A shut room at the bottom of a building where the heat is made. It is hot, loud and crowded with , the door is usually locked, and the people upstairs never see inside — they only feel the result.
From the picture
一整間都在打推銷電話的辦公室
這是教學上的聯想，不是這個詞歷史來源的說明。可以想成：那種辦公室又擠又熱，電話聲一直響，整個房間像鍋爐一樣在燒；而且跟真的鍋爐房一樣，它藏在別人看不到的地方，外面的人只接到結果——一通電話。
noun · C1
A room or office where people spend the day phoning strangers and pushing them to buy shares or services, using heavy pressure and sometimes lies. The word is also used for the whole operation, not only the room. Mainly American English, informal.
電話高壓推銷據點
noun · B1
The room in a large building, or the space low down inside a ship, that holds the boiler together with the pipes and machines that heat the place or drive it.
鍋爐房