For masonry fireplace openings that are 6 square feet or larger, the hearth extension must extend at least _____ inches in front of and _____ inches beyond each side of the fireplace opening.

The correct answer is based on building codes and standards that dictate the safety and functionality of masonry fireplaces. For masonry fireplace openings that are 6 square feet or larger, the hearth extension is required to provide adequate protection against the heat and potential embers that may escape from the fireplace during use. The extension must enhance safety by minimizing the risks of fire hazards to the surrounding area.

The requirement for the hearth extension to extend at least 20 inches in front of the fireplace opening provides enough distance for users to safely approach the fire without risk of burns. Additionally, the 12 inches required on each side of the fireplace opening ensures that any potential embers or ash that might fall out while the fireplace is being used are contained on the hearth, preventing them from igniting nearby surfaces.

This answer aligns with safety practices and building regulations intended to protect structures and occupants from the effects of fire. The dimensions specified are designed to effectively mitigate any hazards associated with using larger masonry fireplaces.