Improvements relating to downhole heater assemblies and methods of operating such

The present invention relates to a downhole heater assembly comprising at least one heating tool with a delivery support connection point, by which the heating tool is connectable to delivery means via a delivery support such that said heating tool can be delivered to and retrieved from a downhole target region of a borehole. The assembly is provided with a baffle that is configured to be positionable in the borehole at a location between said heater tool and said delivery means. When in position said baffle acts to restrict the movement of heated fluids produced during the operation of the heating tool so as to at least partially replicate the fluid flow conditions found in the test vessel in which the heating tool's configuration was originally tested. The present invention also provides associated methods that employ a baffle between a heating tool and the above ground delivery means used to deploy the heating tool downhole.