What is typically the major cause of furnace inefficiency on very cold nights?

The major cause of furnace inefficiency on very cold nights is often linked to the incorrect heat anticipator setting. The heat anticipator is a small device within the thermostat that helps regulate the temperature by predicting when the furnace should turn off based on the current room temperature and the temperature setting on the thermostat. If this setting is not calibrated properly, the furnace may cycle on and off too frequently, resulting in uneven heating and increased energy consumption.

On very cold nights, when the demand for heat is high, an incorrect setting can lead to the furnace working harder than necessary to maintain the desired temperature, reducing its efficiency. This not only affects the comfort level in the home but can also increase utility costs due to the excessive operation of the heating system.

While other factors like insufficient gas supply, improper venting, and pilot light malfunction can contribute to overall furnace performance issues, they are less likely to be the primary cause of inefficiency specifically on very cold nights compared to the impact of an improperly adjusted heat anticipator.