Please refer to IRS Publication 936 , Home Mortgage Interest Deduction - http://www.irs.gov/pub/irs-pdf/p936.pdf
You can deduct home mortgage interest if all the following conditions are met.
You file Form 1040 and itemize deductions on Schedule A (Form 1040).
You are legally liable for the loan.
There is a true debtor-creditor relationship between you and the lender.
The mortgage is a secured debt on a qualified home in which you have an ownership interest. "Secured debt" and "qualified home" are explained later.
For you to take a home mortgage interest deduction, your debt must be secured by a qualified home. This means your main home or your second home. A home includes a house, condominium, cooperative, mobile home, house trailer, boat, or similar property that has sleeping, cooking, and toilet facilities.
The interest you pay on a mortgage on a home other than your main or second home may be deductible if the proceeds of the loan were used for business, investment, or other deductible purposes. Otherwise, it is considered personal interest and is not deductible.
Main home. You can have only one main home at any one time. This is the home where you ordinarily live most of the time.
Second home. A second home is a home that you choose to treat as your second home.
More than one second home. If you have more than one second home, you can treat only one as the qualified second home during any year.
There is no requirements to have a main home in order to claim mortgage interest deduction for a second home. You may claim mortgage interest deduction for the second home even if you do not own a main home.