A method of designing a buffer system for a gas turbine engine according to an example of the present disclosure includes, among other things, configuring a heat exchanger to define a first inlet and a first outlet fluidly coupled to each other and a second inlet and a second outlet fluidly coupled to each other, configuring the first inlet to receive air from first and second air sources that are selectively fluidly coupled to the first inlet, configuring the second inlet to receive air from a third air source fluidly that is coupled to the second inlet, and configuring the first outlet to provide cooled pressurized air to multiple fluid-supplied areas that are located remotely from one another and that are fluidly coupled to the first outlet, the multiple fluid-supplied areas including a bearing compartment of a gas turbine engine.