that question for me is so hard, so I put in three of them just to cover my self. But the main thing to do is exhaust the air in the TT. if you suck you get all the hot air off the outside roof and put it back into the TT and defeat the fan's purpose. Just open a window here and there and let the fan pull in cool air. If you put it in the bathroom be sure you turn it off before you flush the toilet since it will draw the odor from the black tank into the TT and that is another thing you don't want to put up with. they sure do draw the moist air fromthe shower and leave the mirror clear for the shaving part of the morning ritual.
