Which of the following is essential for the proper combustion of gas in a furnace?

The correct answer is air supply, which is essential for the proper combustion of gas in a furnace. Combustion is a chemical reaction that occurs when fuel (in this case, gas) reacts with oxygen from the air. For this reaction to be efficient and safe, a sufficient amount of air must be provided to ensure that there is enough oxygen available.

An adequate air supply allows the gas to combust completely, which helps in achieving proper flame efficiency and minimizes the production of harmful emissions, such as carbon monoxide. If the air supply is inadequate, it can lead to incomplete combustion, which poses risks of inefficiency and increased safety hazards due to the potential buildup of dangerous gases.

The other options do not play a crucial role in the combustion process as air supply does. While cool temperatures may affect the overall efficiency of heating systems, they do not directly contribute to the combustion process itself. Low pressure may affect gas delivery but is not a primary requirement for combustion. Similarly, excess fuel could lead to incomplete combustion and increased emissions, creating unsafe conditions rather than ensuring effective combustion.