The severity of climate influences the degree of heating or cooling that is necessary to condition the incoming air. Greater potential exists for the use of complex ventilation strategies combined with heat recovery when ventilation heating or cooling loads are high. A system that may be cost effective in one climatic zone may not be appropriate in another. Building location further influences the choice of ventilation strategy. Locations in urban and city areas, for example, can suffer from poor outdoor air quality derived from traffic fumes and industrial pollutants, while outside noise from passing traffic can be excessive, thus restricting the potential for window opening. Adjacent buildings could create conflict in relation to pre-existing air intakes and exhaust points. Rural locations might be subjected to high pollen concentrations and fungal spores resulting in a need for filtration for hypersensitive individuals.