boiler room

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An area, as in a building or on a ship, that houses one or more steam boilers or hot-water tanks.
• noun Informal A room equipped with telephones for making cold calls usually involving high-pressure or fraudulent sales pitches.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A room in a building that houses the boiler(s) and similar equipment.
• noun A compartment on a steamship that houses the boiler.
• noun informal A room full of telemarketers making cold calls.