In most cases the crack will follow a curve in the shape of an hourglass.
How to detect cracks in window and door.
The most common cause of these stress cracks is extreme temperature fluctuation.
You can tell that a pressure crack has occurred due to the shape of the break in the glass.
Hold a lit incense stick by windows outlets doors and any other suspected areas.
Turn off the furnace and water heater and turn on exhaust fans.
Stress cracks can form when there is a large difference between the temperatures inside and outside your home.
Stress cracks start off small and then expand and grow across the glass.
Inspect windows and doors for air leaks.
Check the exterior caulking around doors and windows and see whether exterior storm doors and primary doors seal tightly.
Another option for detecting air leaks is using an infrared thermometer which is a non contact thermometer that can measure the ambient air temperatures around window and door frames.
The windows cannot withstand the pressure of these scenarios and will crack as a result.
Check to see if the caulking and weather stripping are applied properly leaving no gaps or cracks and are in good condition.