The term 'EXTREMELY HOT CHAMBER' can be summarized as a FURNACE, which is a seven-letter word. A FURNACE is a device used for heating and is usually fueled by gas, oil, electricity, or wood. It is typically found in homes and businesses to provide heat during cold weather. Furnaces are also used in industrial settings to heat materials to high temperatures, such as in the production of steel. In this case, the FURNACE is an extremely hot chamber, meaning it is capable of reaching very high temperatures.