This paper presents preliminary results of calculations of different cases of a geothermal horizontal heat exchanger, where the vertical extraction channel is manufactured as a tube-in-tube exchanger. Such a channel permits control of the mass flow rate of water flowing through its circular (inner) part or annular (external) part, where the latter part also forms the thermal insulation of the exchanger. Results of calculations enable us to control the extent of both outflowing flow rates of water, which will permit us to attain the required temperature of the fluid at an outlet from the exchanger. Due to the fact that the fluid is, at the same time, the energy carrier supplying the heat receivers, the postulated design is equivalent to the equality of rates of acquired geothermal heat and heat demand in receivers of a district heating network for some external temperatures.