Glass quality and replacement windows

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An acquaintance has asked me to put a question to the hive mind on his behalf.


He has an old house in Bath in which he is planning to replace the windows thies year. He intends to replace like for like on the aluminium frames but is unsure of the pros and cons of the various glass types and brands available, for example, is Saint Gobain glass better than Pilkington, etc.


Ideally, he would like some solar shading but without an obvious tint as this woukd look too different next to the windows that aren't being replaced.


I will get some more detailed information tomorrow as to his objectives.


Thanks, all.

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What type of windows? Are they original? How old is the house?


Alu frames are relatively recent, and in this country mainly post war. Looking forward to the detail.


I think in the US they go back to about 1930 .. around the time of the Empire State Building.


There is a company Called the Heritage Window Company who may advise .. but that is not a recommendation, just a note.


Or a body called the Historic Houses Association, but if they are Alu and original I do not think it is likely to their territory, as the house will be relatively recent.



Edited by Ferdinand

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Giving this a little bump as my acquaintance has come back with a very detailed summary of his query regarding the properties of different products for his replacement windows.


Hello Vivien
Thanks for your, and others (the "hive mind"), interest and assistance. I hope that I can summarise the context and our objectives sufficiently succinctly. Our house started off as a low-efficiency 1950s concrete block cavity wall ('reconstructed' Bath stone) horror, with Crittall windows, but over the past 30 years we have increased the energy efficiency considerably. So each small improvement does make a noticeable difference.

Back in the late 1980s we installed thermal-break aluminium double-glazing from Smart Systems, using a Bristol installer. The windows were fairly cutting edge at the time, with 28mm glazing, and the fairly narrow aluminium section kept the look of the original Crittall windows fairly well. Smart Systems have grown over the years and we used their current windows when we altered our kitchen 5 years ago. Now, as the 30 year old windows are in generally poor condition, we plan to replace all the other windows with Smart Systems current Alitherm 300 system, with 28mm argon-filled DG units. The question then arises as to whether we should go a step beyond standard DG units, at least in some of the windows?

Our primary and possibly sole objective is to improve insulation, as we are replacing relatively large windows in both our dining room and lounge. A secondary objective, if achievable, would be to reduce solar gain in our front-facing bedrooms, which catch the full afternoon and evening sun during the summer and can reach around 27 degrees C during the evening. However we do not want glass which is, or appears to be, tinted or reflective compared with standard glass. Our proposed window installer is currently suggesting that we use "Planitherm" glass (from Saint-Gobain, for additional insulation in the dining room and lounge windows, and we have not yet discussed the bedrooms.

Attached is a photo of the west-facing corner of the house taken at 3.50pm today (equivalent to 2.50pm in the summer), and the sun can clearly be seen shining onto both the south-west and north-west side and front elevations. It is perhaps surprising how much sun in fact falls on the front north-west facing elevation even at this time of the year, and during the summer it has sun from around 2pm until sunset. The large window in the photo is the main dining room window, 2.45m wide by 1.8m tall, the sliding doors on the right of the dining room will be replaced by fixed windows as we never use the doors, and the front-facing end of the lounge can be seen to the left of the photo. The main bedroom window is above the main window of the dining room.

I'd be very interested to hear if anyone has any experience of or comments about Planitherm 'Energy Standard' or similar products, which I assume are coated on the inward facing face of the inner pane to reflect heat back into the rooms. Do they noticeably decrease heat loss? Is, for example, the benefit of using a glass which is coated to retain heat within the rooms negated or outweighed by the solar gain within sun-facing rooms on sunny summer days? We could perhaps use Planitherm in just the lounge windows, as one end is rear-facing anyway and the front-facing end (in the photo) is the least affected by summer sun. And do any of these products look tinted or reflective, not least because we regularly have birds fly into our windows and any additional reflection of the surroundings would presumably make this worse.

We would be very grateful for any feedback.




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