I retrovitted the bedrooms (and living room) in my house with a demand controlled fresh air system that contains high quality HEPA and carbon filters. The diffe

I retrovitted the bedrooms (and living room) in my house with a demand controlled fresh air system that contains high quality HEPA and carbon filters. The difference is extremely noticable. Especially when the air quality outside is not good, you feel like you are on a mountain top with crisp, clean air.