Gas Fitter Practice Test

If 1 cubic foot of propane gas is 2500 Btuh, what is the ratio of combustion air?

1. 10

2. 25

3. 5

4. 30

The correct answer is: 25

To determine the ratio of combustion air based on the given propane gas information, we must consider the combustion process. Propane, a hydrocarbon gas, requires a certain amount of air to burn completely. The general rule of thumb for propane combustion is that it needs approximately 24 cubic feet of air for every cubic foot of propane burned. Given that 1 cubic foot of propane produces 2,500 Btuh (British thermal units per hour), we can ascertain the optimal combustion efficiency by comparing the air requirement to the propane usage. The ratio of combustion air is often expressed as parts of air to parts of gas. In this case, for 1 cubic foot of propane, the approximately calculated standard ratio of combustion air aligns with the answer option that indicates a ratio of 25, which represents 25 cubic feet of air for 1 cubic foot of propane. This understanding correlates with the typical requirements for propane combustion, reaffirming that the answer indicating a ratio of 25 is accurate for the combustion of propane gas at the specified energy content.