There are a number of considerations to factor when determining the best boiler for your steam generation needs like operating pressure, steam pounds/hour output, demand fluctuation, general application requirments and total cost of ownership, etc.
Two primary boiler types, the firetube boiler and the watertube boiler, are essentially opposite in design. The firetube boiler passes combustion gas inside a series of tubes surrounded by water in a vessel to produce steam, while a watertube instead sends water through a series of tubes surrounded by combustion gas used to transfer heat energy and produce steam.