1. Height - 20 stories or higher? Tall buildings lose more heat, as stack effect is greater in taller buildings. 2. Exposure - How exposed is the building? High exposure to wind loading results in greater heat loss. 3. Ventilation - Are vents large or small? - The free vent area of existing vents is an indicator of heat loss. 4. Age - Was your building constructed before or after the year 2000? Roof-level infiltration tends to be greater in post millennium buildings where ai