I've been auditing electric bills exclusively and a client just asked me to look at their gas bills too. I said yes but honestly I don't know where the errors typically hide on gas bills. Is it mostly the same — rate classification, meter issues — or is gas a completely different animal?
Gas vs electric — what's different about auditing gas?
Same principles, different details. The big error categories on gas bills are: wrong rate class (just like electric), pressure correction factor (Phil covered this above), wrong BTU conversion factor, transportation vs sales service classification, and weather normalization errors on temperature-sensitive accounts. Gas tariffs tend to be simpler than electric because there's no demand component for most commercial accounts. But the billing calculations can be trickier because of the volume-to-energy conversions.
Derek covered the main areas well. I'd add one thing that catches people: in deregulated gas states, the customer may be buying gas supply from a marketer while paying the utility for transportation only. Make sure you're auditing both the supply and transport charges. I've seen errors on the transport side that the supply marketer would never catch, and vice versa. Also check whether the customer qualifies for an interruptible gas rate — manufacturers with backup fuel capability often qualify and the savings can be 15-20% on the transport charges.
This is helpful. Sounds like I can leverage most of my electric audit skills but need to learn the gas-specific items like pressure factors and BTU conversions. Going to start with the tariff book.
Welcome to the gas side. It's less crowded than electric auditing which means less competition and more low-hanging fruit.