Flue Systems for Oil Flashcards

What is a twin-wall insulated flue system and when is it typically used?

Answer: A double-walled flue with insulation between the walls, used for external or exposed runs

Twin-wall insulated flue comprises an inner and outer pipe with insulation between them. It is used for external installations or internal runs through unheated spaces. The insulation maintains flue gas temperature, preventing excessive condensation and maintaining draught.

What is the minimum terminal height above ground level for a horizontal balanced flue on an oil appliance?

Answer: 600mm above ground level

A balanced flue terminal must be at least 600mm above ground level or any surface where a person might stand. This prevents interference with the air intake, contamination from ground-level debris, and prevents people from being directly exposed to flue gases.

Why must an oil flue pipe slope upward away from the appliance?

Answer: To ensure condensation flows back toward the appliance's condensate trap rather than pooling

Sloping the flue upward (minimum 1 in 12) away from the appliance ensures condensation drains back to the appliance where it can be safely dealt with by the condensate trap. Pooling condensate in the flue causes corrosion and blockage.

What is the maximum number of 90-degree bends typically allowed in a domestic oil flue system?

Answer: Two 90-degree bends (or equivalent 45-degree bends)

Most manufacturer instructions and Building Regulations limit the flue to two 90-degree bends (or their equivalent in 45-degree bends). Each bend reduces available draught and increases resistance to gas flow. Two 45-degree bends equal one 90-degree bend.

What happens if a conventional oil flue does not have adequate ventilation air supply to the room?

Answer: The burner starves for air, causing incomplete combustion and potential CO production

Conventional (open) flue oil appliances draw combustion air from the room. Without adequate ventilation (permanent air vents), the room becomes depleted of oxygen, causing incomplete combustion, CO production, and potential flue gas spillage.

What size permanent air vent is typically required for a conventional flue oil boiler?

Answer: 550mm² per kW of rated input over 5kW

For conventional flue oil appliances, a permanent air vent of 550mm² per kW of rated input above 5kW net is typically required. This ensures adequate combustion air supply. The vent must be non-closable and positioned to avoid draughts.