From: Rabbi Moshe Sofer
To: Rabbi Yaakov Baruch Frenkel
A homeowner has a heated mikveh pit in a room of his house, covered with boards when not in use, and asks whether Torah study is permitted there. The Chasam Sofer permits it, ruling that while heated mikveh water itself may carry bathhouse status, the surrounding room is a separate domain that remains clean and free of steam when covered, and recommends a movable partition as an added measure of piety.
Source: Shu"t Chasam Sofer OC §18