What do you do if you feel that your home or office is stuffy? There are some obvious benefits to opening a window. An open window helps provide a room with air changes, which means the air within a space is exchanged. Air from an open window can replace the stagnant room air, which may be contaminated with mold, bacteria or viruses that could cause illness. The increased ventilation can help decrease carbon-dioxide levels that build over time due to room occupants’ breathing. High levels of carbon dioxide can cause fatigue and headaches. Harmful chemicals that have off-gassed from paints, furniture, or cooking can also be removed with adequate air changes from an open window.