Renewable natural gas (RNG), produced from biogas upgrading, is an important alternative to fossil fuels. Unfortunately, RNG contains several trace contaminants, one being NH3, of particular concern for RNG produced from farming operations. The presence of NH3 in RNG, particularly if it is injected into the natural gas (NG) pipeline network, could have serious consequences, ranging from damage to the NG infrastructure, to corrosion of the end-user equipment, and increased pollutant formation during combustion. This paper is part of a broader investigation studying all such impacts, the focus here being pollutant emissions. Two common end-user equipment were tested: An internal combustion engine and a household water heater, both operating with NG injected with NH3 with concentrations ranging from 0 to 500 ppmv. Emissions studied included unburned hydrocarbons (UHC), CO, and nitrogen oxides (NOx), the latter being of key concern. The presence of NH3 resulted in increased NOx emissions for both equipment. For the water heater, the relationship between the amount of NOx formed and the NH3 concentration was quantitative: For every molecule of NH3 fed to the water heater, one molecule of NO3 was additionally produced. However, for the engine a lower quantity of NOx was formed, to that corresponding to complete conversion. The results with both devices are significant, indicating the need for thorough RNG purification prior to its injection into the NG network.