Raising the temp on liquid cooling
Nvidia CEO Jensen Huang announced early this year that the new Vera Rubin processor, which is twice as powerful as the previous Grace Blackwell chip, doesn’t require its cooling water to be at a very cold temperature. In fact, the Vera Rubin can be cooled with water that’s 45 degrees Celsius, which is 113 degrees Fahrenheit. That’s hotter than the recommended settings for a hot tub. And it’s one degree hotter than the peak summer temperature in Las Vegas in 2025.
“With 45 degrees Celsius, no water chillers are necessary for data centers,” Huang said in his keynote address at the Consumer Electronics Show. “We’re basically cooling this supercomputer with hot water. It’s so incredibly efficient.”
The core benefit of using higher water temperatures is that it fundamentally changes how much mechanical cooling data centers have to use, says Alex Cordovil, research director at Dell’Oro Group. “As supply water temperatures move to 38 degrees Celsius and above, operators can dramatically expand the number of hours where they rely on economization,” he says.
In many climates, free coolers can handle much more of the work, with traditional chillers either downsized or used only during peak usage times. “That translates directly into lower energy consumption,” Cordovil says.
## Liquid cooling minus the chillers
Liquid cooling for data centers is nothing new. IBM was using water cooling for its System/360 mainframes back in the 1960s.
Even hot-water cooling has been around for many years. In 2012, for example, IBM announced the world’s first commercially available hot-water-cooled supercomputer, capable of handling temperatures as high as 45 degrees Celsius (113 Fahrenheit), just like Vera Rubin. In the winter, the hot water was used to heat the buildings in the Leibniz Supercomputing Center campus, saving $1.25 million a year.
IBM isn’t the only one.
“We’ve been doing liquid cooling since 2012 on our supercomputers,” says Scott Tease, vice president and general manager of AI and high-performance computing at Lenovo’s infrastructure solutions group. “And we’ve been improving it ever since—we’re now on the sixth generation of that technology.”
And the liquid Lenovo uses in its Neptune liquid cooling solution is warm water. Or, more precisely, hot water: 45 degrees Celsius. And when the water leaves the servers, it’s even hotter, Tease says. “I don’t have to chill that water, even if I’m in a hot climate,” he says. Even at high temperatures, the water still provides enough cooling to the chips that it has real value.
“Generally, a data center will use evaporation to chill water down,” Tease adds. “Since we don’t have to chill the water, we don’t have to use evaporation. That’s huge amounts of savings on the water. For us, it’s almost like a perfect solution. It delivers the highest performance possible, the highest density possible, the lowest power consumption. So, it’s the most sustainable solution possible.”
So, how is the water cooled down? It gets piped up to the roof, Tease says, where there are giant radiators with massive amounts of surface area. The heat radiates away, and then all the water flows right back to the servers again.
Though not always. The hot water can also be used to, say, heat campus or community swimming pools. “We have data centers in the Nordics who are giving the heat to the local communities’ water systems,” Tease says.
## Hot goes mainstream
While the technology has been around for years, it’s only lately, with the push for more AI compute, that hot-water cooling is moving into the spotlight—and into the mainstream.
“It’s now imperative,” says Arthur Hu, senior vice president, global CIO, and chief delivery and technology officer at Lenovo’s services and solutions group. And the AI factory that Nvidia’s Huang talked about is only possible with hot-water cooling.
Hu said that data centers deploying hot-water cooling usually do it in brand-new facilities. It’s possible to do it for just a part of a data center or a rack, he says, but it’s not usually a good fit because of power requirements.
“When you’re doing it at scale, the issue has to do with power density,” he says. “With the next generation, we’re starting to get into power densities that are 20 to 30 times higher. So, it doesn’t make sense to just use it in a corner of a traditional facility because they won’t have the power.”
According to the Uptime Institute, top-of-the-line processors can now be effectively cooled at 40 degrees Celsius, and now more direct liquid cooling providers are stepping up.
Data center cooling vendor Accelsius, for example, has a two-phase system that uses a dielectric liquid with a low boiling point to cool servers instead of water. “We perform six to eight degrees better than single-phase water,” says Accelsius CTO Rich Bonner. “You might be able to run at 51 to 55 degrees Celsius, enabling even greater energy efficiencies.”
One challenge of running at 45 degrees is that it’s in the microbial growth range, he says. “When you get to 55, 60 degrees Celsius, you’re hot enough that it kills all of that, ” he says. Plus, with water, there are corrosion issues, he adds.
The way that the two-phase systems work is that the fluid is pumped to the chip, where it starts to boil because of its lower boiling temperature. The bubbling creates turbulence, which increases heat transfer, making the entire system more efficient than water.
“We use four- to nine-times less liquid flow rate to the chip,” says Bonner. The trick is that the vapor isn’t any hotter than the liquid was—the heat goes into the phase change, not into making the liquid hotter. So instead of cooling down the fluid once it leaves the server, it’s condensed back to a liquid state.
Several other vendors are also in the game:
* In mid-2024, LiquidStack announced the availability of its CDU-1MW coolant distribution unit, which supports temperatures of up to 45 degrees Celsius.
* SuperMicro announced in early 2025 that its direct liquid cooling solution would now support temperatures of up to 45 degrees Celsius.
* Vertiv’s CoolLoop Trim Cooler, announced last March, supports water temperatures up to 40 degrees Celsius and cold plates of 45 degrees Celsius.
* Schneider Electric’s Motivair also supports liquid cooling of 45 degrees Celsius, and even higher.
## The benefits of liquid cooling
AI factories can draw hundreds of megawatts of power, but 30% of it is lost to power conversion, distribution, and cooling, according to Nvidia. At a temperature of 45 degrees, data centers can cool their water with just ambient air, compared to 35-degree alternatives, which can be more costly and complex.
According to McKinsey, liquid-cooling systems can have higher upfront costs but save money in the long term. Direct-to-chip cooling systems, for example, use 31% less power, McKinsey says, than traditional air.
Break-even points for liquid cooling systems are between one and three years, depending on local electricity costs.
Liquid cooling systems are also quieter, take up less physical space, and allow for higher server densities in data centers.
Higher temperatures also allow for closed-loop systems. Instead of cooling down water by letting it evaporate, the water can flow through a set of radiator pipes on the roof of the data center, dissipating just enough heat into the air to become useful again—even in warm climates. This significantly reduces a data center’s water consumption.
According to research released by Dell’Oro Group, the liquid cooling market nearly doubled in 2025, reaching close to $3 billion in revenue, and will grow to nearly $7 billion by 2029.
Air cooling remains predominant, but liquid cooling is gaining ground, according to a survey conducted by S&P Global Market Intelligence 451 Research. Today, 45% of data centers are only cooled by air, down from 48% in 2024. Meanwhile, 42% of respondents say they’re using a combination of air and liquid cooling, and 12% are fully liquid cooled.
In addition, 59% of respondents say they plan to implement liquid cooling in the next five years, with 21% intending to do so in the next 12 months.
The majority of respondents said that the benefit of liquid cooling is that it allows for increased server power and higher rack density. Other benefits cited include better power usage, better total cost of ownership, and quieter operations.
But there are downsides as well.
According to the S&P survey, there are reasons not to rush to upgrade. For example, the high cost of installation and maintenance was cited by 56% of respondents as a barrier to adoption. In addition, 53% say that air cooling is still adequate for most cooling needs. There’s also a lack of standardization for connecting components, say 29%, and 29% also cited a shortage of skilled personnel.
## Hot liquid’s downsides
So liquid cooling in general isn’t a magic bullet for data centers. And that is even more true for liquids at 45 degrees Celsius and above.
“There are no downsides in terms of ultimate performance and sustainability,” says Accelsius’ Bonner. “But there are challenges.”
For example, if all the water in a facility is at 45 degrees Celsius (113 Fahrenheit) then the whole data center is going to be at that temperature. “That can be very hot for operators,” he says. “You might need to cool the air just for the people to work in it.”
Surfaces can be hot to the touch, Bonner says. And just because the latest chips can run at high temperatures and be liquid cooled, that doesn’t mean the same holds true for all the other equipment in the data center. Finally, all those radiators on the roof can take up space. A lot of space, he says.
As a result, Bonner says, most hyperscalers and other large operators still have chillers in their data centers and are running their water at between 30 and 35 degrees Celsius.
After Huang’s CES keynote address, shares of several cooling technology companies immediately fell, according to Morningstar, impacting Johnson Controls, Modine Manufacturing, Trane Technologies, and Carrier Global. But they recovered quickly.
“It’s great that Nvidia is putting this out there, and I suspect that there will be takers,” Bonner says. “There is a trend where the temperature is going upward over time. Every generation, there’s a couple of degrees increase.”
Today, only a minority of data center workloads use high water temperatures in their water-cooled racks, says Dell’Oro’s Cordovil, and that’s mostly for AI workloads. “But we expect them to be the majority for liquid-cooled racks from 2027,” he adds.