An indirect heater assembly (10) comprises a radiant tube heater (12) and a fan (14) for generating an air flow over the heater (12). In an preferred embodiment and in another aspect, the radiant tube heater (12) comprises a radiant tube burner, an elongate tube 16 and a spiral tube (23) connected to the elongate tube (16) by a U-shaped tube (25). The spiral tube (23) extends around the elongate tube (16) coaxially thereof.