The invention discloses a double-temperature hot water system for a natatorium. A tail gas tube of a fire grate biomass boiler is emptied after being connected with a tubular heat exchanger through an induced draft fan; the fire grate biomass boiler carries out constant temperature keeping and heating on pool water; a fixed bed biomass boiler supplies bathing hot water; a coupling of the induced draft fan is in threaded assembly with both a fan shaft and a fan impeller; the thread turning direction is in a working and bearing automatic locking direction; the fan impeller forms threaded rigid connection with the fan shaft after compacting a copper-lead torsion compound pad; and the coupling also forms threaded rigid connection with the other end of the fan shaft through a hoop part. The double-temperature hot water system for the natatorium supplies double-temperature hot water, recovers tail heat of the boiler, more importantly transforms the disassembly and assembly technology of the induced draft fan of the boiler dramatically, can efficiently solve the problem of difficulty in disassembly as threaded assembly of the induced draft fan of the boiler is continuously automatically locked under the loading action and is particularly suitable for convenient and rapid disassembly of a fan of a large boiler after being in threaded locking.