A simple mathematical model based on homogeneous flow is developed to study the design and performance aspects of a two-phase, CO₂ based, natural circulation loop. A constant heat flux and constant temperature boundary conditions are used for the heat source and heat sink, respectively. The operating conditions are so chosen that the loop can be used for low temperature refrigeration and air conditioning applications. As the operating temperature is lower than the ambient temperature, the loop pressure shoots up during the loop shutdown. As the standstill pressure during shutdown is a critical parameter, the effect of design and operating parameters on standstill pressure is studied. Results show that the loop size and mass flow rate have to be optimized based on minimum standstill pressure and minimum loop mass. Based on the results obtained, empirical equations are proposed for estimating important design parameters. It is expected that these correlations will be useful in quick sizing of the CO₂ based, two-phase natural circulation loops.