In a properly designed system, heat controls for each room may be used to adjust the temperature in each room, meaning the air heats up that room, satisfying the thermostat and turning off the call to the central system. The "excess" air pressure should be shunted away, not just trying to blow past the registers in the unheated rooms. Logically, if fewer rooms are "calling" for heat, the furnace won't be on as much.
Similarly, if my house has 11 baseboard heating zones, it takes a lot less power to heat only two zones than all 11. Of course, none of them would be set "dangerously low", so as to be anywhere near the freezing point.