Since it's a rental the interest rates are about .500-.750% higher than owner occupied interest rates. I'd compare refinancing vs. just starting to make additional payments to principal in order to pay your mortgage down quicker.
Unfortunately the tax assessments are rarely accurate in giving you an appraised value... they are accurate giving you an assesed value, which your tax treasurer uses to calculate how much property taxes you owe, but not for appraisal purposes. Check your home out at
www.zillow.com to get a semi-accurate indicator of value.
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