A process and apparatus for monitoring and/or controlling at least one air conditioning and/or heating plant (1) including a delivery line (3), a return line (4) and service lines (5) hydraulically interposed between the delivery line (3) and the return line (4), each service line (5) comprising at least one thermal exchange unit (7). The process detects a value (φ) of the flow rate of the carrier fluid traversing the thermal exchange unit (7), and determines a temperature difference (ΔT) between the temperature (Tt1) of the carrier fluid, at the first section (5a), detected at a first instant (t1), and the temperature (Tt2) of the carrier fluid, at the second section (5b), detected at a second instant (t2).