Outlet termination

Flue terminations for gas in domestic situations are governed by BS5440-1 Section 4.2. The figure below illustrates recommendations for the most common terminations.

Adjacent taller structures may require increased height. The minimum flue projection through the roof is 600mm to the underside of the terminal.

Flue routing

Systems should be vertical as far as possible for most efficient evacuation and should not exceed 45° from the vertical,otherwise resistance to flue gas flow will result. Bends should be kept to a minimum and a vertical rise of 600mm minimum should be allowed for immediately above the appliance.

As a general rule, the vertical distance (A) between the appliance and the flue terminal should always be at least twice the horizontal distance (B) between the appliance and the terminal (see FigB).

The B Vent range includes 0° - 90° fully adjustable bends which can be used where the flue system needs to be offset e.g. to avoid trusses and terminate to a ridge terminal. These bends can be rotated 360° after the angle has been set to achieve the correct direction of flue parts.

Air Supply

Provision for ventilation to supply air to the appliance must be arranged in accordance with the appliance manufacturers instructions.This is necessary to ensure correct and safe operation of the appliance and to ensure correct venting and avoid spillage of flue gases.

Use of B Vent on condensing appliances

B Vent is not suitable for this application. Prima Plus and ICS Plusare the products in the Rite-Vent range specifically designed for condensing applications.

Termination beside existing chimney pots

A commonly encountered situation is the need to site the termination of a gas appliance amongst chimney pots on an existing stack. The termination should be made such that the bottom of the terminal is at the same level as the top of the surrounding pots. This is to ensure maintenance of suitable draught conditions. Schiedel Rite-Vent supply a British Gas approved Terminal extension kit for this purpose.

Use of K Vent to combat condensation

With the advent of high efficiency gas appliances,which have generally lower flue temperatures, condensation problems can arise where the system is exposed to extreme conditions of cold, particularly external runs and ventilated roof spaces of modern properties.

K Vent, which interconnects directly with B Vent can help overcome this problem and maintain the efficiency of the flue. With its stainless steel liner and high quality insulated cavity, K Vent assists the speedy evacuation of flue gases with minimum heat loss. This maintains flue gas temperature, reducing the formation of condensation and produces a more efficient system. The stainless steel liner helps resist the corrosive effect of any condensation which may still form.

Compliance with BS5440-1:2000.5.1.7

BS5440-1:2000.5.1.7 requires the use of stainless steel insulated flue on all exterior gas flues greater than 3 metres.

K Vent, having a stainless steel liner and Superwool™ insulation is interchangeable with B Vent and should be used for exterior installations. See the K Vent brochure for more information.