Abstract: A domestic sewage system discharges hot sewage from several sources in a building such as a home to a sewer. The home is here provided with a fan in the sewer vent to draw air from an air inlet in the sewer, through the sewer where the air becomes heated, and then through a heat exchanger where heat is removed from the air such as for room or water heating, and then out through the sewer vent.

Abstract: A panel building component for use in conjunction with a heat-insulating wall of the type having a porous layer through which a transverse air flow is maintained in a direction opposite to the direction of the temperature gradient. The panel building component comprises a frame and two spaced layers secured to the frame and defining an air space between them. One layer is rigid and impermeable to air flow whereas the other layer has a limited permeability to air flow. The panel building component is mounted as a lining or cladding on the wall with the air-permeable layer in face-to-face engagement with the porous layer of the wall. The air space is adapted to be connected to a fan for maintaining a reduced pressure in the air space to cause external air to flow through the porous layer into the air space.