The need to measure methane (CH₄) and carbon dioxide (CO₂) emissions from cattle in production environments is increasing. Previously, CH₄ and CO₂ emissions have been accurately measured for short-term repeated periods using a supplemental feeding station (GreenFeed, C-Lock Inc.). Considering the interest in residual feed intake, there is an opportunity to combine the measurement of feed intake with the measurement of CH₄, by incorporating this technology into a TMR-feeder. To do this effectively, it is necessary to design a feed bin that has desirable airflow characteristics, that ensure a high capture of emitted gasses and produces a fast response time to emitted gasses. The purpose of this study was to design a TMR feeder with optimal airflow characteristics. A TMR bin, 92 × 92 × 81 cm was constructed (dead-volume = 710 L). An opening for the cow’s head of 30 × 6 cm was made and the lid was sealed. Bin dimensions enabled adequate TMR to be offered, while allowing the cow to reach all corners. Airflow was extracted from the bin at a rate of 45 L/s using a fan. From the outlet gas, CO₂ concentrations were measured. Artificial smoke was used to visualize flow patterns inside the TMR bin and results were recorded on video. Separately, CO₂ gas was injected into the TMR bin at 7 g/min until the system reached equilibrium, at which point the CO₂ was removed. The T-90 equilibrium time of CO₂ disappearance was analyzed. Three gas extraction methods were tested: (m1) a 10-cm-diameter circular outlet, (m2) a manifold with 36 evenly spaced 1.27-cm-diameter holes in only the upper half of the bin, (m3) a manifold with 72 evenly spaced 1.27-cm- diameter holes throughout the bin. There was no observed sample loss from the head opening with any outlet configuration. However, m2 and m3 produced a significantly longer T-90 equilibrium time compared with m1 (24, 33, and 66 s, respectively). The multiple air outlets in m2 and m3 produced improved airflow characteristics. Although m3 produced the fastest equilibrium time, the air holes at the bottom of the bin could become plugged with TMR; therefore, manifold 2 is likely the optimal option. In conclusion, a well-designed TMR bin can produce acceptable airflow characteristics for the measurement of gaseous emissions from cattle while they are feeding.