An infinitely long furnace of $0.5\:m\times 0. 4 \:m$ cross-section is shown in the figure below. Consider all surfaces of the furnace to be black. The top and bottom walls are maintained at temperature $T_1=T_3=927^\circ C$ while the side walls are at temperature $T_2=T_4=527^\circ C$. The view factor, $F_{1-2}$ is $0.26$. The net radiation heat loss or gain on side $1$ is_________ $W/m$. Stefan-Boltzmann constant = $5.67 \times 10^{-8}$ $W/m^2-K^4$
