Seal windows: save heat and energy properly

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Seal windows: This keeps the cold out and the heat in

Self-adhesive rubber seals are a cheap solution for wooden windows

© dlewis33 / Getty Images

When it gets colder outside, the heating season starts in many households. But despite the artificially generated heat, there can be a draft in some rooms, especially near the window. Then at the latest you should get to the bottom of the matter in order to save energy and avoid mould.

So-called drafts are promoted by leaks that occur exactly where different materials meet – for example at the window. Because wooden frames in particular work all year round (they expand when it’s hot and contract when it’s cold), there are small gaps between the seals and the natural building material. And it is precisely through these that the cold air can get unhindered from outside into the interior of the apartment, which in turn means that the radiators have to generate even more heat. This is not only noticeable in the energy costs, but also in the frame: the damp air makes it easy for mold. You can avoid both in good time if you seal your windows. You can find out what you need to consider here.

Draft test: How to unmask leaky windows

You can use a trick to find out whether a window is leaking: close all the doors and then light a candle (a lighter can also be used). Run them along the inside of the window frame. If this starts to flicker, you have discovered a leak. If you don’t feel comfortable with the fiery experiment, you can also use a sheet of paper: place it on a corner of the (open) frame and close the window again. If you can pull the blade out easily, you can assume that there is a leak. Especially if you tighten the screws with an appropriate tool and still get the same test result. Then it’s time to seal the windows.

Which materials are suitable for sealing?

There are now a variety of different materials that are suitable for window sealing. Self-adhesive sealing tapes made of foam, rubber seals, silicone or acrylic as well as window putty have proven particularly useful. But what are the differences between the various options and what are the advantages and disadvantages? An attempt at an explanation follows:

Rubber or foam sealing strips
The self-adhesive tapes can be ordered in different colors and shapes (width and length are variable) and can also be cut to size afterwards, i.e. shortened. They are particularly suitable for window frames made of wood or metal to seal leaks. The advantage of sealing tapes is clearly the low price, but they hold up rubber seals significantly longer (depending on the manufacturer up to eight years) than foam seals, which only offer a short-lived problem solution of one to a maximum of two years. Installation is easy with both.

To find out how wide the seals need to be, you should measure the frames in advance. The best way to determine the gap size is to wrap ordinary play dough in cling film (you can also use felt or paper) and then place it between the frame and the sash – and briefly close the window. If you choose rubber sealing strips, you can choose between E-profiles for narrow joints and P-profiles for wide joints. Self-adhesive sealing tapes made of foam are also available in different sizes and colors (Black and White) available.

If your windows are made of plastic and already have prefabricated rubber seals, no more may be glued over them!

silicone and acrylic
The difference between these two sealing options is also in the details: While their consistencies are quite similar, window silicone or Grout Silicone a rather shiny and acrylic sealant a more matte texture. The first material is water-repellent and elastic, while the second can easily be painted over – which is particularly important for wooden windows if they have to be repainted, for example. However, if you want to seal the windows in the bathroom, silicone is for the sanitary area the better choice – because it does not let water through, even in damp rooms.

window putty
The adhesive and sealant based on linseed oil was used decades ago – and is still suitable today for wooden windows that were sealed with the material. Because although window putty waterproof and eco-friendly, it doesn’t last very long. For this reason, leaks have to be repaired from time to time. To do this, the old putty only has to be heated, for example with a hair dryer, removed from the joints and refilled. The material is as elastic as play dough and can easily be molded into the desired shape. It then takes a few days to dry.

In the fall, the windows should be checked

If you seal your windows properly, you can save on heating costs in the long term

© macida / Getty Images

Seal windows: These are the most important steps

While sealing windows is certainly not rocket science, the following tips can help achieve a clean result:

  1. Before you get to work, you should clean the window frames and the joints. Light dirt can be removed with water and detergent, for stubborn spots you can use alcohol, for example.

  2. The old seals and adhesive residues must then be removed. A spatula can be very useful here to remove the residue. You can also oil any wooden fittings.

  3. If you want to seal your windows with silicone, you can press some cling film or paper onto the material and wet it with soapy water. After that, close the wing to allow the silicone to dry.

  4. Rubber seals are suitable for plastic windows: depending on the width of the gap, these should be between 1 and 3.5 millimeters thick. When attaching, it is important that the tapes are tight at the corners.

  5. When you’re finished caulking the window, you can use the draft test above to make sure you’ve sealed any leaks and haven’t missed any gaps.

And one last tip: Ideally, you not only seal your windows from the inside, but also from the outside – because there can also be weak points through which cold air can get inside the apartment. However, finding the leaks is a lot more difficult, so it’s best to focus on the obvious crevices.

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