We are considering replacing our 20 year old upvc windows, they currently have 12mm gap in the glazed units.
We are unsure whether to just replace the steamy units (not all are gone) or go the whole hog and have all new frames with K glass.
Any opinions whether or not there would be a noticeable difference with Pilkington K glass, any thoughts?
Not sure you have the choice any more. Sneaky suspicion that all new sealed units have to have these fancy coated glasses rather than bog standard float glass.
all DG units are now made with this type of glass as standard - one pane (the exterior) has a coating on it, don't worry, there's a sticker telling you which way around it goes!
On Saturday 13 April 2013 20:11 Bob wrote in uk.d-i-y:
You'll need K glass, or one of the other modern coated types, if replacing the window frames to meet Part L requirements. Such glass is the default.
If re-glazing existing frames, you can use what you like (subject to it being toughened if it is in an area that requires it).
Are we likely to benefit from a noticeable heat loss improvement?
One of the windows is a large bay patio window, closing the curtains over the winter has made a huge difference at night.
u values fall a fair bit:
float/air/float 2.9 2.7 2.8 float/argon/float 2.7 2.6 2.6 float/air/Pilkington K Glass 1.9 1.7 1.8 float/argon/Pilkington K Glass 1.6 1.5 1.5
Light levels also fall slightly - so some of that may be offset by slightly longer hours running lighting.
Indeed it will...
I calculated that a 9" airgap and double insulated lined curtains was about a 0.1 U value with a SINGLE glazed 3mm glass window
the curtains 'feel' warmer than the insulated walls.
According to our DG people install it the wrong way round you soon find out if it's on a south facing and sunny side. The unit physically fails...
Does that take into account convection in the 9" gap? Not quite sure if "double insulated lined curtains" is a single pair of curtains with some funny insulation or two pairs of lined curtains one pair by the glass, the gap then the other pair.
Curtains make a huge difference, thick heavy and lined with few gaps, ie drag on the floor or window sill are good. If you have deep reveals, a lined pair next to the window and the thick heavy lined ones over the entire reveal is very good.
I note the quotes around feel. How warm or not something "feels" is fairly dependant on the thermal capacity and thermal conductivity of the material. A big lump of copper at 10 C will feel a lot colder than a 10 C same sized lump of PIR foam.
Are these the u values of each element? So the overall loss is
0.51W/m2 degC?How long before the argon diffuses out through the seals?
AJH
Only if they are in a new frame. like for like in the original frame is permitted AFAICT.
OTOH, it may be harder and more pricy to not use the currently widely available glasses. I've got some to replace and if I just replace the units they will be K glass. I replaced one that had misted up a couple of years ago and it steams up much less than the other units (uncoated) in the frame when the humidity is high.
yes and no, yes because there isn't a deal of convection and no because it doesn't take what there is into account :;)
the curtains we have comprise a fairly thick decorative cotton/synthetic layer, two layers of interlining - essentially a synthetic sort of padding such as you might find in an anorak, and an outer lining that is really there to protect against sunlight.
the three layers hang loosely and mean that convection currents inside the window area do NOT actually have a great deal of effect on the insulation properties of the curtain. the windows all seal well on rubber seals.
that's because the copper has a far higher thermal conductivity and the foam is an insulator. thermal capacity only comes into play after a while. You could put a copper slug inside a lump of foam and it wouldnty make it feel colder as a result until the foam started to draw the heat into that copper.
There is no need to change the frames if they are ok. New glazed units can be made & fitted. You can even take the old glazed units out yourself, take to local window firm & they will make replacements. No problem.
You can get new hinges, catches, draught seals etc too.
The K glass is only slightly more expensive so go for it. You can consider gas filled too but this is quite a bit more expensive and the gas leaks out after a while.
They all leak, the effect is held at bay by a dessicant in the aluminium spacers. (You can see the tiny holes if you look carefully) When used up, they go steamy.
Emissivity.
A 2" gap is just wide enough for convection heat transfer, and as you go wider, heat transfer by convection increases.
I watched our local DG merchant at work assembling a unit. He assiduously poured desiccant into the aluminium spacer sections. The only problem was that it was utterly useless, as he had it in a big open bin under his workspace, so it had already absorbed a load of moisture before he poured it in.
I've no idea how you make sure that these things are done more sensibly.
Not in terms of "feel". It'll be conductivity if you are holding it, as the material is conducting your body heat away, which I think is what Dave was getting at.
That's an interesting question which no one seems to have researched. The EU asked the glazing industry what the loss is, and the industry claimed less than 1% per year which is now in some EU spec, but no one seems to have actually measured it, and I wouldn't be surprised if that's miles out.
Some other research in this area has been on the initial gas fill. It has often been found to be only 75% the claimed gas fill, the remainder being air, and 1 in 10 being less than 70% gas fill. Of course, the claimed performance is based on 100% gas fill.
On the room side our patio door sits in an 8" or so recess, and the curtain rail is fitted above said recess, so there's quite a gap between curtains and patio door.
I got SWMBO to buy some inexpensive curtain lining material, from which she made a pair of curtains to fit the recess. These were hung using an expanding curtain pole we had to hand.
I was expecting the heat loss to be reduced, and the lounge temperature to even out, so I put wireless thermometers in the lounge, between the new curtains and the patio door, and outside the patio door. There result was that the temperature drop across the pair of curtains was greater than that across the patio door, in the ratio of about 60:40, with the outside temperature below freezing.
The great thing is that these secondary curtains can easily be removed when the heating season is over, and the drape of the lounge curtains isn't spoiled by having a lining. £15 well spent...
I assume John missed a header off the table. They would appear to be three different values for the same set-up, I presume for different 'air' gaps.
A U-value is the total of all resistance values, including surface resistances, so U-values can't be added together.
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