Low-emissivity glass for single glazing?

[fernicarry]

Pilkington claim that this reduces the heat loss through the glass by 75%.

Question is can you use low-e glass for single glazing? Or is the coating too fragile and therefore it has to be on the inside of a DG unit to protect it?

 

[a twig]

Original low e coatings were a bit fragile but things have improved now and current gen like LoE i89 or similar proprietary coatings are fine and available on single glazed panes - Pilkington and other manufacturers sell them now.

Obviously it is more effective when employed in double or triple glazed units but no reason not to use it as far as I can see

 

[fernicarry]

Thanks. Seems like a cunning way of decreasing heat loss without having to resort to chunky DG. Cost might be prohibitive and of course won't be reflected in EPC rating.

 

[paulc]

Pilkington claim that this reduces the heat loss through the glass by 75%.

Up to 75% saving. If one were to go from single glazed (u-value 5.8 W/m²K) to standard double glazed (1.6 W/m²K), you'd get a substantial saving straight away. Go for triple glazed vacuum units, you could get as low as 0.7 W/m²K - Current building regs for replacement windows mandates a u-value of 1.6 W/m²K, and low E glass is pretty much standard so that you can hit that target.
Installing low E glass in a single glazed window might get you down to 4.0 W/m²K, but that is well short of the 75% claim - In conjunction with secondary glazing, you could possibly get under 2.0 W/m²K.. With the price of energy going up all the time, any saving that can be had must be a good thing as long as the cost is less than the savings. But then the improvement of comfort is something that isn't so easy to put a value on. I've spent way too much money on thermal improvements here (new windows, wall/loft insulation), and it is going to take a very long time to claw back that money through energy savings. But it has made a huge difference to my quality of life (no more cold draughts or getting up in the morning to a freezing house).

 

[fernicarry]

Up to 75% saving. If one were to go from single glazed (u-value 5.8 W/m²K) to standard double glazed (1.6 W/m²K), you'd get a substantial saving straight away. Go for triple glazed vacuum units, you could get as low as 0.7 W/m²K - Current building regs for replacement windows mandates a u-value of 1.6 W/m²K, and low E glass is pretty much standard so that you can hit that target.
Installing low E glass in a single glazed window might get you down to 4.0 W/m²K, but that is well short of the 75% claim - In conjunction with secondary glazing, you could possibly get under 2.0 W/m²K.. With the price of energy going up all the time, any saving that can be had must be a good thing as long as the cost is less than the savings. But then the improvement of comfort is something that isn't so easy to put a value on. I've spent way too much money on thermal improvements here (new windows, wall/loft insulation), and it is going to take a very long time to claw back that money through energy savings. But it has made a huge difference to my quality of life (no more cold draughts or getting up in the morning to a freezing house).

Thanks for the numbers. Agree completely on comfort. We've gone from the heating being on 24x7 and making no apparent difference to the internal temperature to it still being on quite a lot of the time but at least can get above 19' most days if we choose. But once combustion boilers are eventually banned we could be back where we started unless I can further reduce the heat input required.

My thinking is to avoid the chunky appearance of standard DG and/or the cost of conservation DG whilst still making a useful improvement. Lets see what that looks like:

Say my living room window area is 5m2, inside temp is 20, outside is 0 (but we only get a handful of days this low). 100W heat loss per unit u-value (assuming I've interpreted the units correctly?).

Current state, standard SG at 5.8, heat loss is 580W. Heat input into this zone is about 6kW with boiler cranked up to 11. [Historic Scotland quote loss through windows in a solid stone building at 20%, where is the other 10%? Drafts around the sashes, reveals, weight boxes?]

With low-e SG the loss could be 400W a saving of 180W. Doubtful whether that's even noticeable in comfort or money terms. So much for that idea...

With full fat 3G the loss would only be 70W saving 510W.... getting somewhere as as fraction of the heat input so might be worth a few hundred pounds a year. You might even break even over the working life of the units. But changes the appearance of the window openings quite dramatically. Crosses my red line.

Somewhere in the middle is heritage DG at around 1.5 u-value (Histoglass HD12) loss of 150W, saving of 430W. Also useful. Install cost likely to be substantial so could only be justified on a comfort and aesthetic basis. Issues with weight (need to increase the size of counter weights to keep pulleys), noticeable change in appearance (to the very picky). Realistically probably the best option and importantly one that the EPC box-ticker can understand if we need to reach the holy grail of a C to avoid the wrath of the Green Lobby.

Histoglass also do SG units with u-value of 1.9 which can be made with traditional cylinder glass, presumably with an eye-watering price tag... Some of my top sashes still have cylinder glass in them, but the value of that to me is knowing that the glass is 160 years old not just that it looks a bit funky.

The future is bleak IMO but I will battle on chipping away at small improvements and maybe someone will appreciate them sufficiently to buy this White Elephant off of me.

Meanwhile, I'll be under the floor attempting to fit a breather membrane and a bit of insulation. At least the mice will be happy...

 

[paulc]

The future is bleak IMO but I will battle on chipping away at small improvements and maybe someone will appreciate them sufficiently to buy this White Elephant off of me.

Chipping away at it is about the best many of us can do. Given enough money, I could get this place up to a C, perhaps even a B, and have the work done in a matter of months. Instead, it will probably take me another five years, and by that time, goal posts will have moved yet again.

P.S. Nothing wrong with your maths

 

[88v8]

Histoglass also do SG units with u-value of 1.9 which can be made with traditional cylinder glass, presumably with an eye-watering price tag... Some of my top sashes still have cylinder glass in them, but the value of that to me is knowing that the glass is 160 years old not just that it looks a bit funky.

I have Histoglass units, 6mm. Hand-made glass. Yes, it is expensive, but one only does it once.
The glass has a lovely wave to it. From inside and out, it does not shout Sealed Unit!!!
They were front-puttied with Kawo Elastokitt (alternatives are available) so they are indistinguishable from single-glazing unless one is very near.
Do not use bead glazing. It looks crass and the units will fail.

They do not eliminate misting, but the windows no longer run with water.
No idea of the u value.

I was fitting new casement windows so I had the rebates made a bit deeper. Existing sashes could be routed out, as you say the weights would need to be a bit heavier. I did that in our previous house where I fitted 1" units, what with the units and the hardwood sashes I had to cast my own lead weights. Those units were float glass and you could tell a mile off that they were sealed units, but 40 years ago one culd not get sealed units with hand-made glass.

For me, in a period property, the appearance comes first. If one's priority is energy efficiency, one has bought the wrong house.