Payroll doesn't wait for the weather. If you run an HVAC business, you know revenue can drop sharply between peak season and the slow months, by half or more in some markets. But knowing that and planning for it are two different things. A monthly profit and loss statement can't tell you whether your account will cover payroll in week nine of a cold streak, or whether an equipment deposit due in March will collide with another big payment you forgot was coming.
This guide walks through building a 13-week rolling cash forecast designed for the revenue rhythms and recurring obligations of HVAC contracting: why your current reports leave blind spots, what your books need to look like first, and how to map inflows and outflows precisely enough to keep the trucks on the road year-round.
A contractor watching strong summer revenue fall off a cliff by winter isn't experiencing a business failure. It's a seasonal decline arriving on a predictable schedule, and it still catches experienced owners short every year.
The cliff exists in every market; only the calendar shifts. Sun Belt contractors peak in the long cooling season. Northern contractors may have a heating peak and a cooling peak.
What makes the cliff dangerous isn't the slow season itself. It's the lag between when peak revenue was earned and when the bills tied to it come due. Payroll doesn't pause. Fleet payments, insurance premiums, supplier invoices, and equipment financing don't care that your dispatchers are idle.
Margins can look strong in peak months, and that creates a false sense of security. When the same fixed overhead gets spread across a fraction of normal revenue in the slow months, margins compress hard. The business hasn't become unprofitable. Cash timing has become the survival variable.
Most contractors who struggle in the slow season aren't running bad businesses. Their cash is tied up in receivables from the end of peak season, locked in equipment deposits paid weeks before the customer's balance arrives, or missing a reserve that was never set aside. The company is solvent on paper. The checking account tells a different story on payroll Friday.
A monthly P&L reports revenue when it's earned or invoiced, not when the payment hits your bank. A contractor can post a profitable October on paper while the account can't fund the November 1 payroll. Both statements are technically correct, and that's the problem.
Accrual statements answer a different question. They measure business performance over a period, which is useful for taxes, benchmarking, and lenders. They aren't built to tell you whether a specific payment will clear on a specific date. A cash forecast predicts actual receipt and payment dates. A billing projection estimates invoiced amounts. You need both, and confusing them is where slow-season payroll surprises are born.
A 13-week forecast is only as accurate as the data feeding it. Dirty books don't produce reliable projections. They produce confident-looking ones that point you the wrong way.
Check your revenue categorization first. Income should be broken out by job type: residential replacement, commercial maintenance, service agreements, and new construction. Each has its own payment rhythm. A residential replacement often collects a deposit at signing and a balance at completion. Commercial maintenance usually runs on standard commercial terms. Service agreements bring in payments on a fixed schedule. Lumping them into one "Revenue" line erases the timing information the forecast depends on.
Split equipment and materials from labor. Supplier payments and payroll run on completely different schedules. Your equipment deposit may be due three weeks before the job closes, while payroll runs every two weeks regardless. When those share an account, you lose the timing distinction.
Reconcile to last week, not last month. Reconciliations that lag by 30 days give you a wrong starting cash balance. Reconcile weekly so the number in row one of your model is actual cleared cash.
These three conditions aren't refinements to add later. They're the foundation. At 911 Bookkeepers, getting them in place is the starting point for every HVAC client.
A 13-week rolling cash forecast is a week-by-week projection of every cash inflow and outflow over a 90-day window. Each Monday, you drop the oldest week, record its actuals, and add a new week 13 at the end. The window always looks 13 weeks ahead.
Why 13 weeks? It's one full quarter: long enough to catch obligations already on the books but not yet due, short enough that week-level timing is still realistic. Shorter than about eight weeks, and you miss slow-season payroll runs and supplier deposits already committed.
It isn't a budget. A budget gets set once a year and compared to actuals afterward. A rolling forecast is a living document. Each week, you look at why last week's actuals differed from the projection and adjust your forward assumptions. That habit is what makes it a decision tool instead of a history log.
Three confidence zones match how HVAC work flows:
The point isn't perfect prediction. It's seeing problems while you still have room to act. A cash gap in week nine, spotted in week three, gives you six weeks to make collection calls, line up credit, or delay a discretionary purchase. The same gap discovered the Thursday before payroll gives you nothing.
Start with confirmed bookings. List every job under contract or dispatched, and give each two dates: the expected invoice date and the expected cash receipt date. They aren't the same. Residential service calls often collect within a few days of completion. Commercial work commonly runs Net 30 to Net 45, so cash from a job invoiced in week two may not land until week six or seven.
Segment by job type:
Build a historical baseline for weeks 5 through 13. Pull 12 months of revenue by job type and calculate average weekly inflow for each seasonal period. That becomes your default assumption for weeks without confirmed bookings.
Be honest about collection timing. Not every residential invoice gets paid at the door. Forecast your actual collection history, not same-day payment.
Include every non-job inflow on its actual date. Manufacturer rebates, tax refunds, owner contributions, and credit line draws all belong in the forecast with specific expected dates.
Payroll first. For most HVAC companies, wages are the largest and least negotiable line. Enter every payroll date across all 13 weeks before anything else. The payroll tax deposits that follow each run are separate outflows with their own due dates. Flag every week where the running balance after both would fall below your minimum operating cushion. That flag is the early warning the forecast exists to produce.
Equipment deposits are a stealth drain. Enter each pending purchase as two items: the deposit date and the delivery date. Cash leaves weeks before the customer's balance arrives.
Supplier and subcontractor payments go on invoice due dates, not job completion dates. Net-30 terms mean a job finished in week two creates a payment in week six. Entering it at completion makes the near term look better than it is.
Pre-load fixed overhead. Fleet payments, insurance, software, rent, and loan payments don't take a slow-season break. Load them into every week at the start so none get forgotten.
Treat reserve transfers as a real outflow. Some contractors use a rule of thumb of setting aside 35% to 40% of peak-season profit for the slow months. Whatever your number, schedule the transfer as a weekly or biweekly line during peak months so the reserve builds on purpose instead of being whatever's left in December.
Service agreements look like the cleanest line in the forecast: predictable, contracted, recurring. The cash timing underneath is more complicated.
In your books, a prepaid agreement is a liability until the visits are delivered. In the cash forecast, it's simpler: record the inflow on the date the cash arrives, because the forecast tracks money movement, not revenue recognition.
What you do need to watch is renewal clusters. A block of 20 agreements signed in October renews the following October, creating an inflow spike in an otherwise slow month. Leave that out and you understate available cash for those weeks.
Outflows need the same precision. Spring and fall tune-up pushes often compress into a few weeks, stacking tech time and filter and refrigerant costs into a short window. Put those costs in the weeks the visits are actually scheduled, not averaged across the year.
If you have a meaningful number of agreements, keep a simple agreement schedule with one row per customer showing next visit date, renewal date, and payment status, and pull weekly totals from it into the forecast.
Any reserve rule of thumb is a starting point, not an answer.
Northern contractors face a different pattern than the Sun Belt. A heating peak and a cooling peak mean two ramp-ups instead of one long slow season. The gap between peaks may be narrower, but each transition needs equipment deposits and pre-season hiring funded from the previous season's cash.
Revenue mix matters as much as climate. Contractors with a lot of commercial maintenance often see steadier month-to-month revenue than replacement-heavy shops. That may justify a smaller reserve, but commercial work brings its own timing risks: retainage held for months and payment cycles much longer than residential.
Your right reserve comes from your own history. After two or three rolling 13-week cycles, your actual slow-season cash low point becomes visible. From there you can work out the reserve you need to stay above your minimum balance through the trough, without over-reserving cash that could fund growth. An HVAC-experienced bookkeeper can often find that low point from your historical books before you finish your first forecast cycle.
A forecast built once and filed away is worse than no forecast. It creates false confidence while actual cash quietly drifts from the plan.
The weekly update takes under 30 minutes when the books are current: enter last week's actual receipts and payments, compare them to the projection, adjust forward assumptions for anything that changed (a delayed delivery, a slow-paying commercial account, an unplanned repair), and check the updated week-nine balance. That last check is the whole point.
Bring in the people closest to the work. Dispatchers know which jobs close this week. Whoever handles billing knows which commercial accounts are running late. That job-level knowledge is fresher than any monthly accounting review.
A Monday morning routine:
If it takes much longer than half an hour, your books aren't current enough to support the model. Connecting your field service software to your accounting system, with the categories mapped correctly, cuts most of the manual entry.
A model built on miscategorized receipts, lagging reconciliations, or blended job costs will mislead you exactly when you need clarity most.
911 Bookkeepers builds that foundation for HVAC and trade contractors: revenue coded by job type, reconciled accounts, and a chart of accounts that supports a forecast from day one. If you're not sure your books are forecast-ready, book a free call and we'll tell you what it would take.
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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.
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