An in-line fluid heater including a heater housing that contains a parabolic lamp vessel which houses an infrared lamp. A parabolic reflection vessel in the heater housing is separated from the parabolic lamp vessel by a convex lens. A quartz plate seals the heater housing, and at least one, and typically, multiple leak detectors may be provided in the heater housing. The interior reflective surface of the reflection vessel reflects the heat energy in parallel rays through the quartz plate and to the fluid to be heated. The leak detectors may be connected to an RC circuit which operates a controller to actuate a buzzer or alarm and terminate operation of the heater upon leakage of fluid into the heater housing.