Single vs double glazed windows

[GrahamHowie]

Your original posts says you currently have slimline double glazing.
So assume doing nothing is an option for you? Or have I miss understood your post.

yes, I have that currently but some panes failed, along with my neighbours who used the same supplier. It helps when more than one pane fails, kind of makes it clear what next steps are.

Yep, I'm going to start replacing my failed double glaze slim line with vacuum slim line. I think vacuum is naturally slim line.

But before that window task can progress I've a water leak to find - damp pathes appearing in frontage stone wall. FUN!

 

[leyasg]

Not sure we have any professional window or thermal designers here. But maybe.

Can I ask why you want to switch from slimline to vacuum glazing?
Sounds like a great expense for little gain.

Performance is 1 W/m2k better with vacuum (which is quite impressive).

If in winter we assume average of 5 degrees outside, and 20 degrees inside. That's a DT of 25.
So reduction in heatloss is 25W per m2 of window.

If we assume a four month period where it really matters, then that's 72kwh per m2 per year.
Gas and oil are around 6p per kwh. For a modern boiler let's assume 7p output.

£5 per year per m2 of window upgraded.

Work out your payback period. Anything over 25 years if a waste of money as vacuum panes do fail. If you are paying more than £125 per m2 I really wouldn't bother. I have no idea what replacing the glazing to vacuum costs.

That's really interesting. I don't know the m2 of windows, but I'd be surprised if it were more than say 100m2 (and that would be over egging it I am pretty sure). That would mean £500 additional heating cost, on a £50k bill - 1% return so definitely not worth it. And you would be able to reduce the heat loss (and cost) further by putting decent heavy curtains.

The question is what happens when it's -5 outside (as has happened this week). Does the house stay warm enough inside? If it does, then this whole exercise is a pointless waste of time and money. There are some windows we need to get changed anyway, and I was thinking of getting them double glazed when we are doing them rather than single - the cost difference isn't significant.

PS - I've never had anyone do this calculation before. Sceptic in me is questioning whether it is correct? I have no reason to doubt you, and as someone after you has already said, they think the cost might be lower still. If correct, the whole (window/door/EPC/eco?) industry should be reprimanded for encouraging/forcing replacement to double glazed. It would suggest a significant money making scheme with some trade union or window company pushing the narrative, nothing more. As the benefit is so slim, and the accountant in me would do a cost benefit analysis to find it a big waste.

 

[montyjohn]

PS - I've never had anyone do this calculation before. Sceptic in me is questioning whether it is correct? I have no reason to doubt you, and as someone after you has already said, they think the cost might be lower still. If correct, the whole (window/door/EPC/eco?) industry should be reprimanded for encouraging/forcing replacement to double glazed. It would suggest a significant money making scheme with some trade union or window company pushing the narrative, nothing more. As the benefit is so slim, and the accountant in me would do a cost benefit analysis to find it a big waste.

This has come up recently here before.
From a purely economics point double glazing doesn't make any sense (unless you need new windows anyway).

To justify it you would need to add value to security, future maintenance. Can't remember the other counter arguments now.

The other thing my calculation assumes is that the old windows are well maintained and are not draughty.

The question is what happens when it's -5 outside

So this is the other argument. If your heating system is undersized such that it can't heat your house, then it's more likely to be more economical to upgrade insulation instead of upgrading the heating system. A new boiler is silly money, however, larger radiators plus the ongoing extra running cost needs to be factored in.
But you would need to know if upgrading windows will allow your room to meet 20 degrees when it's -5 outside.
So you still need to do the heat loss calculation.

I would suggest working out all the payback periods for all forms of insulation upgrades and just start with the low hanging fruit.

 

[leyasg]

This has come up recently here before.
From a purely economics point double glazing doesn't make any sense (unless you need new windows anyway).

To justify it you would need to add value to security, future maintenance. Can't remember the other counter arguments now.

The other thing my calculation assumes is that the old windows are well maintained and are not draughty.



So this is the other argument. If your heating system is undersized such that it can't heat your house, then it's more likely to be more economical to upgrade insulation instead of upgrading the heating system. A new boiler is silly money, however, larger radiators plus the ongoing extra running cost needs to be factored in.
But you would need to know if upgrading windows will allow your room to meet 20 degrees when it's -5 outside.
So you still need to do the heat loss calculation.

I would suggest working out all the payback periods for all forms of insulation upgrades and just start with the low hanging fruit.

Thanks. Lowest hanging fruit is just sealing the gaps in the existing window frames. Any advice on how to do this best temporarily (until summer)? Wood filler or the putty?

 

[Cubist]

Thanks. Lowest hanging fruit is just sealing the gaps in the existing window frames. Any advice on how to do this best temporarily (until summer)? Wood filler or the putty?

Wood fillers and putty will dry, crack and lose their ability to prevent water ingress. PlumbersMait from the likes of Screwfix is your best short term option. It's typically used for sanitary ware joints. It never sets and provides an excellent temporary seal around window frames and can easily be removed when you do the times comes for permanent repairs.