This article presents thermal characteristics of a transparent thin-film heater made of single-walled carbon nanotubes on a glass substrate. A simplified analysis model is developed for predicting the thermal behaviors of the heater and its validity is verified by numerical and experimental results. The analytic solution discloses that the key factors controlling steady thermal performance and transient thermal adjustment. For a thin heater of which the Biot number is very small, the temperature of the heater is determined by the applied gradient of electric potential, the sheet resistance of the nanotube film, and the surface heat transfer coefficient. The time scale required for transient heat-up is a function of the thermal mass of glass substrate and the surface heat transfer coefficient.