Lua APA (7ú heag.)

.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.

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