The invention relates to a replacement system providing replacement air to inerting system, which includes a plurality of heat exchangers and a compressing device, is configured to prepare in parallel a medium bled from a low-pressure location of an engine and flowing through a plurality of heat exchangers into a chamber. The compressing device is in communication with the plurality of heat exchangers and regulates a pressure of the medium flowing through the plurality of heat exchangers. The replacement system employs a subsystem to treat the medium from the low-pressure location of the engine before it is received by the inerting system.