The Internet is the coolest thing. Here's what I found.
The heat of combustion of a material is equal to the heat of formation of the end products minus the heat of formation of the original material.
The heat of formation of CO2, H2O and Propane are -393.5, -285.8, and -103.7 KJ/mol respectively. 3 * (-393.5) = -1180.5. 4 * (-285.8) = -1143.2.
So in the combustion of Propane the Carbon and the Hydrogen make nearly equal heat contributions.