What is condensing central heating boiler? Why must it be preferred?

Condensing central heating boilers are devices, which obtain additional yield and thus obtain fuel economy by conducting high temperature waste flue gases, which are directly thrown out in classical (conventional) central heating boilers, through re-cycling. Through condensing technology, water vapour in gaseous state thrown out to the atmosphere is liquefied through condensation. The heat emerging during this change of state is used for heating of heater water. Thus, it uses more thermal energy in your heating system by consuming the same amount of fuel, and provides saving up to 20%.