The energy crisis has led humankind to drastically think about optimization of facilities which are in closed connection with energy resources. Therefore, optimization of thermal systems from heat transfer point of view, to decrease heat losses and therefore energy consumption, is an explicit goal in the field of thermal sciences. This work is about conjugate radiation and convection heat transfer in a cylindrical enclosure using two radiation shields, to decrease heat loss. The experimental study applies three different materials, namely aluminum, copper and steel, as radiation shields. Numerical investigation is performed and validated against experimental data, using three-dimensional finite volume method. Different positions for radiation shields within the enclosure are considered. Both experimental and modeling studies adopt two different enclosure pressures, i.e., 0.2 and 1.0 atm. The inner cylinder is assumed to have two different temperatures, i.e., 473 K and 673 K. Seventy six different experiments are carried out to capture the best heat reduction with different radiation shield materials, inner cylinder temperatures, enclosure pressures and radii for radiation shields. Results show that both enclosure pressure and radiation shield emissivity are responsible for reduction of the total heat loss from the inner cylinder. (C) 2015 Elsevier Ltd. All rights reserved.