.Langley, B. C. (1991). High-Efficiency gas furnace troubleshooting handbook. Prentice-hall, Inc.
Lua i Stíl Chicago (17ú heag.).Langley, Billy C. High-Efficiency Gas Furnace Troubleshooting Handbook. New jersey: Prentice-hall, Inc, 1991.
Lua MLA (9ú heag.).Langley, Billy C. High-Efficiency Gas Furnace Troubleshooting Handbook. Prentice-hall, Inc, 1991.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.