Does a dehumidifier installed in a crawlspace to improve energy use qualify for tax deduction?

[Rav101]

Meant to say "tax credit" not deduction.

[Opus 17]

No.  

The instructions for form 5695 specify which types of equipment are eligible, 

https://www.irs.gov/instructions/i5695

A crawlspace dehumidifier actually increases energy usage, but improves comfort, and prevents structural damage due to moisture issues.  You may be told by the contractor that you will save energy because your AC has to run less to make the house comfortable -- I'm not convinced this is true, but even if it is, the relationship is too indirect to qualify.

If the dehumidifier is energy star rated, some states may have rebates or other programs, but the federal government does not.