How were traditional hamams heated?
Historic baths used furnace-based heating systems to warm water and spaces. The exact system varies, and a working bath may use modern equipment today.

Related questions
What is the heated marble platform called?
It is called the göbek taşı. It is the central marble platform used within the bathing ritual; the exact treatment sequence depends on your package.
What happens on a first Turkish bath visit?
Usually you check in, change, warm up, receive the booked scrub and foam treatment, rinse and rest. Oil massage is a separate stage when included.
Does a hamam detox the body or treat illness?
Do not choose a hamam on promises of detoxification, weight loss or disease treatment. Treat it as a bathing experience; personal health suitability requires individual medical advice.