<abstract><title><italic>Abstract. </italic></title> Ammonia (NH<sub>3</sub>) in broiler houses can degrade bird performance. Acidifier such as, sodium bisulfate (SBS) applied to litter inside broiler houses can reduce NH<sub>3</sub> release and thus improve bird performance. While there are multiple studies on acidifier effects on inside NH<sub>3</sub> concentrations in broiler houses, there are no studies in roaster houses where big broiler birds are grown for 8 to 12 wk. The impact of different SBS application rates - High (1.46 kg/m<sup>2</sup>, whole house), Medium (0.73 kg/m<sup>2</sup>, whole house), Low (0.49 kg/m<sup>2</sup>, whole house), and Control (0.49 kg/m<sup>2</sup>, brood chamber) on inside NH<sub>3</sub> concentrations was evaluated over six flocks of roaster chickens (~4 kg ea.). Ammonia concentrations were measured with acid scrubbers that sampled air at two locations (mid-house, end-house) 0.15 m above the litter. Inside NH<sub>3</sub> concentrations were much higher in the cool-season versus warm-season flocks. Generally, higher acidifier application rates provided better NH<sub>3</sub> suppression. Ammonia concentrations were â¤10 ppm during brooding, as well as for the entire duration of most warm-weather flocks with the High and Medium treatments. In the Low treatment, NH<sub>3</sub> concentrations were â¤25 ppm during brooding but approached or exceeded 25 ppm with the Control treatment. During brooding, the High, Medium, and Low treatments resulted in significantly lower mid-house NH<sub>3</sub> concentrations of 3, 6, and 14 ppm, respectively, versus the Control treatment (24 ppm). For a 62-d flock, mid-house NH<sub>3</sub> concentrations were significantly lower in the High and Medium treatments versus the Control treatment; concentrations in the High, Medium, and Low treatments were reduced by 47%, 32%, and 20%, respectively, versus the Control treatment.