[wapakfred]

What might happen if that venting will allow the unit to move more air. That may well overload the motor and burn it out. You can test this with an amp meter if you want to stay with that unit. Read the amps and compare the reading the FLA number on the motor plate. In all honesty, I would be surprised if your happy with the performance of that unit. The reducer for the exhaust can be as simple as a piece of plywood cut to fit the DC outlet, then put a 4" (+/-) hole in it to accept a PVC union, secure it with screws and seal it, then pipe your pipe into it.

 

[wapakfred]

Any thing that reduces the resistance to flow in a DC system will increase the amount of air that system can move…..hence reducing the back pressure on the discharge allows more air movement. That (more air), in turn, increases the load on the motor. Like I said, you can test this easily. You will see an increase amperage with an open discharge, it may not be enough to be a problem…but then again it might.

 

[wapakfred]

You couldn't be more wrong, but I'll leave it at that. You are correct that running it with no load is just fine, now adding air to the impeller adds load, hence more amps as the motor tries to overcome that load (and stay at it's stated RPM). Reducing backpressure at the discharge allows it to add air (and load). But with that, I'm done…..