Strong temperature mixing in subsonic air turbulence is studied in an open‐circuit wind tunnel with a 0.5 m cross section. The specially constructed heating grid consumes up to 300 kW of electric power at a mean flow velocity of 11 m/sec. The highest mean absolute temperature⟨T⟩reaches 370°K, while the rms temperature fluctuation&thgr;′at midtunnel is typically 6°K. Basic statistics of the temperature field are measured and discussed. It is found, in particular, that (i) the streamwise decay of the normalized mean‐square temperature fluctuation(&thgr;′ / < T >)2is not sensitive to the applied heating rates, suggesting that so far buoyancy contributes little to the dynamics of the turbulence; (ii) the observed decay rates are much higher than those reported by others in the literature and are consistent with the higher drag characteristics of the present grid; (iii) the temperature fluctuation spectrum, when normalized by local fluid properties and dissipation rates, retains a universal form and show an inertial‐convection subrange of limited extent; (iv) the one‐dimensional universal scalar inertial Kolmogoroff constant,&bgr;1, determined from such subrange has a value of 0.60±0.06.