I'm assuming you are a sole proprietor farm business for these answers. If the house and farm have just one power meter, you must estimate what percentage the farm uses and deduct that amount. In most cases, I would not use the home office deduction for a farm. Most small farms use the cash accounting method. You can not deduct your personal use home mortgage as a farm expense, only the interest paid on farm land can be deducted. If they are on one loan, you must estimate the split by valuation on your real estate tax bill. Maintaining or repairing your personal use home is not a farm expense.
