Part of the joy of spring cleaning is being able to open up the windows, letting in fresh air and warm sun rays. But how can you keep your indoor air fresh when it's humid or too hot or cold outside? There are several ways maintain clean, healthy, and fresh indoor air without opening the windows. For example, you can install a mechanical ventilator in your HVAC system, which will bring in fresh air from outside and filter it through the HVAC system before it reaches your air registers. You can then appreciate fresh, filtered air flowing throughout your home.