Ask most HVAC owners if their business is profitable and they'll say yes, because revenue is up and the bank account isn't empty. Ask them which truck, which tech, or which job type is actually making them money, and most of them can't answer that. That gap is where a lot of profit quietly disappears.

Job costing means tracking revenue and cost at the job level instead of just looking at the business as a whole. For a trades business, that means knowing what each service call actually costs you once you account for labor, materials, drive time, and a fair share of overhead, not just what the invoice says you charged.

Without job costing, it's easy to keep running certain jobs or certain customers at a loss without ever realizing it. A maintenance agreement that seemed like steady recurring revenue might actually be losing money once you factor in the real cost of the visits. A particular truck might be logging plenty of calls but running behind on billable hours compared to the rest of the fleet.

Setting this up doesn't require a complicated system. In Xero, we typically build this out using tracking categories, tagging each job or invoice by truck, technician, or job type. Once that's in place, you can pull a report that shows margin by category instead of just one number for the whole company. That's the difference between knowing you made money this month and knowing exactly where it came from.

For contractors running more than one truck, this is usually the single biggest blind spot in the books. It's also one of the fastest things to fix once the tracking structure is in place, because the data is already flowing through your invoicing. It just isn't organized in a way that answers the question you actually care about.

If you've never seen a per-truck or per-tech profitability report for your own business, that's worth fixing before you're deciding whether to add a fourth truck or replace one that's underperforming.

Jeremy Brewer is the founder of 911 Bookkeepers LLC in Baton Rouge, Louisiana. He worked in the field as an HVAC tech before building books for the trades, and he serves as a licensed paramedic in EMS. He is a Xero Certified Advisor.