If you use a MacBook or a MacBook Pro, then at some point of time while the machine was placed on your lap, or you were using a CPU intensive application, you must’ve felt the bottom of the case getting heated up, to a point where it becomes really uncomfortable keeping it on your lap, or in some rare cases, it may even leave burn marks on the surface where it is kept (a table for example). Mac OS X automatically pumps up the speed of your exhaust fan with an increase in CPU usage, but for normal usage, the fan runs at a default speed which is set by Apple to around 1500-2000 RPM, depending on the make or model of your MacBook.
smcFanControl is a small utility that lets you regulate the speed of your exhaust fan. It allows you to override this lower limit that is set by Apple. I use a MacBook White (Early 2008) model and the default lower limit for the fan speed set by Apple on my MacBook is 1800 RPM. I decided to test out how much effect the fan speed has on the CPU temperature.
smcFanControl allows you to setup profiles, which define the minimum speed of the exhaust fan. Two profiles are defined here –
Testing and Results
I first selected the ‘Default’ profile, and continued my work (I didn’t launch any new applications, just continued using the ones that were open, without putting much load on the already open ones). I tested this profile for about 10 minutes, and almost constantly, my CPU was running at 60 °C (values noted down using iStat Menus).
I then switched to the second profile, ‘Higher RPM’, and continued doing the same work, with the same applications open. Within a minute of switching to the ‘Higher RPM’ setting, the temperature went down by 3 degrees to 57 °C. After 10 minutes of running on this profile, the temperature went to a constant 55 °C.
The test was successful, and I could feel the temperature difference as the laptop was resting on my lap.
smcFanControl is a brilliant utility which can help you bring down the temperature of your MacBook in an effective manner. But it also takes care of safety. Even though it is theoretically possible to reduce the speed of your exhaust fan to 0 RPM, but that could result in your hardware getting damaged from overheating. Thus, smcFanControl does not allow you to choose a speed setting for your fan lower than the default limit set by Apple. That limit is defined by leftmost corner of the slider in the smcFanControl preferences. For my MacBook, this number was 1800 RPM. This safety feature prevents your hardware from getting damaged due to overheating.
Though I would like to keep my MacBook cool, but running your exhaust fan at a higher RPM comes at a cost which is battery life. If the fans are running faster, they will consume your battery faster. To help you out with power management, smcFanControl has features which will help you define profiles that will automatically be activated based on the power source and the status of the battery. I’ve setup the profiles and setting such that when my MacBook is running on battery, it will use the ‘Default’ profile, and while charging or running on AC power, it will use the ‘Higher RPM’ profile.