Proton-exchange membrane fuel-cell power generating equipment includes a heat exchanger coupled to a process burner and, therethrough, to a fan. When water needs to be heated, such as during startup, the water is circulated through the heat exchanger and the process burner is operated (ignited) to heat the water. When the water needs to be cooled, such as when a hot water reserving tank is full, the water is circulated through the heat exchanger and the fan is operated, but the process burner is not operated, to cool the water. Water is circulated through part or all of a water system to prevent freezing while the system is stopped. Optionally, the process burner is operated to heat the circulated water. The heat exchanger and other heat exchangers in the system are arranged to efficiently recover heat from burners, a fuel-cell cooling system and exothermic processes.