What is positive and negative pressure?

The isolation technique that generated and maintained by the ventilation system e.g. HVAC that
removes exhaust air from the room which used in pharmaceutical production area to prevent cross-
contamination from room to room. It includes ventilation system that generates negative pressure to
allow air to flow into the isolation room but not escape from the room as air will naturally flow from
areas with higher pressure to areas with lower pressure, thereby preventing contaminated air from
escaping the room.

In simple word a room will be in negative pressure if the air pressure in the room is lower than that of
the surrounding air pressure. So no air flow from the room under negative pressure. If any leakage exist, air will ingress (flow inward). The harmful vapor or odor is kept inside the room and control exhaust system is done safely.

Air is allowed into the room through a gap under the door. Except for this gap, the room should be as
airtight as possible, allowing no air in through cracks and gaps such as those around windows, light
fixtures and electrical outlets. Leakage from these sources can compromise or eliminate room negative pressure.


Positive pressure = more fans acting as intake than exhaust, they would BLOW into the case, increasing the pressure.

Negative pressure = more fans acting as exhaust than intake. They would SUCK out the case, decerasing the pressure.

Negative pressure is better for cooling because it eliminates any hot spots, but causes dust issues as the case will be getting air in anyway it can, which usually includes case seams, cracks, and unfiltered openings.

Positive pressure is better for keeping a clean case because you can put a filter on each intake fan, eliminating the dust potential. But this can cause pockets of hot air to form in the PC case.