Hi , and thanks for your post - you've asked a good question.
In general terms, dehumidifiers are used when the air is humid in one's home and the high humidity may be difficult for the person living there. In those situations, an air conditioner may be of help.
On the other hand, when one's environment is extremely dry, sometimes a humidifier can make all the difference.
This may be a topic you'd want to discuss with your physician. Your physician (and you), know your condition best. Between the two of you, I would think you'll be able to determine which device would be most appropriate for you to use. It may even depend on the season!!
What do you think?
All the best,
Leon (site moderator COPD.net)