Gas Fitter Practice Test

If 1 cubic foot of natural gas is 1000 Btuh, what is the ratio of combustion air?

1. 10

2. 15

3. 5

4. 30

The correct answer is: 10

To determine the proper ratio of combustion air when burning natural gas, it's important to understand the basic combustion principles. The combustion of natural gas primarily uses methane, which requires a specific amount of oxygen to completely combust into carbon dioxide and water. When we consider that 1 cubic foot of natural gas generates 1000 Btuh (British Thermal Units per hour), the general rule of thumb for natural gas combustion is that it requires approximately 10 cubic feet of air for every cubic foot of natural gas burned. This translates to a combustion air-to-fuel gas ratio of 10:1. This ratio ensures that there is enough oxygen available to support effective combustion, preventing incomplete burning and ensuring efficiency. Utilizing this correct ratio also reduces the risk of byproducts like carbon monoxide, which is a colorless, odorless gas that can be hazardous. Thus, a ratio of 10 cubic feet of combustion air to 1 cubic foot of natural gas is widely accepted and represents the correct answer in this context.