Increasing the amount of excess air in a heating system will result in what effect on efficiency?

Increasing the amount of excess air in a heating system leads to decreased efficiency because it causes the combustion process to be less optimal. Efficiency in a heating system is about achieving the right balance of fuel-to-air ratio for complete combustion. When too much air is introduced, it can cool the combustion gases, leading to a lower stack temperature and a loss of usable heat.

The result is that while there may be more complete combustion of the fuel, the heat energy that could have been used for heating will be lost as it goes up the stack. This wasted energy contributes to lower overall system efficiency, making it essential to maintain the correct amount of combustion air for optimal performance and energy use.