CCP Chimney Draft & Combustion Principles Flashcards

What phenomenon occurs when wind creates positive pressure at the top of a chimney, preventing draft?

Answer: Wind-induced downdraft

Wind blowing across or down a chimney top can create positive pressure that opposes natural draft, causing downdraft or backdraft conditions.

How does the 'stack effect' in a tightly built building affect chimney performance?

Answer: It can compete with chimney draft and draw air in through the flue

In tight, well-insulated buildings, the stack effect can draw air in through the chimney rather than allowing combustion gases to exit, competing with or reversing draft.

What is the purpose of a barometric damper on an oil-fired appliance?

Answer: To regulate and stabilize draft by admitting dilution air

A barometric damper maintains consistent draft by opening to admit dilution air when draft is excessive and closing when draft is insufficient.

Which factor most significantly reduces chimney draft during warm weather?

Answer: Reduced temperature differential between flue gases and outside air

Warm weather reduces the temperature differential between hot flue gases and outside air, weakening the buoyancy-driven pressure difference that creates draft.

What does a draft gauge reading of zero indicate?

Answer: No pressure difference between the flue and outside atmosphere

A draft gauge reading of zero indicates no pressure differential between the flue interior and outside atmosphere, meaning no natural draft is present.

What chimney height above the roofline does NFPA 211 require for most residential installations?

Answer: At least 2 feet above any portion of the roof within 10 feet

NFPA 211 requires chimneys to extend at least 2 feet above any portion of the building or obstruction within 10 feet to ensure proper draft clearance.