System Design

Outlet Siting

Flue terminations for solid fuel & oil are subject to BS7566 Parts 1, 2,3 and 4. Figure A illustrates recommendations for the most commonly encountered siting situations. Flue terminations for gas in domestic situations are governed by the new BS5440-1 2000 Section4.2. Figure B illustrates recommendations for the most common siting situations encountered. Adjacent taller structures may require increased height. The minimum flue projection through the roof is 600mm to the underside of the terminal.

Flue Routing

The chimney should remain as straight as possible through its vertical run to assist flow. Should it be necessary to offset a chimney run the following guidelines should be adhered to:

Gas: An offset no greater than 45° to the vertical, with a run between the bends (B) not exceeding half the overall height of the chimney (A) should be maintained See Figure C.

Oil - Solid Fuel: An offset no greater than 30° to the vertical, with a run between the bends not exceeding 20% of the overall height of the chimney should be maintained.

In both instances a maximum of two bends in any one chimney run should be used. A vertical rise of 600mm should be allowed immediately above the appliance before any offsets. Reference for both guidelines can be found in the Building Regulations Doc J and relevant British Standards on installations.

Terminal Types

For solid fuel appliances, BS7566 Parts 1, 2, 3 and 4 recommends use of an open terminal for chimneys up to 200mm diameter. Rain ingress should not be significant, but drain components can be fitted. Above 200mm a covered terminal can be used, and for all oil and gas installations. Mesh carries the risk of sooting and requires regular cleaning to avoid blockage particularly with oil and solid fuel.

Provision for sweeping, cleaning and maintenance

Provision should be made for inspecting and cleaning the chimney. This is particularly important on solid fuel applications. It is recommended that chimneys serving solid fuel appliances be swept as frequently as necessary but at least twice a year. Choose an access component suitable for your installation unless cleaning/inspection can be done through the appliance.

Room Ventilation

The room carrying the appliance should have an air vent either direct to an external air source or vented into a room that has an external vent direct to an air source. This is required to provide adequate air supply to allow the appliance and flue to operate efficiently. These requirements are specified in the Building Regulations (Document J) also by CIBSE and BS5440.

Commercial Installations

Schiedel Rite Vent can provide a full design & flue sizing advice service for commercial installations. The ICS range contains all the required components for commercial use including time-saving telescopic header tees for increasingly popular multi-boiler installations.

Provision for condensate disposal (subject to appliance manufacturer recommendations)

Normally solid fuel and atmospheric gas and oil appliances will not need a drain unless rain ingress is significant. Most condensing appliances however need provision for drainage. As a rule of thumb a condensing boiler produces 1 to 1.5 litres of condensate per hour per 10kw of input. This is a significant amount of acidic liquid which must be drained from the system. Choose appropriate flue drainage components, normally fitted at the base of the stack and close to the appliance outlet. A 5° slope on horizontal runs is advised, using the appropriate 85° or 40° bend and 95° tee.