First, take a straight edge and place it across the top of both pulleys to ensure proper alignment. The best way to check tension is to own a belt tension tool along with a belt tension guide. These are available at order houses such as Grainger or houses that specialize in bearings and belts like Standard Bearings. A good automotive store might also have them on hand or be able to order them for you.
If a centrifugal fan belts are loose, they will not always emit the typical loose belt squeal. On start up, especially on a dryer with a soft starter, you will hear the RPMs vary instead of hearing a smooth ramp up of RPMs. With a tri-start system, the sound might sound like a distant jet engine as each motor comes up to full speed. Another indicator of loose belts is decreased capacity.