CCS CCS Hearth & Firebox Components 1 — Questions and Answers
Question 1: What is the function of the smoke shelf in a fireplace firebox?
- To support the weight of the flue liner
- To catch falling debris and deflect cold downdrafts away from the fire (Correct answer)
- To hold the grate above the firebox floor
- To provide a sealed surface for the damper plate
Correct answer: To catch falling debris and deflect cold downdrafts away from the fire
The smoke shelf sits behind the damper and catches falling soot, rain, and debris while deflecting cold downdrafts upward so they don't push smoke into the room.
Question 2: What is the correct term for the angled rear wall of a firebox that helps direct smoke upward into the smoke chamber?
- The fireback (Correct answer)
- The corbel
- The witches oven
- The smoke baffle
Correct answer: The fireback
The fireback is the angled or sloped rear wall of the firebox, designed to radiate heat into the room and direct combustion gases upward toward the smoke chamber.
Question 3: Firebox walls must be built using which type of brick to withstand high combustion temperatures?
- Standard facing brick
- Firebrick (refractory brick) (Correct answer)
- Cinder block
- Concrete masonry units
Correct answer: Firebrick (refractory brick)
Firebrick is made from refractory clay that withstands the extreme temperatures of combustion without cracking or spalling unlike standard brick.
Question 4: What mortar must be used to repoint or repair firebox firebrick joints?
- Type S Portland mortar
- Refractory (high-temperature) mortar (Correct answer)
- Type N mortar
- Premixed tile grout
Correct answer: Refractory (high-temperature) mortar
Refractory mortar is rated to withstand firebox temperatures; standard mortars will crack and crumble under the same heat conditions.
Question 5: What is the minimum recommended firebox depth from the front opening to the rear wall according to NFPA 211?
- 8 inches
- 12 inches (Correct answer)
- 20 inches
- 36 inches
Correct answer: 12 inches
NFPA 211 requires a minimum firebox depth of 12 inches to allow safe combustion and proper upward draft toward the smoke chamber.
Question 6: Which component sits directly above the firebox opening and forms the bottom boundary of the smoke chamber?
- The lintel
- The throat damper (Correct answer)
- The hearth extension
- The smoke shelf
Correct answer: The throat damper
The throat damper is positioned at the top of the firebox opening, controlling the passage of air and smoke up into the smoke chamber.
CCS CCS Hearth & Firebox Components 1
What is the function of the smoke shelf in a fireplace firebox?