Blower motor died on a 18 year old Furnace: Update 2

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wrote:

How does this apply to auto heaters?
You're the first person I've seen mention that one can get iiuyouc, almost the same result with lower velocity and higher temp.
I like to put my car fan on one of the lower two speeds, because it makes too much noise in the higher two.
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.
Am I right, and do you have a guess about how much heat speed 2 puts out compared to speed 3? It's a Chrysler at the moment.

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"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.
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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.
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