My understanding of a boiler system is that it is closed, meaning the water stays in the pipes and constantly recirculates. However, there is a vent (3" PVC pipe) that is connected to it that periodically blows steam. Where does this steam come from?
Water – Why does the boiler vent steam
boilerexhaust-venthot-watersteam
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Best Answer
You appear to have (based on your other questions) a high efficiency gas boiler which is venting combustion products at relatively low temperature via PVC pipe.
Combustion products are carbon dioxide and water vapor (and carbon monoxide if combustion is incomplete) - thus "steam" (condensate) will be present in the exhaust.