When existing or new home owners think comfort and energy efficiency from their windows “Double glazing” comes to mind, right!
Double glazing is definitely much better than thin 3mm glass that’s common in existing windows. For new buildings glass and frames have to meet modern energy ratings so double glazing is used with modern type frames.
One factor that is not really explained to customers wanting double glazing is what is its thermal performance like and how does it compare to alternatives? It’s almost as confusing as trying to compare mobile phone plans and we’ve all been there before!
How is double glazing performance rated?
For new windows the glass and the frame is rated as a whole. But if we just want to really know about the glass itself, particularly if we want to change the glass and keep the frames or let’s say we need new windows but we really want the best glass available, what’s the story about the glass itself?
These subjects are always a bit complicated and we will try to simplify it for you, with a focus just on glass efficiency and with particular emphasis on double glazing.
As an example. When we buy a new vehicle one key consideration (apart from looks, safety, functionality and price) is how much fuel does it use – in other words, what is the fuel efficiency? Let’s face it, fuel is becoming expensive and fuel efficiency is important for running costs as well as environmental implications.
So we’ve been conditioned over the years to ask about and consider fuel efficiency as a natural part of our purchasing decision. Recently emission ratings have also been applied to new vehicles. But it’s pretty fair to say we don’t necessarily think the same about double glazing for new windows or retrofitted double glazing to existing windows. And when you go to seek the basics it’s a mine field to understand or make an informed decision.
One reason for that is it’s a commonly held belief that double glazing is all the same. Well it’s not. Beware that what seems cheap/affordable double glazing is not necessary good performing or long life double glazing.
Do we actually understand how double glazing performance is rated in efficiency terms?
A key ingredient to consider for thermal efficiency of glass is the U-value. The U-value measures how much energy escapes through the glass panel per m2. U-value measures the capacity of thermal loss for heating/cooling, similar if you like to how effective roof/ceiling bats are rated for insulation properties.
The U-value is a key number to focus on for the performance of the glass. The higher the U-value the less efficient or the worse the glass is. You should aim for the lowest U-value possible and take into account the longevity of the glass/double glazing.
Below is a diagram which explains the different thermal efficiency of ordinary thin glass, e-coated thing glass and a range of conventional rubber sealed double glazed units and the new vacuum insulated double glazed unit, Glavenir, made by Panasonic.
So from the above U-values it’s clear that thin old glass is the least efficient. E-coated glass is only 38% better than thin glass and a common retrofit double glazing used in Australia is only 44% better than old thin glass. As the conventional double glazing gets thicker and argon gas is used there can be up to a 75% improvement. But the down side is these thick sections will not retrofit into existing frames and they have other issues including moisture ingress and gas escaping as well as unsightly looks.
It’s also clear that all double glazing is not the same in performance. This is what you should take on board when comparing prices. Ask one simple question of your potential supplier:
“What is the U-Value of the glass”? And for new windows also ask “What is the combined U-value of the glass and frames”?
You may just get a shock that all the money you are spending is not actually getting the best results, because all double glazing is not the same. Spend a bit more and get peace of mind for quality and best comfort and energy efficiency.
The best performing double glazing is vacuum insulated double glazing at 90% better than thin glass. It’s in fact as good as and better than some triple glazing. It’s only 6.1 mm or 8.1 mm thick depending on what your requirements are with U-values of 0.9-0.58 respectively. This amazing glass fits existing window frames and the technology is proven to last in excess of 50+ years because unlike conventional double glazing there is no rubber seal to be broken down by moisture (a common failing over time of rubber sealed double glazed units).
So in a nutshell
- U-value is a key measurement for thermal performance of glass, especially double glazing
- U-value changes based on the technology used
- Double glazing varies for the U-value based on space between glass, type of glass used and if air or argon is used as a gas in the gap or instead if it’s a vacuum (the best insulator of all)
- If you’re spending money retrofitting existing windows with better glass or considering new windows, ask what the U-value of the glass panels alone are and the new glass with new frames.
- Cheap double glazing is not necessarily good double glazing
- For just a little bit more expense you could have triple glazed thermal standard which will last a very long time (50+ years) and give you the ultimate energy efficiency and comfort as well as help conserve energy.
- Try to resist accepting that all double glazing is the same in performance when you are quoted a price – it’s not.
- Compare U-values and you can be confident about longevity of your purchase and ultimate value of money.
Click here to find more out about Glavenir Vacuum Insulated Double Glazing
