During large space storms, high-energy electrons from space can enter Earth’s upper atmosphere and create additional fast-moving (superthermal) electrons. Some of these fast electrons bounce back into space and interact with slower-moving electrons in the magnetosphere. This interaction creates a flow of heat, called electron heat flux, that moves downward from space into the upper atmosphere. This heat flow plays an important role in increasing the temperature of the upper ionosphere, which can then affect the lower parts of the atmosphere as well. In this study, we examine how this electron heat flux influenced the upper atmosphere during the powerful May 2024 geomagnetic storm. We use satellite data from the DMSP mission to measure electron temperatures and compare those with results from several physics-based computer models. These models help us understand how fast electrons are produced and how they carry energy into the atmosphere. Our results show that electron heat flowing down from space is an important source of heating in the upper ionosphere during major space weather events.