Abstract. Ammonia (NH 3 ) in broiler houses can degrade bird performance. Acidifier such as, sodium bisulfate (SBS) applied to litter inside broiler houses can reduce NH 3 release and thus improve bird performance. While there are multiple studies on acidifier effects on inside NH 3 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 2 , whole house), Medium (0.73 kg/m 2 , whole house), Low (0.49 kg/m 2 , whole house), and Control (0.49 kg/m 2 , brood chamber) on inside NH 3 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 3 concentrations were much higher in the cool-season versus warm-season flocks. Generally, higher acidifier application rates provided better NH 3 suppression. Ammonia concentrations were ≤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 3 concentrations were ≤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 3 concentrations of 3, 6, and 14 ppm, respectively, versus the Control treatment (24 ppm). For a 62-d flock, mid-house NH 3 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.