This Beautiful-but-Boring HVAC Stock Has Quietly Crushed the Market — and Its Run Is Far From Over

Comfort Systems USA (FIX 2.34%) stock is up an incredible 1,240% over the last three years, and up 116% in 2026 alone as I write. It’s an astonishing run that speaks to the explosion in artificial intelligence (AI) data center spending in the period. It’s a run that could easily continue, and at the same time end abruptly. Here’s what you need to know before buying the stock.

A hidden AI infrastructure stock

The mechanical and electrical services contractor is enjoying an unprecedented boom in demand coming from spending on AI infrastructure. The company constructs, installs, and services heating, ventilation, and air conditioning (HVAC); as well as plumbing, electrical, and associated services for commercial and institutional customers.

Given the critical importance of HVAC and electrical systems to data centers and the ongoing arms race to build out AI infrastructure, the company’s services have come into great demand. A look at the company’s backlog reveals why the stock is up massively. To put the figures into context, the company’s estimated 2026 revenue is almost $12 billion, so the backlog alone represents a full year’s revenue.

Why Comfort Systems stock has soared

There’s little doubt that AI-related spending has actually accelerated in 2026. GE Vernova (gas turbines that power AI data centers) and nVent (electrical connection and protection systems) raised guidance on the back of improving end markets driven by the same hyperscaler spending that drives Comfort Systems’ orders and backlog.

Still, the question is: How long can it continue?

What’s next for data center spending?

The improvement in the stock price in 2026 comes as the bulls have won the argument over the medium-term direction of spending. The announced capital spending commitments by hyperscalers such as Alphabet and Amazon have exceeded expectations, as evidenced by Comfort Systems’ results as well as those of the two companies referenced above.

Still, while the market has rushed to price in spending commitments over the next few years, there’s a legitimate question of whether AI-related stocks are being priced for post-2030 growth assumptions that might not materialize.

Indeed, a PwC report on future infrastructure spending argues that a shift in spending toward inference rather than language model training (which requires massive computing power) will lead to digital networking spending exceeding data center spending in 2031. In addition, data center spending is expected to decline in the late 2020s, while digital networks (fiber optics, wireless technology) will continue to grow steadily.

What does it mean for investors?

If PwC is right, then it’s dangerous to assume Comfort Systems (which relies more on data center spending than digital networking spending) will grow at the same rate after the late 2020s. On that basis, the stock is worth avoiding, not least as the current Wall Street consensus calls for earnings before interest, taxes, depreciation, and amortization (EBITDA) of $3.1 billion in 2030, compared to the current market cap of $71 billion, according to S&P Global Market Intelligence.

That said, markets rarely move long-term discounted cash flow analyses up or down based on long-term assumptions. Instead, they tend to react to near- to medium-term outlooks, and the reality is that hyperscalers keep ramping up spending expectations. As long as they do so, Comfort Systems USA will continue to receive market support.