WHAT TO LOOK FOR Buildings which have inadequate makeup air (or excess exhaust) and are operating with a negative pressure condition have several common characteristics. These include: A) The building is uncomfortable and has noticeable temperature fluctuations. The perimeter of the building may be cold and drafty due to high infiltration at the same time that other central areas may be overheated. B) Exterior doors may be difficult and hazardous to open. A door which slams shut can result in broken bones and serious injuries. C) Cold drafts can be felt rushing into the building around cracks and openings. D) Exhaust systems do not perform at the rated design capacity. Inadequate or ineffective exhaust may result in a hazy atmosphere. E) Gravity vents from heating equipment or process may back-vent into the conditioned space, drawing potentially hazardous products of combustion (Flue Gases) into the building.