I have a circular fan that works really good when the grates are unblocked. Normally I take the grates off the box fans and clean them with soap and water and then dry them and put them back on.
This fan is not like the box fans, and the grates cannot be taken off, or at least I have not found a way yet. I tried everything to get debris and hair and such out of the grates, and the only thing that works, for me, is to use a wire dog brush to get the dust and debris in the grates. Now the fan works great. I was so happy to find that this was successful, since I had tried everything from toothbrushes to wet cloths.
Everyone enjoy your summer of 2017 and try to stay cool!