What factor primarily affects gas input ratings at higher altitudes?

The primary factor that affects gas input ratings at higher altitudes is atmospheric pressure. As altitude increases, atmospheric pressure decreases, which can influence the performance of gas appliances. Gas burners are designed to operate under certain pressure conditions, and at higher altitudes, the reduced atmospheric pressure means there is less oxygen available for combustion.

This change in pressure can lead to incomplete combustion, which may result in lower efficiency and potential safety issues. Therefore, appliances often require adjustments or recalibration to function effectively at higher altitudes to ensure they continue to operate safely and efficiently.

While humidity levels, temperature, and wind speed can have various effects on overall combustion processes and the environment, they do not have as direct an impact on gas input ratings compared to atmospheric pressure.