Three-dimensional maps of the heating of the ISM per hydrogen atom from photoabsorption of X-rays from LMXBs, HMXBs and CXB on the Galactic plane for Monte Carlo sources (top panel) and real sources (bottom panel). In the outer regions of the Galaxy the heating rate approaches the lower bound of ~1.9 × 10^-29 ergs/s/HI coming from absorbed CXB photons. The green cross indicates the position of the Galactic center in each map.