Abstract: The present room heater includes a housing supporting internal electric heat sources. The housing surrounds the heat sources with an interconnected serial series of chambers made from heat-conducting material. Air is motivated by an electric fan through the series of chambers to effect stepped uniform heating, as well as optimal heating as the air moves through preheat chambers and then closely past the heat sources to an outlet opening. The chambers are made using modular and relatively simply-made components that interfit to form the chambers, such that multiple configurations are possible, including stacked and laterally-adjacent versions. The modular components include a flat part, hat-shaped part, and U-shaped part that interfit to define a first elongated chamber and a second elongated chamber that wraps onto three sides of the first elongated chamber, the hat-shaped part having end-located notches to permit flow of air between the chambers.