Abstract: The rib and the block are applicable in heating appliances construction. They have increased operational safety and heat transfer velocity. The rib comprises an upper (1.1) and lower hole (1.2), a joining profile (2), a first (3) and second (4) internal foldings, a third intermediate (5) and a fourth external (6) folding, which ends in a fifth reversed folding (7). The fourth external folding (6) and the fifth reverse folding (7) extend from below to the end of their respective chamfers (8), and at the upper side of the rib, together with the second (4) and the third (5) folding, they connect its two vertical walls via two chamfers (9). Centrally in relation to the upper hole (1.1), on its both sides, and above, on the surface of the second internal folding 4 and the third intermediate folding (5), there are spherical concavities (10), and on both sides of the lower hole (1.2) there are similar spherical concavities (11).