What is a Negative Air Machine?
A negative air machine is a device that removes air from inside the environment. Generally, it is a fan attached to flexible ducting with the output of the ducting exhausted through a window, its goal is to remove the tainted air from the internal environment and exhaust it outside.
Typically negative air is effectively air scrubbers (like what you see in the picture below) that have the ability to attach ducting to it to exhaust the air outside. Exhausting the air outside creates negative pressure inside the environment and helps inhibit the spread of polluted air to other areas inside the building.
An air scrubber can be used also to recirculate the air inside the property without exhausting outside. The configuration does not affect room pressurisation.