Dec 23, 2010 2:55 pm Does anyone have any experience with Sunergy glass? 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