Mass. Gen. Laws ch. 236 § 18
If a judgment creditor requires an execution to be levied on property which is claimed by the debtor to be as a homestead exempt from such levy and if the officer holding such execution is of the opinion that the premises are of greater value than an amount equal to either the automatic homestead exemption or the declared homestead exemption, as applicable, as defined in section 1 of chapter 188, appraisers shall be appointed to appraise the property in the manner provided by section 6. If in the judgment of the appraisers the premises are of greater value than the amount of either the automatic homestead exemption or the declared homestead exemption, as applicable, the appraisers shall set off to the judgment debtor so much of the premises, including the dwelling house, in whole or in part, as shall appear to them to be of the value of the amount of the exemption and the residue of the property shall be levied upon and disposed of in like manner as land not exempt from levy on execution; provided, however, that if the property levied on is subject to a mortgage, it may be set off or sold subject to the mortgage and to the estate of homestead in the same manner as land subject to a mortgage only.
Mass. Gen. Laws ch. 236, § 18