How were Roman steam baths warmed?
Check this site. Look for "hypocaust."
http://www.vroma.org/~bmcmanus/baths.html
Roman steam baths, also known as thermas or thermae, were warmed using a heating system called a hypocaust. The hypocaust was an intricate network of tunnels and pillars that supplied heated air to the floors and walls of the bathhouse. Here's a step-by-step explanation of how Roman steam baths were warmed:
1. Building Design: Roman steam baths were designed with an underfloor space, called the suspensura, which created a void beneath the bathhouse floor. This void allowed for the circulation of hot air.
2. Stoked Furnaces: Furnaces, called praefurnia or fornices, were built outside the bathhouse. These furnaces were stoked with wood or other fuels to generate heat. The design varied depending on the size and layout of the bathhouse.
3. Underground Channels: A network of underground channels, called flues, connected the furnaces to the hypocaust system within the bathhouse. These channels carried the hot air and smoke from the furnaces into the bathhouse.
4. Raised Pillars: Inside the bathhouse, a series of raised pillars, called pilae, were constructed to support the bathhouse floor. These pillars created a space for the hot air to flow.
5. Tiled Flooring: The bathhouse floor was constructed using hollow terracotta or ceramic tiles, known as tegulae and lateras. These tiles had gaps between them, allowing the hot air to rise through the pilae and heat the floors.
6. Radiant Heat: The heated air from the furnaces would circulate through the underground channels, rise through the pilae, and warm the bathhouse floor. This provided radiant heat that would warm the entire bathhouse, including the steam rooms.
7. Ventilation: To ensure proper air circulation, the bathhouses incorporated ventilation ducts, called suspensurae, which allowed cooler air to enter the bathhouse while the hot air was expelled through vents or chimneys.
By using this hypocaust system, Romans were able to create a warm and comfortable environment for steam baths, allowing them to enjoy the therapeutic benefits of sweating and relaxation.