It seems most buildable structures act as if they have a fith of their heat capacity as one would calculate using the property tab.
This includes pipes and vents but excludes tiles.
Therefore buildings overheat faster and the heat exchange between pipes/vents and their content behaves differently than expected.
Steps to Reproduce
build room out of insulation, build structure, dump liquid with different temperature from structure, wait for equillibrium, math
This issue has not been confirmed by a developer yet.