Dual pipe heat exchanger of boiler for house heating and hot water

A double pipe heat exchanger comprising:

• a first double pipe and a second double pipe, wherein each one of the first double pipe and the second double pipe including:
• one outer pipe to which combustion heat is applied from a burner of a combustion chamber, and
• two inner pipes arranged in parallel, each of which is inserted in the outer pipe,
• a returned heating water pipe through which a cold returned heating water flows is connected to the two inner pipes of the first double pipe at one end of the outer pipe of the first double pipe;
• a cold water pipe through which a cold water flows is connected to the two inner pipes of the second double pipe at one end of the outer pipe of the second double pipe;
• wherein fluid pathway caps are installed at both ends of each outer pipe in sidewalls of the combustion chamber such that each fluid pathway cap covers each end of the two inner pipes, wherein the other end of the outer pipe of the first double pipe is connected to the one end of the outer pipe of the second double pipe via one of the fluid pathway caps, wherein the other end of the outer pipe of the second double pipe is connected to the one end of the outer pipe of the first double pipe via one of the fluid pathway caps.