Comfort Systems USA Q3 2026 10-Q: Data Center Boom Drives 54% Revenue Surge and $17.8B Backlog

Behind every massive AI data center and modern semiconductor fab is an intricate web of cooling, power, and ventilation systems. Comfort Systems USA (NYSE: FIX) is one of the primary builders keeping those facilities running, providing commercial heating, ventilation, air conditioning (HVAC), plumbing, and electrical contracting services across the country. Today, we are digging into the income statement from the company's latest Q3 2026 10-Q filing to see how their operations are performing and what we can learn from the numbers.

Surging Revenue and Expanding Margins

In the third quarter ended September 30, 2026, Comfort Systems delivered extraordinary top- and bottom-line expansion. Total revenue jumped 53.7% year-over-year to $3.77 billion, up from $2.45 billion in Q3 2025. While the company regularly acquires regional contractors—such as its August 2026 purchase of Florida-based Boys Electrical Contractors for $63 million—the vast majority of this surge was organic. Same-store revenue (which measures growth at existing locations open for at least a year, stripping out recent acquisitions) climbed 46.3%.

Gross profit kept exact pace with revenue growth, rising 53.7% to $934.5 million and maintaining a steady 24.8% gross margin. However, the real story on the income statement is operating leverage. Selling, general, and administrative (SG&A) expenses grew at a much slower rate (36.8%) than revenue, dropping from 9.4% of total revenue last year to 8.3% this quarter.

Because overhead costs scaled so efficiently, operating income soared 64.8% to $624.6 million, pushing operating margins up to 16.6% (from 15.5% in Q3 2025). Coupled with $16.0 million in interest income earned on its growing cash pile, net income surged 67.7% to $489.0 million, or $13.91 per diluted share.

The diagram below illustrates how Comfort Systems’ third-quarter revenue flowed through its segments and cost structure down to the bottom line:

Data Centers and the Electrical Boom

Comfort Systems divides its business into two reportable segments:

• Mechanical Segment ($2.58 billion revenue, up 42.7%): Encompasses HVAC, plumbing, piping, controls, and off-site modular construction. It generated $469.6 million in operating income (an 18.2% margin).
• Electrical Segment ($1.18 billion revenue, up 84.8%): Focuses on electrical installation and contracting. Operating income here grew 60.4% to $173.6 million (a 14.7% margin).

The primary engine behind both segments is the technology sector—specifically data centers. In Q3 2026, technology customers accounted for 60.8% of total revenue ($2.29 billion), more than doubling from $1.12 billion (45.8% of revenue) in the prior-year period. Together with industrial manufacturing (16.8% of revenue), these massive new-build projects make up over three-quarters of the company's business.

A $17.8 Billion Backlog and Customer Cash

Perhaps the most striking metric in the filing is the company's backlog—the total dollar value of contracted work that has not yet been performed. Backlog reached $17.81 billion at the end of Q3 2026, representing a 26.7% jump in just three months and a 90.0% increase over the $9.38 billion recorded a year ago.

This unprecedented demand has also transformed the balance sheet. When Comfort Systems signs large contracts, it frequently bills customers upfront to fund early-stage equipment and labor costs. These advance payments are recorded as a liability called billings in excess of costs, which ballooned to $3.87 billion (up from $2.12 billion at the end of 2025). This influx of customer cash helped drive $2.54 billion in operating cash flow over the first nine months of 2026, leaving the company with $2.16 billion in cash and zero borrowings on its revolving credit facility—even after spending $349.1 million to repurchase shares at an average price of $1,643.85 per share.

Market Context and Looking Ahead

Competing alongside major specialty contractors like EMCOR Group and Quanta Services, Comfort Systems is in the sweet spot of the U.S. infrastructure and AI data center buildout. Still, executing on a $17.81 billion backlog comes with operational hurdles. Management notes ongoing challenges with skilled labor scarcity, rising wage costs, and intermittent supply chain delays for specialized equipment. Because most of its contracts are fixed-price—meaning Comfort Systems absorbs the risk if project costs run over budget—accurate bidding and tight labor management remain critical. So far, however, the company's expanding margins and record cash generation show it is navigating these pressures exceptionally well.