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Quoted (Cut & paste) directly from From IRS Publication 936:"Qualified HomeFor 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." You might ask: What do they consider a "Second Home"? Here's the answer from the same publication:"Second home. A second home is a home that you choose to treat as your second home." It goes on to say:"Second home not rented out. If you have a second home that you do not hold out for rent or resale to others at any time during the year, you can treat it as a qualified home. You do not have to use the home during the year."Ain't the internet grand?