An infrared calorimeter system for measuring energy flux in a noisy electromagnetic environment has been developed. A thin (13 &mgr;) oxidized stainless‐steel foil is heated by energy flux and its temperature is determined by measuring the infrared emission from the back surface of the foil. The radiation is transported to the detector, which is located inside a double‐shielded enclosure, through a nylon‐tube infrared telescope. The calculated response time is 12 &mgr;s, and the measured peak‐to‐peak noise is equivalent to 0.4 mJ/cm2deposited energy.