It's not the appraised FMV that counts. It's the FMV of the house as if it was a rental.
Let's say that a fully furnished house in your neighborhood would rent for $1500 a month, and then you have $200 a month of utility bills. Then, as long as the housing allowance is less than $1700 a month, it would not be taxable. If it was more than $1700 a month, the amount over would be taxable.
If you need help determining the FMV as if it was a rental, you can check places like zillow, Craigslist, or ask a real estate agent for a quick estimate.
