"I figure that at lower speeds, the air spends more time in the heater core, and gets hotter, so that makes up for the fact that there is less hot air. "
Yes, and no. Yes the air gets hotter at slower velocities. And no it doesn't make up for it. While the air coming out will be significantly hotter, you still get the most heat by having the max blower speed. Max blower speed forces more cold air into the heater which extracts more heat from the heater core.
Any auto with automatic heat starts the blower on low speed when the water hits about 110 degrees. This gets heat into the car as soon as possible, but at lower volumes. On mine, it steps up again at about 125 and again at about 150.
In any case, there is only so much heat available at a given temperature of the heating coil. Lower speeds give a higher relative air temperature due to the increased residence time, but overall heat output would be less than the optimal combination of coil temperature and air flow.
Have something to add? Share your thoughts — no account required.
Ask the community — no account required