In working to calculate the marginal cost of electricity of all of the generating units across the country, we first had to calculate the heat rate (MMBtu per MWhr) for each generating unit. The heat rate allows us to attribute the fuel costs, reported at the plant level, to the electric generation, reported at the generating unit level. The heat rate is derived from fuel consumption (MMBtu), reported at the boiler level, and electricity generation (MWh), reported at the generating unit level. To understand the heat rate, one must link up all the boilers with the generators in a given generating unit. Our work to this end uncovered a hole in EIA’s 860 reported boiler generator associations. We filled this hole through a series of matching cartwheels and network analysis.