Not that I would ever own one, but all the American cars that I have been in direct ALL the air to the floor when you set their manual HVAC controls to the heater setting. Although you can leave them set on vent and all that hot air comes out at your face. I personally can't stand hot air blowing anywhere near my face. Both the Audi and BMW of family members work just as the Mercedes system, no heat from the center vent.

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'94 E320 with 272,000 miles. '92 500SEL 133,000 miles.
Mods to the '94: TomTom GPS in place of ash tray, Auto Dimming Mirror ,Memory seat, DEI 545T Auto lamps, DEI 530T Auto Up/Down Windows, DEI Remote Start, Motorola Bluetooth® Car Kit, Built in phone charger using factory phone wiring, RainTracker Rain sensing wiper, Keyless Entry, Ambient lighting of center storage compartment. Soon: factory heated seats, REST
Mercedes-Benz is my addiction of choice.
http://www.youtube.com/vanwiek