Numerous innovations can be attributed to the Ancient Romans. Aqueducts, concrete, newspapers, even elevators—these are just a few of the technologies that have seeped into the Modern Age due to the accomplishments of the ancient civilization. Similarly, HVAC systems are often thought of as recent advancements, and they are in many ways, granting desired comfort and air quality in indoor environments. However, heating systems have likely origins in Ancient Rome.
The Romans used hypocausts in large bathhouses and some other public buildings, and they sometimes installed them in private residencies. A hypocaust consisted of a space beneath the floor, which was raised above the ground by pillars, or pilae, composed of brick, mortar, or concrete about two or three feet high.
A furnace, containing a continuously burning fire, produced heat, which would travel through the space beneath the raised floor. This heated the floor and therefore the rest of the room. Flues installed in the walls provided adequate circulation and allowed space for the cooled air to escape. In the bathhouses, the fire in the furnace also heated hot water.
To save space, the furnace of the hypocaust was generally given its own room, and it required continuous attention and labor. The flues were built directly into the walls to not occupy any useful space. From these different components, a hypocaust was essentially both a primary system and a secondary system, as it not only created heat, but distributed it as well.
This granted indoor comfort, and the hypocaust surely was standardized to a degree, with the ruins of the system having been discovered in cities throughout the expansive reach of the Roman Empire. However, a hypocaust’s usage didn’t always lead to peaceful warmth.
The most obvious threat was the possibility for the fires igniting the furnace to reach untamed levels, endangering life and property. Another danger was brought forth as the fumes given off by the fire would easily creep out into the holding space below the floor and into the primary heating space.
This generated the deadly gas we know today as carbon monoxide. And, considering that carbon monoxide wouldn’t be observed for well over a millennium, and the silent, odorless, and invisible killer wasn’t completely understood until the rise of chemistry in the Eighteenth Century, it is unlikely that the Romans frequenting bathhouses were truthfully familiar with this threat.
Ultimately, hypocausts surely would be in violation of today’s standards and codes, but they are still the earliest form of room heating.
Please note that the origin of hypocausts in Ancient Rome is debatable, as they may have also been utilized centuries before in Greece. In fact, the origin of the word hypocaust is the Late Latin word hypocaustum, which derives from the Greek hypokauston, literally meaning “heated from below.”
Today’s heating systems are far more advanced, and they are subject to standard practices developed by the collective knowledge of experts in the HVAC industry. Standards for heating, ventilation, and air conditioning are developed by the American Society for Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) and other standard developing organizations.