Though many notebooks remain cool to the touch, others can feel like the steering wheel of a car that’s been parked in the sun for a few hours. We’ve recently tested some pretty warm machines, such as the HP Envy 15, which had a palm rest that reached a toasty 103 degrees during testing. The exhaust vent of our Toshiba Satellite T135D review unit measured a sweltering 125 degrees, and the 101-degree touchpad was too hot for comfort. So what exactly causes a notebook to get so warm? And what can manufacturers—and you—do to beat the heat?
Consequences of a Hot Notebook
A poorly cooled notebook is extremely uncomfortable to use. In fact, though heat-related injuries are rare, some systems actually carry warning labels. For example, many current Toshiba Satellites have stickers affixed to their bottoms which state: “Caution: PC base can become hot! Avoid prolonged contact to prevent heat injury to skin.”
Aside from burns, laptop heat is suspected as a risk factor for male infertility. A 2005 study conducted by a group of doctors at SUNY Stony Brook showed that male scrotal temperatures rose significantly—potentially killing or damaging sperm—after subjects used notebook computers for 60 minutes. Though the group concluded that just sitting with with one’s legs close together also can raise scrotal temperature, the damage potential was much greater with a computer on one’s lap actively emitting heat. Suzanne Kavic, MD, Loyola University’s director of reproductive endocrinology and infertility, noted that there’s not enough evidence to say how much, if any, notebook use would render a man infertile, but that the less heat a notebook emits, the better. “If you have a cooler running laptop, that can only help,” she said.
A notebook that gets too hot on the inside can also suffer component damage or reduced performance. “There’s a certain point in a system where they’ll get so hot that rather than melt down, the processor itself is designed to throttle,” said Matt Kohut, worldwide competitive analyst for Lenovo. “So rather than 2.2 GHz, it will run at 1.8 or 1.6 [GHz]. It will slow itself down, generating less heat. The problem is that you don’t get what you paid for.”
Causes of Heat
While the CPU is responsible for much of a given system’s heat, other factors come into play. “Hotter than the average processor are discrete graphics chips,” said Kohut. “That’s going to be the hottest part of your system.” Other warm components include memory, voltage regulators, and wireless cards.
The amount of heat given off by a component will be the same no matter what notebook it’s used in. The differences from notebook to notebook, however, are based on air and heat flow within the system, the amount of power consumed, and notebook chassis material. While notebooks made from sleek-looking aluminum and other metals are increasingly popular, such systems tend to feel hotter. That’s because of differences in thermo-mechanical properties of the materials, according to Rajiv Mongia, principal engineer for Intel’s Thermal Technologies team. For example, an aluminum chassis will feel hotter to the touch than a plastic chassis of the same temperature.
“The aluminum chassis stores more heat by virtue of its thermal conductivity, its specific heat, and its density,” Mongia said. “So when you touch this aluminum, your hand reaches a temperature closer to that of the aluminum because of this thermal conductivity and the thermal density of the material.”
Manufacturers can cool aluminum skins with good air flow designs and by covering the exterior with less conductive materials. Unfortunately, some poorly cooled systems may rely on the metal surface to help dissipate heat that would otherwise harm internal components.
“A lot of vendors are essentially using their cases as giant heat sinks, which then go to your lap,” Lenovo’s Kohut said. “But when that metal gets hot to the touch, that’s unacceptable.”