Copper water tube hydronic boilers has the lowest terminal mass per BTU/hr.

• A. True
• B. Not sure
• C. False
• D. Cannot tell

Answer: (A)

Thermal mass in a boiler context relates to how much heat-storing mass the system has per unit of heat output. Copper water-tube boilers are built with a compact heat exchanger and relatively low water content, so they store less heat for each BTU/hour they produce. That means the terminal mass per BTU/hr is lower than that of heavier designs, like cast-iron boilers, which have more water content and higher mass. The result is quicker response to changing heat demand and faster temperature adjustments, which is why copper water-tube boilers are described as having the lowest terminal mass per BTU/hr.