1. Kirov, D. (2012). Heat holding. Technica, Sofia. ISBN-978-954-03-0701-5, №17992; (Kirov, 2012)
2. Kostov, P. (2004). Heat- and mass transfer. Sliven.
3. Krastev, Zh., Markov, V., & Chotorov, D. (1987). Technical thermodynamics and heat transfer. Technica, Sofia. UC-536(075.8), №13737.
4. Stamov, S., Sendov, S., Nachev, N., Markov, A., Stoichkov, N., Kirii, A., Carlson, V., & Kirov, D. (1990). Guidebook of Heating, ventilation and air conditioning. Part I. Fundamentals of heating and ventilation. Technica, Sofia. UC 697:828.8, №16001.
5. Stamov, S., Aleksiev, N., Shushulov, K., Kirov, D., Zhechkov, N., Kadiiski, S., Kamburov, K., & Stankov, A. (2010). Guidebook of Heating, ventilation and air conditioning. Part II. Heating, heat- and gas supply. Technica, Sofia. ISBN-965-03-0601-9(part.2).