I have read in a local history book (mining towns in Colorado) that around 1900, those who put in steam heat were more likely to have bedbugs than those who kept their old coal stoves. The authors attributed this to increased humidity from the steam system, which the bedbugs apparently liked. I am a fiction writer, not a HVAC expert. But it seems to me that steam heating systems are enclosed, so that steam/humidity doesn't escape. Am I missing something? Were there differnt kinds of steam heat back then? I am trying to set up a fictional scene correctly. Thank you to anyone who can help!