Indoor air is dirtier than outdoor air?

At one time or another, you have probably heard that indoor air is dirtier than outdoor air. What’s causing that dirty air and what can we do? Indoor air quality has a direct relationship with how energy efficient our homes have become. Modern buildings are designed to hold heat in the winter and stay cool in the summer. Ventilation systems are designed to exchange the minimum amount of air, maintaining stable indoor temperatures. While benefits of such systems include energy efficiency and lower heating and cooling costs, limiting fresh air exchange can pose significant health risks.