Window insulation

[Stinsy]

Not a drop of condensation on the inside at all. Funnily enough the outside pane gets so cold the warm morning air often condenses on the outside!

The actual glass panes themselves have an exceedingly low U value often better than the wall! However it is the frames that are the weak point, UPVC (that I have) just cannot keep up with the glass. You need thermally broken aluminium frames if you want good insulation for the whole unit. But while these look fantastic, they're not cheap!

[marshman]

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[Joeboy]

A wee update, 9 degs outdoors. We are seeing 18.6 degs on the triangular insets and 17.1 dregs on the unadorned rectangle.

Happy with that and more importantly it has not triggered SWMBO's style parameters. I may yet live thru Winter!

GCH is kicking in for 30 minutes at 06.45 hrs both zones and for 10 mins upper zone only in the evening. All these wee 1 to 1.5 deg improvements (there have been many) that are ongoing & the Woodstove are making a huge difference to our fossil fuel use. Hoping we can get into start Dec as we are and that will be a massive win over FF in previous years.

Edit- continued the thinning process for solar gain and log harvesting.

[GarethC]

You need thermally broken aluminium frames if you want good insulation for the whole unit. But while these look fantastic, they're not cheap!

You mean they can be better than UPVC frames? Given aluminium's a better heat conductor than UPVC, that surprises me. What do you mean by thermally broken?

[Stinsy]

You need thermally broken aluminium frames if you want good insulation for the whole unit. But while these look fantastic, they're not cheap!

You mean they can be better than UPVC frames? Given aluminium's a better heat conductor than UPVC, that surprises me. What do you mean by thermally broken?

UPVC cannot meet modern insulation standards. Obviously aluminium itself conducts heat extremely well (ever tried to weld aluminium?), but at the same time some of the best-insulated windows are "aluminium framed". The "thermally broken" bit is the important part. Ie the bit of aluminium on the inside isn't the same piece of metal as the bit of aluminium on the outside.

Interestingly hardwood frames are making a comeback. These can meet modern insulation standards, but while they look fantastic, they require maintenance.

[Oldgreybeard]

Not a drop of condensation on the inside at all. Funnily enough the outside pane gets so cold the warm morning air often condenses on the outside!

The actual glass panes themselves have an exceedingly low U value often better than the wall! However it is the frames that are the weak point, UPVC (that I have) just cannot keep up with the glass. You need thermally broken aluminium frames if you want good insulation for the whole unit. But while these look fantastic, they're not cheap!

We get this a lot at this time of the year. This morning there was a thick layer of frost on the outside of the windows, but the inner pane was sitting at 18 deg C at the inside surface. It's noticeable that more heat leaks out through the frames than the glass, even though we have passive house windows, with a thermally broken aluminium/foamed PVC/timber construction. This shows up by there being no ice within about 50mm of the edge of each frame.

Our glazing is pretty good though, 52mm thick triple glazed units, with a centre pane U value of 0.38 W/m².K. The overall U value for each window is a lot worse though, because of the frame conduction, even with warm edge spacers and 20mm cavities between panes. Most of the glazing comes out at between 0.6 W/m².K and 0.8 W/m².K, with the biggest windows being better than the smaller ones.

[nowty]

[Our glazing is pretty good though, 52mm thick triple glazed units, with a centre pane U value of 0.38 W/m².K. The overall U value for each window is a lot worse though, because of the frame conduction, even with warm edge spacers and 20mm cavities between panes. Most of the glazing comes out at between 0.6 W/m².K and 0.8 W/m².K, with the biggest windows being better than the smaller ones.

That is pretty good, the triple glazed units I have are only 40mm thick and fit into standard frames with a slightly shallower angled beading. In fact if my units were filled with air they would be worse than the standard 28mm thick double glazed units but the argon makes a big difference.

28mm Double glazing has one 20mm gap with two panes of 4mm glass.
40mm Triple glazing has two 14mm gaps with three panes of 4mm glass.

Krypton can be used instead of argon to improve the U value further but its circa 1000 times the price of argon so is rarely used.

[Adokforme]

Not a drop of condensation on the inside at all. Funnily enough the outside pane gets so cold the warm morning air often condenses on the outside!

The actual glass panes themselves have an exceedingly low U value often better than the wall! However it is the frames that are the weak point, UPVC (that I have) just cannot keep up with the glass. You need thermally broken aluminium frames if you want good insulation for the whole unit. But while these look fantastic, they're not cheap!

Thanks Stinsy and Roger there's certainly food for thought there, so appreciate your observations. Hadn't considered the weight aspect so a useful piece of info to tuck away.
If aluminium frames can boast a thermal break to give better performance then cannot plastic frames be designed similarly? Unless of course rigidity of the material comes into play!
Something else I've discovered is that our windows were only installed in 2014, we purchased the property in '16, naturally replacement cost is a factor but it's more the thought of ripping something out and replacing before it's past it's best. Then again, perhaps it's best was never good enough!
I guess that's for me and my conscience to wrestle with. Any further thoughts!

[Stinsy]

Any further thoughts!

If you’ve got really decent A-rated, Argon-filled, double glazing, then I’d leave it. If you’re changing the windows anyway the small extra cost of triple is worth IMO. And if you have crappy, out-dated, air-filled or blown, double then it is worth changing them for triple.

Not just about the energy savings, cold windows cause currents of cold air to make the room uncomfortable even if it is warm.

[Adokforme]

Thanks Stinsy, checking back on the paperwork it would appear our windows are rated A+, according to BFRC standard. Couldn't find whether this included Argon gas, although suspect not.There is an A++ rating also. Reckon we'll hold fire on replacing until one of the glazing units blows or fails otherwise. The bathroom is north facing so might be the favourite to test out initially, although it has had a Seasonal double glazing film applied(from a well known DIY store) and for a couple of years now does seem to be very effective. It's not cold to the touch and seldom gets covered in condensation!
Thanks again for a pragmatic view. Makes sense to me.