The researchers studied how using energy-efficient windows can reduce heat loss and save energy in buildings in different parts of Russia. They focused on replacing regular windows with double-glazed energy-saving ones to see how much less heat buildings would lose. By calculating a special indicator, they could measure the decrease in heat loss and also factor in less heat coming in through the windows. The results showed that energy-saving windows can really help cut down on the energy needed for heating buildings. This information can be useful for deciding whether it's cost-effective to upgrade to energy-efficient windows in different climates in Russia.