With advances in building science we've learned how to build tighter and much more efficient structures that actually have better indoor air quality than a ‘loose' old building. These advances were not made without bumps and bruises. Building Scientists emerged as attempts to tighten building in the 70s and 80s resulted in problems due to lack of understanding. Study of the home as a system has solved these problems and yielded incredible results in performance and healthy living spaces.
An example of simple ventilation would be an exhaust fan. New construction code calls for exhaust fans where older homes never had them. Places where moisture and odor emanate such as kitchens and bathrooms. Controlling moisture in homes gets more important the tighter the home gets.
A simple air exchanger has two small fans, or some other similar concept. One fan pulling stale air out and one introducing fresh air. This could be installed in any space you want to ventilate or hooked up to your HVAC system if you have a fresh air problem in your whole home.
These systems do everything that a simple air exchanger does but they incorporate an important advantage. They exchange heat and or humidity between incoming and outgoing airstreams. In the winter the warm outgoing air transfers heat to the cold incoming air without the two streams touching.