I would like to use bus heat while on road.
The problem is, the scrol cage fan for the bus heater is too strong, almost like a tornado. Is there any easy solution to tame down the monster fan?
Try putting a speed control on the fan motor circuit, which would allow the fan to run at slower speeds when you do not need gale force hot air warming the entire coach in less than a nanosecond.
You can also change the fan blades to a set that push less air, but then when you need the speed, it will not be there.
See if you can find a voltage control circuit for the fan motor, to regulate its speed. That will keep you in the driver's seat, and not pinned to the back wall of the bus.
The OEM fans in my bus have big wire-wound resistors for the slower-speed settings. You could measure the current consumption of your fan and try to calculate what size resistor(s) you need, or just get hold of a bunch and experiment. I notice on mine that the manufacturer made a point of mounting the resistors directly in the air flow, which seems a sensible idea for keeping them cool.
Jeremy