Sony's VP of mechanical design, Yasuhiro Ootori, has said, "there is no difference in the cooling performance between vertical and horizontal installation" of the PS5.
In a translation on Reddit from a recent interview with Japanese site 4Gamer.net, Ootori addresses a question regarding whether the position of the PS5 will have any effect on the cooling system's performance.
"This is a frequently asked question. From the designer's point of view, there is no difference in cooling performance between vertical and horizontal installation," Ootori says. "I think some people think that the heat dissipation efficiency should be higher in the vertical installation due to the chimney effect. However, in a cooling system with an active fan (electric fan), the chimney effect is at the measurement error level. It works according to the specifications in both horizontal and vertical installation. Personally, I like the vertical placement where the top and bottom of the "PS logo" can be seen correctly."
In a recent PS5 teardown video featuring Ootori, it demonstrates how you can remove the vertical base of the console by way of a screw fixing it in place. The base can also be switched around to support the console horizontally, so you can place your PS5 in either position.
The cooling system also had an effect on the PS5 design, with the fans factoring into the size of the hardware. The same interview with 4Gamer.net also revealed that the PS5 cooling fans will get online updates for optimization, so the cooling system will adjust to the demands of which game you're playing over time.