Thermal expansion accommodation for circulated fluid systems used to heat subsurface formations

A system for accommodating thermal expansion of a heater in a formation, comprising:

• a conduit configured to apply heat to the formation when a heat transfer fluid flows through the conduit;
• and
• a movable wheel, wherein at least part of an end portion of the conduit is wound around the movable wheel, the movable wheel being movable at least in a vertical plane while the end portion of the conduit is wound around the movable wheel, and wherein the movable wheel is configured to move at least in the vertical plane to maintain substantially constant tension on the end portion of the conduit to absorb expansion of the conduit when the heat transfer fluid flows through the conduit.