This chapter examines modular systems for energy usage in district heating. District heating is becoming more popular in Europe, North America, and other colder countries. The chapter first examines advantages and disadvantages of district heating and the use of small modular renewable heating and cooling grids propagated by the smart CoolHeating project in Europe. Major emphasis in the chapter is on the use of renewable energies for district heating which include biomass combined heat and power (CHP), geothermal, solar, and wind energies. Out of these, the most promising ones are the first three. The chapter also examines the global use of nuclear heat for district heating. Nuclear heat is ideally suited for high- and low-temperature district energy needs. The chapter also examines the use of industrial waste heat and hybrid sources of heat for district heating. The latter includes the use of hybrid geothermal pump for district heating network. Hybrid solar and biomass district heating networks are also becoming very popular. Finally, the chapter examines the role of thermal energy storage in modular district heating including the partnership among thermal energy storage, solar energy, and district heating.