A building , comprising an air-conditioning apparatus , an air conditioned space , and a non-air conditioned space that is not an air conditioned space , the air conditioning apparatus comprising: a heat medium relay unit including a heat exchanger related to heat medium that exchanges heat between a flammable refrigerant and a heat medium different from the refrigerant and including a housing of the heat medium relay unit , the heat medium relay unit to be disposed in the non-air conditioned space in the building ; a single or a plurality of outdoor units being connected to the heat medium relay unit by piping to circulate the refrigerant therein, the single or the plurality of outdoor units to be disposed in a space outside the building or a space inside the building that is not isolated completely from the space outside the building ; and a single or a plurality of indoor units being connected to the heat medium relay unit by piping , the single or the plurality of indoor units circulating the heat medium therein to exchange heat with air related to the air conditioned space , wherein at least the piping that is to be disposed in the space inside the building among the pipings in which the refrigerant flows is covered with a pipe shaft , characterized in that the non-air conditioned space is adapted to be ventilated to the space outside the building by free convection or forced convection, wherein the housing has a vent hole being formed to allow ventilation between an inside and an outside of a housing space, wherein ventilation between a space in the pipe shaft and the air conditioned space is not possible, and wherein ventilation from the non-air conditioned space to the air conditioned space is not possible or a ventilation resistance of a vent hole between the non-air conditioned space and the air conditioned space is set larger than a ventilation resistance of a vent hole between the non-air conditioned space and the space outside the building . a heat medium relay unit including a heat exchanger related to heat medium that exchanges heat between a flammable refrigerant and a heat medium different from the refrigerant and including a housing of the heat medium relay unit , the heat medium relay unit to be disposed in the non-air conditioned space in the building ; a single or a plurality of outdoor units being connected to the heat medium relay unit by piping to circulate the refrigerant therein, the single or the plurality of outdoor units to be disposed in a space outside the building or a space inside the building that is not isolated completely from the space outside the building ; and a single or a plurality of indoor units being connected to the heat medium relay unit by piping , the single or the plurality of indoor units circulating the heat medium therein to exchange heat with air related to the air conditioned space , wherein at least the piping that is to be disposed in the space inside the building among the pipings in which the refrigerant flows is covered with a pipe shaft , characterized in that the non-air conditioned space is adapted to be ventilated to the space outside the building by free convection or forced convection, wherein the housing has a vent hole being formed to allow ventilation between an inside and an outside of a housing space, wherein ventilation between a space in the pipe shaft and the air conditioned space is not possible, and wherein ventilation from the non-air conditioned space to the air conditioned space is not possible or a ventilation resistance of a vent hole between the non-air conditioned space and the air conditioned space is set larger than a ventilation resistance of a vent hole between the non-air conditioned space and the space outside the building . <EOS>