I watched the videos on hydronic heating, and found something that was not covered. There are apparently air issues with hydronic systems, when air is being trapped in the pipes. Could you please help me to clarify which device helps to get the air out? Could you please tell me what that device is and what is the symbol commonly used for it in the schematic diagrams?
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Hi @tatyana.swift and welcome to the Community!
Let’s get one of our expert architects to help clarify. @coachlizschneider do you mind helping Tatyana?
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@tatyana.swift You’re right having air trapped in a hydronic heating system can cause the system to become air-bound and non functional. In order to release any air in the system Air Vents are placed at all high points of the system, which is where these air pockets accumulate.
You can read more about hydronic heating systems in Mechanical and Electrical Equipment for Buildings by Stein et al. Chapter 9 “HVAC for Smaller Buildings”
To see the symbol used for air vents you can refer to page four of the pdf linked here: https://onlinelibrary.wiley.com/doi/pdf/10.1002/9781118403198.app2
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@coachlizschneider, thank you for looking into this and the explanation. I checked the chapter you referred to as well, very helpful, thank you! The pdf you attached did not seem to have a symbol for air vents, I found this one: 
do you think that is the correct symbol?
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@tatyana.swift I think that symbol would likely indicate an air vent. It is very similar to the manual air vent symbol from the link I shared:
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Thank you!
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hi I thought hydronic systems use a valve to release air?