What is a Negative Air Machine?
A negative air machine is a device which removes air from inside an 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 a 'Negative Air Machine' refers to what are effectively Air Scrubbers (such as seen in the picture below). By attaching ducting to the machine, it is able to transport the unwanted 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.