The present invention utilizes radiation reflectors on the refractory wall of a fired furnace opposite the spaces between adjacent tubes. The refractory radiation reflectors have a base contiguous with the refractory surface and secured to a subjacent structure, and an isosceles triangular cross section with similar sides extending from the base. The base has a dimension less than the spaces between adjacent tubes to facilitate installation in a modular construction. The radiation reflectors focus the reflected radiation from the flame onto the dark side of the tubes. The invention increases the overall heat transfer of the tube by increasing the heat flux rate for the backside of the tube, and also decreases the flux and temperature differentials between the front and rear sides of the tubes.