Since the days of the Roman Empire, hot water and hot gases have been circulated as heating media. Some time around 1920, a new concept in industrial and process heating was first successfully tested in Europe. In 1927, the first technical journals were written in the United States concerning high temperature liquid and hot water systems. Newer, stronger materials were developed, pressures and temperatures were increased, and by 1930, many 400°F (204°C) circulating systems were in operation in England.
These systems began to grow in the post-World War II days. Since then, these systems have operated extremely well, and most owners will attest to their satisfaction. Numerous systems have followed, proving that high temperature hot fluid for process heating is successful.