Is it worth investing in other glass panes? I have now old double glass panes, and it’s not comfortable in the living room. This is what a few clients asked me last month. It took me some research to draw up a conclusion.

History of glass

Have you ever thought about why old houses have normally small windows or leaded glass? When take a closer look at ancient glass, you will see some little bubbles. It’s because of the production process of glass. To make a flat glass piece, first a bubble of glass is blown. It’s cut open en spread on a flat surface. And, this, you could use as a glass pane for your window. Only the rich could afford it, as it was expensive and hard work to make.

Modern glass used for glass panes is float glass. Raw materials are melted in ovens, and the hot glass will float on a tin bath. This makes the glass panels even en without bubbles.

Single glass

Single glass is widely used, until double glass was invented. Nowadays, you can still find it in a lot of houses, especially on the first floor. When it’s cold outside, there will be condensation on the glass on the inside, or even ice. It’s insulates a bit.

Double glass

The double glass pane is made of two glass blades, with a space filled with a gas in between, and some metal strap on the sides to hold everything together. It’s on the market from the 1950s. Since then, there has been a lot of development to improve the insulation. Normal lifespan is 20–30 years. It needs replacement when there is condensation between the glass blades.

HR++ glass

Maybe, you heard that HR++ glass is better than normal double glass. This is true. HR stands for high return. The plus for the improved version.

What’s different between normal double glass and HR++ is that some extra layers of foil are added on the glass, and filled up with argon so that the glass pane will insulate better.

Triple glass (HR+++)

This is a triple-blade glass, with extra foil and gas in between. This type of glass is mostly used in new energy-neutral houses.

How do you know which glass blade are used?

The easiest way is to take a look in between the glass blades. There is an aluminium strip, where there can be a description.

Another way is to use a lighter. Place the flame 5 – 10 cm before the glass. When you see 4 flames in the same colour reflected in the glass, it’s a normal double glass pane. When you see 4 flames, but the second or third is blueish or pinkish, HR++ glass is used.

Is it a good idea to replace the glass?

Recommendable situations

It’s always a good idea to replace the glass when the windows and doors need replacement. In this case, it is also wise to look at how well the new window frames insulate.

Another situation is when there is condensation between the double glass blades. This is a sign that the glass panel doesn’t insulate any more.

The third situation is when you still have single glass panes in your house. Comfort-wise, it will be a huge difference.

How much energy do you approximately save by changing the panes?




In this chart, you can see how much energy you will save, by changing the glass blades.


Mona owns a 1970s house. On the first and second floor, the original single glass panes are placed in the window frames.  She is thinking to replace that with HR++ glass. It’s 10m2.

This will save her approximately 119m3 of gas a year, which is in 2023 €1.45 per m3. That’s €172. The investment would be around € 1700-2000. Check this blog for information about subsidies.

Mona decides that this investment is a good one, especially because she loves to have a warm, comfortable house. And, she is planning to live in the house for many years to come.

It would be another decision when there was already double glass. She would save only 32m3 gas, or approximately €46 a year.


In some cases, it could be a very good decision to replace the glass. Especially, when you have single glass in your window frames, or when there is condensation between the glass blades. Renewing the window frames would be a good moment to update the double glass panes too.

Are you thinking of improving the energy efficiency of your house? Save time and energy by planning a kickstart. We will draw up a plan together, specified for your situation. So, you know where to start and what would be a good investment. For more information, click here.


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