In the three months to June, AAON's BasX division — which builds purpose-built cooling units and pre-packaged outdoor mechanical rooms for data centers — sold more than three times what it did a year earlier. The rest of the company, which makes rooftop air-conditioning units for ordinary commercial buildings, grew 40%. It did so into a US market where non-residential construction spending fell 7% in nominal dollars over the first five months of 2026; the American Institute of Architects' forecast panel now expects a 0.3% decline for the full year, and about a 1% fall excluding data centers. Whatever is driving this corner of the heating and cooling business, it is not the building cycle.

Four sessions did all the damage

Eight listed companies carry the thermal load of the AI build — from cold plates inside the rack to the pipefitters who weld the central plant. As a group they are down about 6.8% over 30 days. Almost all of it arrived between 17 and 21 August, when the same eight fell 7.7% on an equal-weighted basis. Before that week nVent was up 9.7% on the month and EMCOR up 12.9%.

No member reported results in that window. What did happen is that the 30-year Treasury yield topped 5.33% on 18 August, a 19-year high, in a global bond selloff. The one name that rose was Ecolab, the water-treatment and cleaning-chemicals group, up 2.5% — and its cooling exposure is a $4.75bn purchase of CoolIT Systems that closed on 2 July, not a multi-year order book. Long-dated backlogs got marked down; a just-bought earnings stream did not. That is what a repricing of duration looks like, not a repricing of demand.

nVent built its growth rather than buying it

nVent Electric makes the enclosures, busbars and liquid-cooling hardware that sit inside and beside the rack. June-quarter revenue rose 52.8% to $1.47bn, of which 47 points were organic — the EPG acquisition added roughly seven. Its infrastructure vertical, overwhelmingly data centers, grew more than 100% organically and now accounts for close to 60% of first-half sales, against 12% when nVent was spun out. Operating margin widened 417 basis points to 20.4%.

Management guides to more than $2bn of data-center revenue this year on a $2.5bn backlog, and is building a third liquid-cooling plant in three years, 160,000 square feet, for early 2027. It is a challenger, not the incumbent: Vertiv holds over 11% of the liquid-cooling market and the top five vendors only about 35% between them. Ecolab's CoolIT now competes for the same socket. nVent costs 14.0x trailing gross profit, down from 16.6x in May while that gross profit grew 21.7% since February. The forward price/earnings ratio of 29.9x against 41.2x trailing, though, already assumes a 53% earnings jump — and consensus has growth halving in 2027.

EMCOR sells hours, and its order book is full

EMCOR Group is a labor business: 44,000 electricians and pipefitters installing central plant, high-purity piping and power distribution. Its remaining performance obligations hit a record $17.14bn at 30 June, up 43.9%, and 95% of that is organic. Bookings of roughly $6.7bn against $5.16bn of revenue imply a book-to-bill near 1.3. Network and communications led the increase — mechanical revenue in that category more than doubled — though institutional, healthcare and water work contributed materially too.

The mechanism is rack density. Management describes campus projects growing from 20 megawatts in 2019 to 100-200 megawatts now, with mechanical revenue per employee running up to twice the normal rate on AI jobs. Operating margin reached 10.6%, above the high-single-digit range EMCOR has historically earned — 6.96% in 2023, 9.84% last year — even as the mechanical segment gave back 110 basis points to 12.5% accepting guaranteed-maximum-price contracts. EMCOR costs 9.66x trailing gross profit against roughly 11.0x in both February and May, and against 20.2x for Comfort Systems, the closest listed comparable, which grew 50.3% on a richer 25.9% gross margin.

AAON's problem is real; the de-rating is twice its size

AAON's June revenue doubled to $627m and operating income nearly tripled. But gross margin fell 230 basis points to 24.3% and full-year gross-margin guidance was cut 200 basis points to 25-26%, sending the shares down 5.9% on the print. The cause is capacity: Memphis overhead ran $18.1m in the quarter against $3m a year earlier, while BasX's own segment gross margin improved to 30.0%. Free cash flow is negative on $102.6m of year-to-date capital spending. Total backlog is near $2.0bn but slipped sequentially as large engineered orders lumped. The market was entitled to price that. It priced considerably more: 25.8x trailing gross profit in May, 13.1x now — below February's 21.7x — with the last 9.3% arriving in a week that carried no AAON news at all.

The setup

Where it stands — Three accelerating businesses re-rated downward in one bond-market week, with only AAON carrying a disclosed margin deterioration.

Would confirm — EMCOR's September-quarter remaining performance obligations hold above $17bn with network and communications again the largest increment.

Would invalidate — nVent's 2026 data-center revenue guidance falls below $2bn, or AAON's BasX backlog declines year on year.

Watch next — Third-quarter results: EMCOR and nVent in late October, AAON in early November.

Valuation — EMCOR at 9.66x trailing gross profit versus 11.0x in May and 20.2x for Comfort Systems; nVent 14.0x, AAON 13.1x.