The paper sheet test: find out yourself where the air enters

Do you feel a cold draught near the window even when it is closed? Do you hear whistling when the wind blows? Before calling a specialist or changing anything, you can find out yourself, in two minutes, exactly where the air is coming in — with a simple sheet of paper. It is the simplest airtightness test, used even by professional installers, and it costs nothing. This guide shows you step by step how to do it and how to interpret the result.

Why the paper test works

An airtight window presses the gasket evenly all around the contour, so that no gap remains between the sash (the moving part) and the frame (the fixed part). If somewhere the gasket no longer presses — because it is worn, because the hardware has loosened or because the window has dropped slightly over time — a micro-gap remains there. Cold air enters through it and, in wind, the whistling occurs.

The sheet of paper measures precisely this clamping force. Where the gasket presses correctly, the paper is held firmly and you cannot pull it. Where the pressing is weak, the paper slides out easily — a sign that there is an air leak at that point.

> The basic idea: if the paper comes out easily, the air comes in easily. The test shows you on a map, point by point, where the problem is — information a specialist would otherwise find using this very same test.

What you need

Just an ordinary sheet of paper (A4 format, printer paper). You do not need tools, apps or devices. Optionally, a piece of adhesive tape to mark the problem points on the glass as you find them.

Step 1: Open the window and place the sheet

Open the sash. Place the sheet of paper over the frame, in the area where the gasket will press when you close — leave half of the sheet on the inside, so you have something to pull, and half on the outside of the sealing contour.

Step 2: Close the window over the sheet

Close the sash normally and fully operate the handle, as if closing the window for winter. The hardware must pull the sash onto the gasket with its normal clamping force — otherwise the test is not conclusive.

Step 3: Pull the sheet

Grab the free end of the sheet and pull gently, horizontally. Interpret according to how the paper behaves:

If the paper tears or offers firm resistance and you have to pull hard — perfect, the gasket clamps correctly at that point. No air enters there.

If the paper comes out easily, sliding without effort — at that point the gasket is NOT pressing enough. Air enters there and the whistling may come from there. Mark the point with a piece of adhesive tape on the glass.

Step 4: Repeat all around the contour

Repeat the test at a minimum of 8 points around the entire window perimeter: the 4 corners, the middle of each side, and always at the hinges and on the side opposite the handle. These are the areas where leaks appear most often. In the end you will have a clear "map" of the points where the paper comes out easily — that is exactly where the problem is.

How to interpret the result

What you found also tells you the likely cause:

If the paper comes out easily only on the side opposite the handle or near the hinges, but clamps well near the handle, most likely the hardware is misadjusted or the clamping pressure is too low — this is solved by adjustment, without new parts. See How to adjust Roto hardware for winter/summer mode.

If the paper comes out easily on several sides, uniformly, and the gasket feels hard and cracked to the touch, the problem is with the gaskets — they have lost their elasticity. See When window gaskets need replacing.

If the paper clamps well everywhere, but you still feel a draught — then air is not entering at the sash, but at the joint with the wall, meaning the problem is with the installation, not the window. The full context is in the guide article Why windows whistle when the wind blows.

An alternative test: the flame

If you want a visual confirmation, you can also use a candle or a lighter. With the window closed, move the flame slowly about 2–3 cm from the window contour, on the inside. Where the flame flickers or leans, there is an air current. It is less precise than paper for the clamping force, but useful in strong wind. Be careful not to bring the flame near curtains, gaskets or other flammable materials.

FAQ — The paper test

How do I check if my window is still airtight?

The simplest test: put a sheet of paper on the window frame, close the window over it and pull. If the paper comes out easily, the gasket no longer clamps at that point and air enters there. Repeat all around the contour to find all the problem areas.

What does it mean if the paper comes out easily from one side of the window?

It means that in that area the gasket is not pressing enough — either it is worn, or the hardware is misadjusted. It is exactly the point where cold air enters and where the whistling in the wind may come from. That area needs adjustment or a new gasket.

Does the paper test work on any type of window?

Yes, it works identically on PVC, aluminium and wood windows, regardless of manufacturer, because it measures something universal: how firmly the gasket clamps the sash onto the frame. It is the standard method used even by professional installers for a quick airtightness check.

How often should I do the test?

Ideally once a year, in autumn, before the cold season — that is when it matters most that the windows are airtight. A quick test all around the contour tells you whether you need a hardware adjustment or new gaskets before the cold arrives.

What do I do after finding the areas where air enters?

It depends on the pattern: if it is localised near the hinges or opposite the handle, try a hardware adjustment first; if it is widespread and the gasket is hard and cracked, replace the gaskets; if the paper clamps well but you still feel a draught, the problem is with the installation in the wall and a specialist is needed.

Neofort BIZ checks, adjusts and re-seals Salamander PVC and Alumil aluminium joinery in Bucharest and Ilfov. If the paper test revealed air leaks, request a free on-site assessment.