OFTEC Flue Systems for Oil 3 — Questions and Answers
Question 1: What is the purpose of a draught stabiliser (diverter) on a conventional oil flue?
- To maintain consistent draught by allowing room air into the flue when draught is excessive (Correct answer)
- To block the flue when the burner is off
- To increase the draught during high winds
- To act as a spark arrestor
Correct answer: To maintain consistent draught by allowing room air into the flue when draught is excessive
A draught stabiliser has a weighted flap that opens when the flue draught exceeds the required level, admitting room air to dilute the flue gases and reduce the pull. This maintains stable burner operation regardless of wind conditions.
Question 2: Why is a condensing oil boiler's flue system different from a conventional oil boiler's flue?
- The flue gases are cooler and more acidic, requiring corrosion-resistant materials and a condensate drain (Correct answer)
- There is no difference in the flue system
- Condensing boilers do not need a flue
- The flue is larger to handle more gas volume
Correct answer: The flue gases are cooler and more acidic, requiring corrosion-resistant materials and a condensate drain
Condensing oil boilers produce cooler, wetter, and more acidic flue gases. The flue system must use corrosion-resistant materials (typically plastic or acid-resistant stainless steel) and include a condensate drain to handle the liquid produced.
Question 3: What should be checked during a visual inspection of an oil flue system?
- All joints for security and leaks, terminal condition, clearances to combustibles, and support brackets (Correct answer)
- Only the terminal at the top
- Only the connection at the boiler
- Only the flue pipe colour
Correct answer: All joints for security and leaks, terminal condition, clearances to combustibles, and support brackets
A thorough flue inspection covers: joint security and seal integrity, terminal condition and clearance, clearance from combustible materials (minimum 50mm), adequate support brackets, slope direction, and signs of corrosion or damage.
Question 4: What is the consequence of an undersized flue on an oil-fired appliance?
- Inadequate draught leading to combustion gas spillage into the room (Correct answer)
- The boiler runs more efficiently
- The oil consumption decreases
- The flue lasts longer
Correct answer: Inadequate draught leading to combustion gas spillage into the room
An undersized flue cannot handle the volume of combustion gases produced by the burner. This restricts flow, reduces draught, and can cause combustion products (including CO) to spill back into the room through the draught break or joints.
Question 5: What is the required clearance between a single-wall oil flue pipe and combustible materials?
- A minimum of 50mm clearance must be maintained (Correct answer)
- No clearance is required
- 25mm is sufficient
- The flue can touch combustible materials if insulated
Correct answer: A minimum of 50mm clearance must be maintained
Single-wall oil flue pipes must maintain at least 50mm clearance from any combustible material (timber, plastic, etc.). Where passing through a combustible floor or wall, a proprietary fire-stop spacer must be used.
Question 6: What test is used to confirm a flue is functioning correctly and not spilling combustion products?
- A smoke match or pellet test at the draught break while the burner is running (Correct answer)
- A water pressure test of the flue
- An electrical continuity test
- A sound test by tapping the flue pipe
Correct answer: A smoke match or pellet test at the draught break while the burner is running
A smoke match or smoke pellet held at the draught break (diverter) while the burner is operating shows whether combustion gases are being drawn up the flue. If smoke is pushed into the room, there is a dangerous spillage condition.
OFTEC Flue Systems for Oil 3
What is the purpose of a draught stabiliser (diverter) on a conventional oil flue?