To determine the required valve rangeability for a hydronic system, you need to consider the system’s operating conditions, including the maximum and minimum flow rates, pressure drops, and temperatures. Rangeability is typically expressed as a ratio of the maximum to minimum flow rates and should be sufficient to accommodate the system’s turndown requirements. A valve with inadequate rangeability may not be able to maintain the desired flow rate during part-load conditions, leading to poor system performance and reduced efficiency. In general, a rangeability of 10:1 or higher is recommended for most hydronic systems.