To prevent flue gases from escaping, the spaces between cast-iron sections are:

The correct response highlights the importance of sealing the spaces between cast-iron sections to ensure that flue gases do not escape into the environment. Using a high-temperature rope gasket is a common and effective method for achieving this. These gaskets are designed to withstand high temperatures and maintain a tight seal even under the thermal expansion and contraction that occurs in heating systems.

The effectiveness of the high-temperature rope gasket comes from its ability to expand and contract without losing its sealing properties, thus preventing any leaks of flue gases. This is crucial for maintaining safety and efficiency within the system, as escaping flue gases can be hazardous and reduce the overall operational effectiveness of the heating equipment.

The other options do not provide the same level of effectiveness for sealing flue gases. For instance, welding might compromise the integrity of the cast-iron sections due to heat stress, while insulation primarily serves to retain heat rather than provide a sealing function. Painting, on the other hand, does not contribute anything to preventing gas leaks and is not a suitable method for sealing connections in such applications.