A support assembly (40) for supporting the furnace (22) of a boiler (10) to a support frame (12) of the boiler. The support assembly comprises a first and second assembly parts (56, 8). The first assembly part (56) attaches a pipe (18), f.ex. a downcomer, to a supporting beam (32, 88). The second assembly part (58) attaches the same pipe (18) to another supporting beam (30, 86). The support assembly (40) may be obliquely positioned. Alternatively, the support frame further comprises an oblique, connecting supporting beam (84) that connects the first and second assembly parts. In this case, the first and second assembly parts attach the pipe to the connecting supporting beam (84). The first and second assembly parts define first and second points of support (52, 4) that transmit loads. The first or second assembly part may be a hanger rod. A boiler plant comprises the above-mentioned boiler, support frame for the boiler and support assembly.