Renting at below fair market, is considered personal use. If a taxpayer has any personal use of a dwelling that they rent, they must divide their expenses between rental use and personal use. They must divide expenses even if the dwelling doesn’t meet the definition of a residence. They may deduct only rental expenses on Schedule E (Form 1040). They may be able to deduct some of their personal expenses on Schedule A (Form 1040) if they itemize deductions.

Here is link for irs information:

https://www.irs.gov/newsroom/know-the-tax-facts-about-renting-out-residential-property