Through the last 7 years I have used three unibody 15" Macbook Pro's, with the Early 2015 Retina Model the latest. The evolution of the power saving through the models and case temperature decrease is tremendous. Taking into account that the latest model is even thinner and more powerful, this is a marvelous engineering application.
Macbooks of the last ten years (apart from the fanless 12" model) use fans that feed the hot air to the front of the case, towards the display. This is mandatory, as the logic board is found below the keyboard, and the battery is positioned below the trackpad, as shown in the teardown photo of iFixit.
All 15" models have tradionally used two fans, spinning at ~2000rpm when idle. The optimization level of the heat dissipation for the Retina model, is shown by using a 2160rpm when idle for the left fan and 2000rpm for the right fan. A thermal image of the heat dissipation is shown bellow. The temperature difference between the two fans is clearly shown.