Double glazing, HR glass, triple glass and vacuum glass

Single glazing, double glazing, HR++ and triple glazing... what does it actually mean? The word says it all: single glazing consists of 1 layer of glass and does not insulate, double glazing consists of 2 layers and insulates moderately. HR++ is double glazing with a coating and an insulating gas between the plates, which makes it insulate very well. Triple glass consists of 3 panes of glass with a coating and insulating gas, which makes it extremely well insulating. A somewhat unknown type of glass is vacuum glass: it is double glazing that insulates extremely well. This type of glass is more expensive than HR++ or triple glass.

Costs and savings HR++ glass

Are the frames still good? Then HR++ glass in the existing window frames is a good choice. If you replace all windows (22 m2) in an average corner house with HR++ glass, it will cost approximately € 4,000. After deduction of subsidy, approximately € 3,000 remains.

And what do you save with it? Suppose you had double glazing everywhere, you would save about 70 m3 of gas annually. This saves about €100 per year in energy costs at a gas price of €1.45 (the average gas price for 2025-2040). Exactly how much you will save depends on what gas price you pay. Did you still have single glazing everywhere? Then you even save 260 m3 of gas per year (which amounts to € 370).

Below you will find an overview of the costs and savings if you install HR++ glass throughout the house (in existing window frames). Do you want to know what triple glazing costs and saves?

Costs of HR++ glass in existing window frames

Type of home	Cost	Subsidy	You pay net
Terraced house	€ 3.800	€ 900	€ 2.900
Corner house	€ 4.000	€ 1.000	€ 3.000
2 under 1 roof	€ 4.500	€ 1.100	€ 3.400
Detached house	€ 6.000	€ 1.400	€ 4.600

Savings: replacing double glazing with HR++ glass

In the table you can see what you will save if you have double glazing throughout the house and have it replaced with HR++ glass.

Type of home	Gas savings per year (m3)	Savings per year at gas price 1.45 euros/m3
Terraced house	65 m3	90 euro
Corner house	70 m3	100 euro
2 under 1 roof	80 m3	110 euro
Detached house	100 m3	140 euro

And if you replace single glazing?

If you replace single glazing, the costs remain the same, but the savings are a lot higher. Below you can see what you will save if you have single glazing throughout the house and replace it with HR++ glass.

Smart spending of your money

You will immediately notice the benefits of insulating glass: your house stays warmer and you feel less cold and draught. If you still had single glazing, you also get rid of foggy windows and water on the windowsill. But what about the financial benefits? You pay the costs in one go, but you will see the savings on your energy bill every year. So attractive in the long term.

The profit you make if you replace single glazing with HR++ glass is comparable to an interest of 6 percent on your savings account. The current interest rate on a savings account is around 3 percent. And don't forget: it is also good for the value of your home and the climate.

Subsidies and loans for insulating glass

Insulation costs money. How do you pay the costs? There are attractive subsidies and loans for insulation and other sustainable measures.

• There is a national subsidy for insulation. The subsidy is a fixed amount per square meter. If you have 2 or more measures carried out, you have an additional advantage: the amount per square meter is then twice as high.
• The subsidy for triple glazing is higher than for HR++ glass, but then you must have it installed in a new insulating frame. But because of the subsidy there is almost no price difference with HR++ glass in existing window frames.
• Some municipalities and provinces also provide subsidies for insulation.
• Are you going to take out a mortgage? You can borrow extra money for energy-saving measures.
• There is also an advantageous loan for energy-saving measures.

Check: what kind of glass do you have?

In order to insulate your windows in a smart way, you first need to know what kind of glass is in them. That determines how much you can save and whether it is worth replacing the glass.

How do you know what kind of glass is in your windows?

You probably recognize single glazing: it consists of one pane of glass. You can clearly see this where the glass is in the frame. With double glazing you will see an aluminum strip between the plates on the side, near the frame. But how do you know whether it is simply double glazing or HR glass? A few simple tricks and tips to check:

• Hold a lighter or a lit match 5 to 10 cm in front of the window and look at the reflection of the flames in the window. You see 4 flames. Are all flames the same color? Then you simply have double glazing. Does the second or third flame have a different color (usually pink or blue)? Then it is HR glass. The different color is caused by the coating of the glass. With this trick you can only see whether you have HR glass, not which type of HR glass.
• Check whether there is a code on the aluminum strip between the glass plates with HR, HR+ or HR++. If nothing is listed, there is a good chance that you simply have double glazing.

Replacing single or double glazing?

Always replace single glass
Do you still have single-glazed windows? That is not isolating and is no longer contemporary. We therefore recommend that you immediately replace all single glazing in your home with HR++ glass or triple glazing. Not only will you save a lot of energy, you will also have a more pleasant home: it stays warmer and you hear less noise from outside. You can also opt for vacuum glass, but that is a lot more expensive.
Are you hesitating between regular double glazing and HR++ glass? Don't: you won't save money by opting for regular double glazing. New window frames with regular double glazing are just as expensive as with HR++ glass.

Do I also need to replace single glass in:

• unheated rooms? Yes, even in rooms that you do not heat, it is worthwhile to replace single glazing. Your house loses a lot of heat through these rooms, especially if they are adjacent to rooms that you heat.

• the conservatory? Not if you have an unheated conservatory that consists largely of glass, which you can close off from the rest of the house and which is located on the sunny side of the house. Due to the large glass surface, it is better to install single glazing in the conservatory. Otherwise the temperature will be too high in summer. Do install HR++ glass in the windows and doors between the house and the conservatory. If you heat the conservatory, it is smart to replace the single glass.

Simply replace double glazing in heated rooms

Do you now have 'normal' double glazing, without one or more advantages? It makes sense to replace it with HR++ or triple glazing in rooms that you regularly heat, such as the living room, kitchen and an office that you use a lot. This provides more comfort and saves energy. In unheated spaces, it is only financially worthwhile to replace double glazing if you are going to renew the window frames. You can also opt for vacuum glass, but that is a lot more expensive.

Regular double glazing is also called thermopane glass.

Only replace glass: choose HR++
Are your window frames still good? Then you basically only have to replace the glass. Choose the glass with the highest insulation value. For existing window frames this is HR++ glass. Triple glazing insulates slightly better, but you also have to replace your window frames. A lower insulation value than HR++ is a shame, because you save much more energy than with 'normal' (old-fashioned) double glazing. You don't have to worry about the costs: HR++ glass is just as expensive as old-fashioned double glazing.

There is also vacuum glass, which is double glazing that insulates very well. It is a lot more expensive than HR++ glass, but can be a good solution in monuments or narrow window frames, for example.

Check your window frames

But it's not just about the insulation value. Also check whether your current window frames are suitable for thicker (and therefore heavier) types of glass, such as HR++ glass. Wooden frames that are still in good condition can usually be adjusted by milling out the rebates and using glazing beads.

The advice is therefore as follows:

• Choose HR++ glass if it fits your current window frames. If necessary (and possible), have the rebates milled out and glazing beads installed.
• Sometimes HR++ glass does not fit in the rotating parts of your window, because they are a bit thinner. Then use HR++ glass in the places where it is possible (in the fixed part of the window) and HR+ or HR glass in the places where HR++ glass does not fit (in the rotating part of the window). Milieu Centraal advises to limit the use of HR+ and HR-glass as much as possible, because it insulates less well than HR++ glass. And you don't get a subsidy for it. Instead of opting for less good glass, you can also replace the frame of the window that can be opened. You can then have HR++ glass installed in that frame.
• Doesn't HR++ glass fit anywhere? Then you can still consider replacing the window frames in heated rooms. Especially if you think that the window frames will need to be replaced within 10 years or because you want to make the house energy neutral. That seems very expensive, but the subsidy for triple glazing in new insulating frames is quite high: this can largely cover the extra costs for insulating frames. Please note the conditions for the subsidy: for example, you must also insulate your floor, roof or exterior walls to receive the subsidy, or get a heat pump.

No wooden frames?

Are your window frames made of material other than wood, for example steel, plastic or aluminum? Then get advice about the possibilities. For example, some houses have steel frames that are too characteristic to replace.

In general, double glazing in plastic or aluminum frames can be replaced by HR+ or HR++ glass. Is that not possible or will your window frames need to be replaced within 10 years? Then replace the frames with new insulating frames, preferably with triple glazing.

Replacing glass tips:

1. Please note: if you install thicker (= heavier) glass in a revolving window, you often have to replace the hinges, because the window becomes much heavier (especially if it previously had single glazing).
2. If you combine triple glazing with other types of glass, pay attention to differences in color and light. For example, if you install triple glazing in a large window frame and HR++ glass in a smaller window next to it (that can be opened). Ask the glass company to show you the difference in advance. HR++ glass can easily be combined with other types of glass.
3. Replacing glass or window frames is not a big job. You can have your entire house fitted with new glass and window frames in 5 working days. And it creates little mess in the house: you only have to move some furniture and clean it afterwards.

New window frames? Triple glass!

Do your window frames also need to be replaced within the next 10 years? Then choose triple glazing with new insulating frames and double gap seals. This gives you the best insulation for your windows in one fell swoop. And the additional costs are not too bad: insulating frames with triple glazing are about 7.5 percent more expensive than regular frames with HR++ glass. But because the subsidy on triple glazing in new window frames is almost 3 times as high as that on HR++ glass, you ultimately pay about the same for it.

Costs and savings triple glazing

Below we have calculated for 4 types of homes what triple glazing in insulating frames costs and how much you save.

Vacuum glass: super good insulating

Vacuum glass is a special type of double glazing that insulates just as well as triple glazing, but is much thinner. The pane is approximately 8 mm thick: that is thinner than all other insulating glass. Vacuum glass is a lot more expensive than HR++ glass or triple glass. It is an alternative to monument glass for monuments or protected cityscapes.

Questions about vacuum glass

A different approach: additional window, foil or monumental glass

Is HR++ or triple glazing not possible in your home? You can also improve the insulation value of single glazing in other ways: with additional windows, window film and monumental glass. The savings and the feeling of warmth are comparable to 'normal' double glazing. Milieu Centraal only recommends these forms of insulation if HR++ glass is really not possible for your home. For example, if you live in a monument or a rental house.

Additional window or window film

With an additional window you can easily create 'double glazing' from existing single glazing. The additional window is placed on the inside or outside against an existing wooden frame or in a steel frame, so that an insulating air layer (air cavity) is created between the glass plates. Additional windows are also available with HR coating: they insulate better than additional windows without coating.

Are you short on money or are you looking for a temporary solution until you can tackle it more thoroughly? Then frame foil can be a solution. It gives the same result as an additional window, but is cheaper. A disadvantage is that it is more likely to be damaged.

Monument? Special glass or window film

There is special insulating glass for monumental buildings: monumental glass. This looks like old glass and is quite thin so that it can be placed in existing window frames. There is single and double monumental glass.

There are also alternatives to monument glass. One alternative is vacuum glass. This type of glass is thin but insulates very well and can look like old glass. This makes it suitable for monuments. It is more expensive than monumental glass, but you also save more. And you can get an ISDE subsidy for it (you don't get this for monumental glass). A cheaper alternative is insulating window film. And with insulating curtains you can keep the heat in even better in the evening and at night.

Small panes of glass or stained glass?

Does your window consist of small panes with slats in between? Then consider replacing it with one large window with a window division in the cavity (i.e. between the glass plates) or on the window (this is called Wienersprossen). You can hardly see the difference, even though it is cheaper and insulates better than all the separate small panes of insulating glass. It is also possible to place stained glass in the insulating glass (this will then be placed between the glass plates).

Please note: ventilation, insulation, temperature and 'leakage'

Glass types: single, double, HR, triple and vacuum glass

There are all kinds of insulating glass and their insulation value varies considerably. They are listed in the table below.

U-value = insulation value

The insulation value of glass is expressed in a U-value. The lower the U-value, the better the glass insulates. Triple glazing in a new frame has a U-value of 0.4 to 0.9. Single glazing has a U-value of 5.8. So remember: with glass you aim for the lowest possible U-value.

The table below shows the annual gas savings per square meter of window per type of insulating glass. This concerns the average savings in heated and unheated spaces. In heated areas the savings will be higher, in unheated areas lower. The savings have been calculated for the entire window, that is: the insulating glass plus the frame in which the glass is located.

Type of glass (U-value)	Annual gas savings per square meter of window
Vacuum glass (0.4 – 0.7) in existing frame	13,7 m3
Triple glazing (0.4 - 0.9) in new insulating frame	12,2 m3
HR++ glass (1.0 - 1.2) in existing frame	11,9 m3
Double glazing (2.7)	8,7 m3
Single glass (5.8)	does not apply

HR++ glass is available with 2 or 3 glass plates. With 2 panes of glass we often call it HR++ glass for short, with 3 panes of glass we often call it triple glass.

Insulating frame: U-value 1.3 or lower
Standard frame: U-value 2.4

What is HR glass?

HR glass is an abbreviation of high-efficiency glass. HR glass consists of 2 or 3 panes of glass with a space in between (the cavity). With HR and HR+ glass there is normal dry air between the glass plates. With HR++ and triple glass there is a noble gas between the glass plates (usually argon). The air or noble gases in the cavity provide the insulation. Noble gases insulate better than dry air.

All types of HR glass also have an invisible coating (layer) on the glass plate on the room side, which improves the insulation even more. Hence the designation HR: high efficiency. The coatings reflect heat while allowing light to pass through.

The more pluses, the higher the insulation value

Every time experts develop and market new glass, the insulation value increases. First came HR glass (high efficiency glass). When this was improved, pluses emerged: after HR came HR+ and HR++. HR++ glass has a coating and there is noble gas between the glass plates.

HR++ glass was initially only available with 2 glass plates, but recently also with 3 glass plates. With 2 panes of glass, it is officially called HR++ double glazing, but in practice it is usually simply called HR++ glass. HR++ glass with 3 glass panes is officially called HR++ triple glass, but this is usually simply called triple (or tripel) glass. Other words for triple glazing are: triple glazing, triple glazing or HR+++ glass (with 3 plus signs). In general, the more pluses, the higher the insulation value.

More important than the names is the U-value of the glass: the lower the U-value, the better the insulation. Triple glazing has a U-value of 0.4 to 0.7, HR++ (double) glazing from 1.0 to 1.2.

Sun-resistant HR glass

There is also sun-resistant high-efficiency glass: ZHR++ double or triple glazing. This is HR glass with an extra sun protection coating on the outside glass plate. Sun protection glass lets in less sunlight and is cooler in the summer, but in the winter you benefit less from the sun than with HR++ glass. It is therefore better to choose HR++ glass with sun protection on the outside of your house than ZHR++ glass. This way you can better retain the heat of the sun in the summer and use it better in the winter. ZHR++ double glazing is especially useful in places where outdoor sun protection is difficult to apply, such as in high-rise buildings. It is not recommended in ordinary homes.

Insulating glass and the environment

Insulating glass is good for the climate: you use less energy and therefore fewer greenhouse gases are released into the air. In an average corner house you can save about 260 m3 of gas per year if you replace all the single glazing with HR++ glass.

Of course, the production of HR++ glass also requires energy. But with HR++ glass you save so much energy in your home over the years that this more than makes up for the production energy. The noble gases (such as argon) and coatings in triple glass and HR++ glass are harmless to health and the environment.

Insulating glass when it is very warm outside

During the heating season, insulation helps to keep the heat inside. And during hot days, insulation keeps the heat out. An insulated house then stays nice and cool for longer. But has it warmed up inside? Then it is more difficult to lose the heat than in a non-insulated house. You keep the heat inside.

Solar radiation through your windows further warms your home. With single glazing, a lot of solar heat comes in, but at the same time a lot of heat goes out. HR++ glass has a reflective layer that ensures that solar radiation can enter and that the heat of the home also remains inside. This is a big advantage in winter, because it warms up even faster inside. If you want to keep the heat out, it is a disadvantage: it will ultimately be warmer with HR++ glass than with single glazing.

Fortunately, in many cases you can prevent it from becoming very warm inside by placing sun blinds outside. Think of sun cloths and awnings. This way, the sun's rays cannot pass through the glass. Indoor sun protection such as curtains is less effective than outdoor sun protection, because the solar radiation has already passed through your glass and is in your house. Exterior sun protection is always important, but if you have HR++ glass, it is even more important.

Old glass to the glass trade

The window glass of your windows is not allowed in the bottle bank. Hand it in at the glass store or the recycling center in your municipality. The glass is reused for the production of new glass (especially packaging glass). This saves energy and raw materials.

Quality marks and guarantees

Ask for glass with the KIWA or KOMO quality mark: you can be sure that it is what it says it is. Between the glass plates or on a sticker it is stated whether it is HR, HR+ or HR++ glass. The sticker also indicates the inside and outside of the glass for correct installation.