A pressure and/or temperature relief header for use in an HVAC heat transfer coil includes a main body adapted to be secured to bends in fluid coils of the HVAC fluid tube system. The main body includes holes in alignment with holes formed in the bends to enable liquid to pass from the bends into the expansion relief header. The expansion relief headers include a pressure release valve that automatically opens, preferably in response to pressure exceeding a predetermined threshold value or temperature falling below a predetermined value, to release liquid from the expansion relief header and then reseats. A discharge housing collects liquid released through the pressure release valve. A sensor detects the presence of liquid in the discharge housing.