Greetings! I am not an engineer but my guess would be yes alittle, but not enough to notice. The same reason a vehicale uses more gas when the ac is on. When the ac is on it is harder for motor to run. It has less power and the idle air control motor bumps up the idle therefore uses more gas. just like towing something. the this takes horse power away from the motor. Well when the heater blower is on high, it draws current from the batt. This needs to be replaced otherweis your batt will lose charge and the car will die. So the alt charges more and is harder to spin when under a load than when not charging therefore using more gas