This work evaluates a simple method to measure ammonia concentration average for building emissions measurements, using a low-cost system (Portable Monitoring Unit, PMU). The method is compared to a more sophisticated (Mobile Air Emission Monitoring Unit, MAEMU) as a standard. The research was conducted in two similar broiler houses in western Kentucky, USA. Four PMU monitors were randomly assigned to three locations in each broiler house in which simultaneous MAEMU measurements were being conducted as part of a year-long ammonia emissions project. The PMUs were configured to record data every 30s. Samples were taken from within the house for six minutes, followed by a fourteen-minute purge with outside air. Three different methods for computing 60-minute averages of ammonia concentration were evaluated based on the concentration readings taken from the PMU, considering that final concentration value and sampling intervals directly affect the computation of ammonia emission. The methods studied were denoted AVE2, AVE4 and MAX. The AVE2 method used values from the last two minutes of the sampling period, excluding the last value, whereas the AVE4 method used values from the middle four minutes of the sampling period, and the MAX method used the maximum concentration value over the sampling period. The MAEMU system obtained more frequent and accurate concentration and ER measurements (six to thirty measurements per location per hour). The three methods showed values very close to the standard results, and the method AVE 4 seems to be the more similar with MAEMU. The average differences between PMU AVE4 method and MAEMU are -1.06 ppm and -0.052 g/hr for NH3 concentration and emission rate, respectively, considering 20-minute averages. Results demonstrate the importance of careful selection of representative concentration readings when fans are operating, and the significant impact that different ventilation regimes can have on the accuracy.