From the view of environmental protection against the use of fossil fuels, a great number of efforts have been exerted to find an alternative energy source. Hydrogen may become an alternative. However, the only product species of the hydrogen flame is H2O, which emits only nonluminous radiation, so the radiation from a hydrogen flame is much smaller than that for a hydrocarbon flame. The authors designed and fabricated a laboratory-scale test furnace to study thermal characteristics of a hydrogen-air diffusion flame. In addition, the effects of addition of reacting as well as nonreacting solid particles were experimentally investigated. Among the total heat flux to the wall, about 75% was occupied by radiation while 25% was occupied by convection. When the aluminum oxide (Al2O3) particles were added, the radiative heat flux was reduced due to heat blockage effects. On the other hand, the total heat flux was increased when the carbon particles were seeded, because the overall temperature increased. The effects of swirl and excess air ratio were also examined. Additionally, a numerical simulation was carried out to simulate a hydrogen-air diffusion flame and was compared with the experimental results.