Gas Fitter Practice Test 2025 - Free Gas Fitter Practice Questions and Study Guide

To determine the required rough opening for a grill that is rated at 75% free area when you need a 50 square inch air supply opening, the calculation hinges on understanding how free area percentages affect the overall size needed.

In this scenario, if the grill has a free area of 75%, it means that only 75% of the grill’s total area actually allows air to pass through. To find out the total area of the opening needed, you would divide the desired free area by the free area percentage.

In this case, to find the rough opening, you would perform the following calculation:

1. Desired free area = 50 square inches

2. Free area percentage = 75% or 0.75

3. Total area required = Desired free area / Free area percentage

= 50 square inches / 0.75

= 66.67 square inches

Since rough openings are typically expressed in rounded terms, the total area rounds to 66.6 square inches.

This means the rough opening of approximately 66.6 square inches is correct to ensure that the grill operates efficiently and provides the necessary airflow for the system it supports.