So we've had a week or two of very cold temp's around here (5f at night, maybe a high of 10 or 12 f some days). Temps that in a "normal" winter we might see in late January. I've stuck a temp sensor in the center grill of the dashboard vent of my '300m and have the temp control set to "Hi" and the fan set to maybe 25% speed. I' have 3 readings so far, (outside temp / inside vent temp): 50/104 32/94.5 12/82.4 These are in (f). Inside temp is when engine has been up to full temp (as indicated by engine temp guage) for at least 20 minutes. 3 points, but very linear line. For every increase / decrease of 1 degree f of outside temp, there is a change of about .5 degree in the max heat that I get out of interior center vent. Interior air temp inside car is (I would guess) no colder than maybe 50f when these readings are made. Car is kept in heated garage overnight so the car interior temp is at least 50 - 55f when I start my short morning commute of about 5 - 10 minutes.