Using A Fan To Dry Walls
This is a great idea for drying out your walls, but it
doesn't guarantee that there isn't any other damage underneath or in the
wall. The arrow is pointing to a large water damage stain that was
caused by a roof leak.
If you use a fan to dry the walls out from the water damage, and you start to smell a musty odor, within a few days, there's a good chance that you have mold or mildew growing somewhere.
If you can't see the mold and mildew, there's a good chance that it would be underneath the wood flooring, behind the water damaged drywall or even on the wood framing.
If you don't smell any odors, that doesn't mean that you don't have mold or mildew growing anywhere, but this could be a good sign. If the roof water leak is repaired and this never happens again, you might be in pretty good shape.
If the damage is a re-occurring, you could find yourself with some large home repair bills in the future. Remember to repair the water leak problem before repairing the water leak damage.
Home Repair Tip: It wouldn't be a bad idea to contact your local rental yard, to see if they have more water damage drying equipment that you could rent. It might cost you a few dollars now to dry out your home, but it could cost you a lot more in the future if you don't.
Fans are one of the best ways that I could think of for drying out your walls. The pros might not use a fan like the picture above, but they use fans to remove high levels of moisture from homes to prevent mold and mildew.