The North American hydronics industry has dealt with primary/secondary piping systems for years. Most hydronic heating pros know the principles used in these systems.
Still, based on questions I’ve had over the years, it’s evident that some aspects of primary/secondary coupling of circuits remain “mysterious.” One of the common questions is, “What happens if the flow rate in the secondary circuit is greater than the flow rate in the primary circuit?” Other questions related to the same concept include: