In most cases the crack will follow a curve in the shape of an hourglass.
How to detect cracks in window and door.
Inspect windows and doors for air leaks.
Stress cracks can form when there is a large difference between the temperatures inside and outside your home.
The most common cause of these stress cracks is extreme temperature fluctuation.
Check to see if the caulking and weather stripping are applied properly leaving no gaps or cracks and are in good condition.
If smoke blows sideways you likely have a leak.
You can tell that a pressure crack has occurred due to the shape of the break in the glass.
Doors and windows another way to test the seriousness of a wall crack is to open and close internal doors to bedrooms and bathrooms and evaluate whether the doors stick.
Hold a lit incense stick by windows outlets doors and any other suspected areas.
You can usually find them near the edge of the window glass.
Check the exterior caulking around doors and windows and see whether exterior storm doors and primary doors seal tightly.
The windows cannot withstand the pressure of these scenarios and will crack as a result.