1. Jones WP. Air Conditioning Engineering. London: Edward Arnold, 1978. p. 380.
2. Clifford GE. Heating, Ventilating and Air-conditioning. Englewood Cliffs, NJ: Prentice-Hall, 1982.
3. Stoecker WF, Jones J. Refrigeration and Air Conditioning, 2nd edn. New York: McGraw-Hill, 1982. p. 103–110.
4. Annual Report. Jordan Engineering Association, 1992:76–79.
5. Ageing effect of polypropylene used in heating systems;Arafah;Journal of Radiation, Physics and Chemistry,1993