Every house has different problems. Ventilation problems are a major issue for homes, especially older homes, and making the problem worse is that sometimes they are hard to get to, especially if they are under the home. A crawl space ventilation service can help with these problems.
Crawl spaces require a different set of solutions. They are a tight space requiring its own tools. Also, the animals that can be found under a house need to be dealt with, especially snakes and spiders.
It can be dirty work, and the tight spaces do not endear them to most HVAC specialists; as such few of them are willing to deal with the extra issues. However, finding a company that deals with crawlspaces is well worth the research, especially when you develop a problem and the only way of dealing with it is by sending someone underneath the home.