Supply House Costs and Material Segmentation: Getting Visibility into Your Biggest Variable Cost

Ask most HVAC or plumbing contractors what percentage of their revenue goes to supply house purchases, and they’ll give you a number. Ask them to break that down by equipment, parts, and supplies—and where the waste happens—and you’ll get silence.

Materials are typically 30-40% of revenue in HVAC and plumbing. But here’s the uncomfortable truth: most shop owners have less visibility into material costs than they do into technician payroll. And that costs them.

I’ve audited supply house spending for 35+ contractors. For a $5M company, a typical audit surfaces $50K-$100K in annual waste: unauthorized purchases, invoice mismatches, rebate leakage, off-account buying, and poor supplier relationships. That’s 1-2 points of margin, recovered without raising a single price.

Getting visibility requires three things: segmentation, tracking, and accountability. Let’s walk through each.

Why Materials Are Your Least-Tracked Cost

Labor is obvious. You see payroll every week. Overhead is budgeted. But materials? They hide.

A technician buys a hard-start kit on Tuesday. Buys refrigerant on Thursday. Buys a capacitor and compressor on Saturday. Three invoices, three suppliers sometimes, three different accounts if techs have personal vendor relationships.

By month-end, you have 200+ invoices across 4-5 suppliers. Your bookkeeper reconciles them to COGS. You see a number (“COGS was 38% of revenue”), but you don’t see where the money actually went.

Contrast this to labor: you have one payroll system, one report, clear visibility. Why? Because it’s centralized and consistent.

Materials are decentralized and inconsistent. Techs have ordering authority. Purchasing rules aren’t documented. There’s no central material tracking. By the time you realize there’s a problem, you’ve been leaking margin for six months.

COGS Segmentation: Breaking It Down

Your first task is to segment materials by category. This requires a chart of accounts (COA) overhaul. Most contractors have one account: “Materials” or “COGS.” Not enough.

You need at least these categories:

Equipment: Compressors, condenser coils, furnace assemblies, air handlers, water heaters. High-ticket items, major materials, often pre-quoted to customers.

Parts: Capacitors, contactors, thermostats, refrigerant, motors, expansion devices. Mid-ticket, common replacements, margin-critical because they’re repeatable.

Supplies: Ductwork, insulation, sealant, fasteners, piping, wire. Low-ticket, bulky, often under-tracked because they seem minor individually.

Tools & Equipment: Gauges, hoses, test equipment, power tools. Separate from job materials—these are capital-adjacent and need different accounting treatment.

Other: Misc, educational materials, trade show materials. Catch-all, should be under 2 percent of COGS.

Why does this matter? Because each category has different margin characteristics.

Example breakdown for a $1M HVAC shop with 35% COGS:

Now you can ask intelligent questions:

• Why is “Other” 6% of COGS? Is that waste leaking, or legitimate miscellaneous spend?
• Equipment margin is 28%—is that locked in by customer quotes, or is there pricing flexibility?
• Supplies at 45% margin are our highest-margin material category—should we be upselling more?
• Parts at 42% margin are our second-largest category by volume—any discounting happening here we’re not seeing?

You can’t ask these questions if you don’t have the breakdown.

Tracking Supply House Invoices vs. Purchase Orders

Here’s where discipline becomes profitable. Most contractors operate on a “bill first, account later” model: tech buys material, supplier invoices, invoice gets paid. At month-end, it all gets coded to COGS.

Better shops use a purchase order (PO) system: request sent to supplier before purchase, PO number issued, tech references PO on the order, invoice matches PO on receipt.

Why does this matter? Three reasons:

Reason 1: Catch Unauthorized Purchases A technician shouldn’t be buying a $300 compressor without your knowledge. With a PO system, unauthorized purchases get flagged. With bill-first, you find out at month-end.

Reason 2: Match Invoices to Actual Jobs PO system lets you tag materials to specific jobs. Month-end reconciliation is clean. Bill-first means you have 200 invoices and a guessing game about which jobs they belong to.

Reason 3: Negotiate Pricing and Terms If your supplier sees you’re planning to order $180K in parts this year (via POs), they’ll compete harder. If they only see actual bills trickle in weekly, they have no leverage to improve terms.

How to implement: Use your accounting software (QuickBooks, Wave, Xero, etc.) to create POs. Set approval limits: technicians can PO up to $500 without approval, $500-$2,000 needs manager sign-off, >$2,000 needs owner approval. Suppliers acknowledge POs. When invoice arrives, match to PO and approve for payment if amounts align.

Yes, this adds steps. But it saves 10x in caught waste and margin recovery.

Rebate Programs and Volume Discounts: Money Left on the Table

HVAC and plumbing suppliers run rebate programs constantly. Buy 15 Goodman units in Q1, get a rebate of $800-$1,500. Most contractors never claim them.

Similarly, volume discounts are often unstated. If you ask for pricing on 10 units vs. 1, the per-unit price might drop 5-8%. But if you’re not tracking volume or comparing suppliers, you’ll never know.

What you should be doing:

Rebate tracking: Create a spreadsheet: supplier → program → purchase period → units purchased → rebate per unit → total rebate due → claimed (Y/N) → date received. Review monthly. Most suppliers require you to claim within 30-60 days of purchase or the rebate expires.

Conservative estimate: rebate leakage costs the average HVAC shop $8K-$12K annually. That’s 0.8-1.2% of revenue sitting unclaimed.

Volume discount negotiation: Call your top 2-3 suppliers quarterly. “We bought $XXK from you last quarter. What volume discounts apply at our level? What if we committed to $XXK annually?” Get it in writing. Update your internal pricing guides.

I’ve seen contractors negotiate 3-5% annual volume discounts simply by asking and showing commitment. On a $350K material spend, that’s $10.5K-$17.5K recovered.

The Off-Account Buying Problem

“Off-account” means a technician buys materials using their own money or personal credit card, then submits for reimbursement. Or they have a personal account at a local supplier (brother-in-law’s shop, retired contractor, etc.) and charge it there instead of through company accounts.

Why does this happen? Usually because the company account is “too slow” or “doesn’t have the item in stock.” Sometimes because the technician gets a personal discount.

Why is it a problem?

Problem 1: Hidden Costs You’re not seeing all material purchases. Your COGS analysis is incomplete. You think materials are 34% of revenue, but they’re actually 36% because $30K of purchases went through the tech’s personal account.

Problem 2: No Supplier Leverage If your actual spend is scattered across 3 company accounts + tech personal accounts + side vendors, you have no consolidated purchasing power. You’re leaving volume discounts on the table.

Problem 3: Pricing Opacity You don’t know what the tech paid. Maybe they got a better deal. Maybe they overpaid. You have no benchmark.

Problem 4: Reimbursement Creep Tech buys $150 in parts, submits $165 receipt. You pay $165. No one’s verifying accuracy. Over a year, this adds up.

How to eliminate it: Policy change. “All materials must be purchased on company accounts. No reimbursements for personal purchases. If an item is out of stock, contact dispatch before buying elsewhere.” This forces centralization. Yes, some technicians will resist. But the margin recovery pays for the friction.

Invoice Matching: Catching Discrepancies

Your supplier invoices should match your POs and your receipts. Often they don’t.

Common mismatches:

Mismatch 1: Quantity Variance You ordered 2 compressors. Invoice shows 2. But you only received 1. Invoice gets paid anyway. Supplier ships the second one later (or never) and you’ve effectively overpaid by $600.

Mismatch 2: Pricing Variance You negotiated a price of $285 per unit. Invoice shows $310. You assume it’s correct and pay. Across a year of orders, that pattern quietly costs $4K. Easy to miss.

Mismatch 3: Freight Overcharge Invoice shows freight of $75 on a $400 order. No freight was discussed. You pay it. It stays in COGS as materials cost, inflating your material percentage.

Mismatch 4: Duplicate Invoice Invoice #1234 arrives in January. Same invoice arrives again in March (system glitch on supplier end). You pay both. No one notices because you’re not reconciling.

How to catch it: Simple three-step process:

1. Receipt: Verify materials arrived match the invoice quantity and description.
2. Price: Spot-check invoice pricing against your cost baseline or last invoice for the same item.
3. Amount: Add up the invoice line items yourself before paying. Supplier math errors happen.

Assign this to someone—dispatcher, office manager, or bookkeeper. 20 minutes per week. Average recovery: $500-$800/month from catching overcharges and duplicates.

Chart of Accounts Setup for Material Tracking

Your chart of accounts should mirror your business logic. If you’re segmenting materials by equipment, parts, and supplies, your COA needs to reflect that.

Recommended structure:

5000-5099: Equipment

• 5010 – HVAC Equipment (condensers, furnaces, etc.)
• 5020 – Plumbing Equipment (water heaters, tanks, etc.)
• 5030 – Electrical Equipment (panels, etc.)

5100-5199: Parts

• 5110 – Compressors & Motors
• 5120 – Refrigerants & Fluids
• 5130 – Controls & Thermostats
• 5140 – Valves & Fittings

5200-5299: Supplies

• 5210 – Ductwork & Insulation
• 5220 – Piping & Tubing
• 5230 – Fasteners & Hardware
• 5240 – Sealants & Lubricants

5300-5399: Tools & Equipment (Capitalized)

• 5310 – Small Tools (under $500 per item)
• 5320 – Test Equipment

5900-5999: Other/Misc

When a technician or dispatcher codes a material purchase, they use this chart. By month-end, you can generate a report: “COGS by Category.” You see exactly where money went.

Most contractors use QuickBooks. Your accountant or bookkeeper can set this up in 2 hours. Worth every minute.

What Good Reporting Looks Like

After you’ve implemented segmentation and tracking, your monthly reporting should include:

1. COGS by Category

Look at this report and immediately ask: Why did “Other” jump 1.2% month-over-month? Investigate. Fix.

2. Supplier Spend Summary

This shows you’re relying on one supplier for 37% of spend. Concentration risk. Call them and lock in better terms. Also: “Local Supply House” 22% of spend with no rebates? Wrong supplier relationship.

3. Off-Account Purchases

Track this: Do any technicians still have personal reimbursements? How much? Eliminate them.

4. Invoice Discrepancy Log

Monthly total of overcharges, duplicate invoices, quantity mismatches caught and corrected. YTD recovery. Accountability.

Common Issues and How to Fix Them

Issue 1: Technicians Buying Off-Account Policy change + consequences. “All purchases on company accounts only. Violations result in repayment or termination.” Enforce for one month. Problem solved.

Issue 2: Missing Purchase Orders Implement system: no invoice gets paid without PO match. Suppliers will adapt. Technicians will adapt.

Issue 3: Rebate Leakage Assign rebate tracking to one person. Spreadsheet + monthly review. Budget 4 hours/month. ROI is 10x.

Issue 4: Invoice Mismatches Not Caught Three-step matching process + owner spot-check of 10% of invoices monthly. Audits catch lazy approval.

Issue 5: High “Other” / Misc Spending Month-by-month line-item review. Is it legitimate business spend or hidden waste? If it’s >3% of COGS, investigate every line item until it’s explained.

What This Means for Your Margins

Getting tight control over materials can add 1-2 points to gross margin. For a $2M business, that’s $20K-$40K in additional profit. For a $5M business, it’s $50K-$100K.

This isn’t coming from price increases or reducing material costs directly. It’s coming from:

• Claiming rebates you were leaving on the table ($8K-$12K/year)
• Negotiating better volume discounts ($10K-$15K/year)
• Catching supplier overcharges and duplicates ($6K-$10K/year)
• Eliminating off-account purchases that lose margin ($5K-$8K/year)
• Reducing waste and unauthorized purchases ($8K-$15K/year)

For a shop in the $2M-$3M range, these add up to $37K-$60K in annual recovery. Most of it requires no capital investment, just discipline.

Next Steps

Week 1: Audit your chart of accounts. Create material categories (Equipment, Parts, Supplies, Tools, Other). Assign account numbers.

Week 2: Set up PO system in your accounting software. Establish approval limits.

Week 3: Call your top 3 suppliers. Ask about volume discounts and rebate programs. Get it in writing.

Week 4: Create a rebate tracking spreadsheet. Review all supplier invoices from the last 3 months. Identify and claim unpaid rebates.

Month 2: Implement invoice matching process. Train dispatcher/office manager on three-step verification. Catch and correct one month of invoices manually.

Month 3: Run your first “COGS by Category” report. Compare to budget. If categories are higher than expected, investigate line item by line item.

Related: Home Services Overhead Rate: How to Calculate and Benchmark

About the Author

Raymond Gong

Raymond Gong is one of the senior partners of Profitability Partners, a fractional CFO and accounting firm built exclusively for home services companies — HVAC, plumbing, electrical, and roofing operators doing $5M–$30M in revenue. Prior to Profitability Partners, Raymond was a private equity professional at Black Diamond Capital Management and Third Lake Partners, a large family investment office. Raymond runs the books, the reporting, the profitability optimization, and the exit prep for contractors nationwide, working daily inside ServiceTitan, Housecall Pro, and QuickBooks — turning messy operational data into financials owners can actually run the business on, and that buyers and lenders take seriously. Raymond is a graduate of Vanderbilt University and is based in Tampa, FL.

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Raymond Gong

Raymond Gong is one of the senior partners of Profitability Partners, a fractional CFO and accounting firm built exclusively for home services companies — HVAC, plumbing, electrical, and roofing operators doing $5M–$30M in revenue. Prior to Profitability Partners, Raymond was a private equity professional at Black Diamond Capital Management and Third Lake Partners, a large family investment office. Raymond runs the books, the reporting, the profitability optimization, and the exit prep for contractors nationwide, working daily inside ServiceTitan, Housecall Pro, and QuickBooks — turning messy operational data into financials owners can actually run the business on, and that buyers and lenders take seriously. Raymond is a graduate of Vanderbilt University and is based in Tampa, FL.