To support @Hal_Al 's answer:
From IRS Publication 527, page 19:
"If you use a dwelling unit as a home and you rent it less than 15 days during the year, its primary function isn’t considered to be a rental and it shouldn’t be reported on Schedule E (Form 1040). You aren’t required to report the rental income and rental expenses from this activity. Any expenses related to the home, such as mortgage interest, property taxes, and any qualified casualty loss, will be reported as normally allowed on Schedule A (Form 1040)."
A day rented below FMV is not a rental day.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
