Unless there are other circumstances for it, a commercial loan is typical for properties that are either used commercially, or are situated in a commercial zone/district, or may have been a commercial property at the time of acquisition, etc. Depending on the use and use code, you may be able to "replace" (refinance) a commercial loan with a lower interest rate residential loan -- if the house supports the loan to value ratio the bank wants to see, and if you qualify for the payments based on income and credit underwriting used in today's economy.
Check with a local agent, loan agent, or mortgage banker for more specific and precise clarifications on what you'll need to have ready to get this sort of evaluation under way. Good luck.
J. Mario Preza