While the construction of a slab on ground floor should not be difficult, the contractor must pay special attention to every aspect of the job. And one of the most important of these is the selection of a suitable heating system For most low cost, single story homes the warm air system will present the best combination of economy and satisfaction. The warm air is forced through the system of radial ducts to registers near the outside walls of the rooms. Use a pipe that is light and strong and can be laid directly on grade. The down-flow furnace can be installed directly on the floor slab over a plenum or distribution box cast in place. A simple box form should be used to cast the plenum. Ducts are butted roughly against the form; they can be held in place by means of nails driven into the form but kept withing the inside of the duct. The top of all ducting should be 4 inches below the finished floor level. Ducts should slope downward about 4 inches from register to plenum. After being given their desired grade and location the lengths of duct should be supported at suitable intervals by a rough haunch of concrete while base course and slab are being placed. Taping al all joints with good quality adhesive tape should be used by all joints should be sufficiently tight that dirt will be excluded after the tape has rotted. Placing the supporting haunches under the joints is one way of avoiding this latter danger.