definition
strict definition
indoor air pressure
The difference in air pressure between an enclosed building space and the surrounding space.
Indoor air pressure is the mean or controlled difference between the air pressure within a building or an enclosed building space, and that of the outside air or the air in surrounding rooms. The value can be positive or negative.
A positive difference means that the enclosed space has higher pressure than its reference surroundings. A negative difference means that its pressure is lower.
Equal pressures give a difference of zero even though both spaces contain air at a substantial absolute pressure. The comparison can use adjacent rooms when their pressure supplies the relevant surrounding condition.