Like Tvauri explains, these heat storage hypocausts rather common in 14th - 15th century Livonia — where the climate was much colder
compared to the Central and Western Europe — were born combining the
ancient method of heat storage (stones) used by the indigenous inhabitants of present day Finland, Estonia, and Latvia in their saunas for hundreds of years with the hypocaust
technology originating from Rome used by monks and religious orders.