Boilers: identify the type when water circulation is driven by a centrifugal pump Circulation of water in the boiler is provided by a mechanical pump rather than by density difference or natural convection. Choose the correct boiler classification.

Concept
When circulation is produced by a pump, the unit is termed a forced circulation boiler. Natural circulation relies on density difference between hot and cold water; forced systems use a centrifugal (circulating) pump to move water through the evaporator, risers, and downcomers.

Why the others are wrong
Internally/externally fired classify furnace position, not circulation method. Natural circulation is explicitly without a pump.

Final Answer
Forced circulation boiler