Glossary
Flue terms explained.
The words on drawings, quotes and site, in plain English. For site managers, estimators and anyone new to flues.
A
Appliance
The boiler, generator, water heater, oven or other plant that makes the flue gases or exhaust. The flue is designed around it.
Guide: what we need to price your jobB
Back pressure
Resistance to flow in an exhaust or flue, felt at the appliance outlet. Engine and burner makers set the most their equipment can take, and the system is sized to stay under it.
Generator exhausts and silencersBuilding control
The local authority or private body that checks building work meets the Building Regulations. For a flue they may ask for the calculations and drawings. We provide those; the customer or their consultant submits.
Design and calculationsC
Canopy
A hood over an appliance or process that catches heat, fumes or steam before a fan extracts it.
Canopies, fans and ductworkCascade
Several boilers or water heaters joined to one shared flue, usually firing in turn to match demand.
Boiler fluesCCTV survey
A camera run through a flue or chimney to record its condition inside, often from the top down. Shows cracks, blockages, failed joints and debris.
Testing, inspection and surveysCertificate of conformity
A document issued at the end of a job confirming the system was installed as designed and tested. Issued where it applies to the job.
Guide: the paperwork at the endChimney
A structure that holds one or more flues and carries the gases above the roof. Large or industrial ones are often called stacks.
Chimneys and linersChimney height approval
For some larger combustion plant, the local authority must approve the chimney height before it is built. It is based on a height calculation for the plant.
Design and calculationsCHP
Combined heat and power. An engine that makes electricity and recovers its heat for the building. Its exhaust is treated much like a generator exhaust.
Generator exhausts and silencersClearance to combustibles
The gap a flue must keep from timber and other materials that can burn. It depends on the flue type and its temperature rating, and is shown in the product data.
Boiler fluesCombustion air
The air an appliance needs to burn its fuel. It comes from the room, through plantroom ventilation, or through a duct from outside on room-sealed appliances.
Design and calculationsCondensate drain
A drain point that collects water forming inside a flue and takes it through a trap to a drain, so it does not run back into the appliance or sit in the flue.
Boiler fluesCondensing boiler
A boiler that takes extra heat out of its flue gases, cooling them until water condenses. Its flue runs cooler and wetter, so materials, seals and falls are chosen for that.
Boiler fluesCone joint
A joint where the tapered ends of two sections fit together and are pulled tight with a clamp band. Quick to assemble and common on insulated exhaust systems.
Generator exhausts and silencersD
Downdraught
Wind, or air moving round nearby buildings, pushing flue gases back down the flue. Terminal position and height help avoid it.
Design and calculationsDraught
The natural pull of hot gases rising up a flue, which draws the flue gases out of the appliance. It depends on height, temperature and how much the flue resists flow.
Guide: can my old chimney be used?E
Expansion bellows
A flexible section that lets a hot flue or exhaust grow and shrink as it heats and cools, without stressing the joints or supports. Common on generator exhausts.
Generator exhausts and silencersF
Fire stopping
Sealing round a flue where it passes through a fire-rated wall or floor, so the fire separation is kept. Usually a fire-rated sleeve or collar.
Boiler fluesFlanged joint
A joint where two sections end in flat rings (flanges) bolted together with a gasket between. Strong and gas tight, so it suits larger exhausts and industrial stacks.
Industrial chimneys and stacksFlue
The pipe or duct that carries the products of combustion from an appliance to outside.
Boiler fluesFlue calculation
The sums that set a flue's size, height and route so the gases leave safely at the right pressure. They use appliance data such as output, gas flow and temperature.
Design and calculationsFlue fan
A fan fitted to a flue to pull the gases through when natural draught is not enough, for example on a long or low route.
Canopies, fans and ductworkFlue liner
A new pipe, often flexible stainless steel, run down inside an existing chimney so it can serve a modern appliance safely.
Guide: can my old chimney be used?Free-standing stack
A chimney on its own base that carries its own weight and wind load without being tied to a building.
Industrial chimneys and stacksG
Generator exhaust
The pipework that takes exhaust gases from a generator or engine to outside, usually with one or more silencers.
Generator exhausts and silencersH
Handover pack
The documents sent at the end of a job: completion report, photos, test reports, drawings and the O&M manual.
Guide: the paperwork at the endHeader
A horizontal flue that collects the gases from several appliances and carries them to one riser.
Boiler fluesI
Inspection door
A removable door or section in a flue that lets an engineer look inside and clean it.
Service and maintenanceIsometric drawing
A 3D-style drawing of the flue route that shows every length, bend and fitting on one sheet.
Design and calculationsK
kW and kVA
Units for the size of an appliance. Boilers are usually rated in kW of heat; generators in kVA of electrical output. Both help size the flue.
Guide: what we need to price your jobM
Mast
A steel structure that a tall flue or stack is fixed to for support above a roof or beside a building.
Steelwork and supportsMEWP
Mobile elevating work platform. A scissor lift, boom lift or similar used to work safely at height.
How we workO
O&M manual
The operation and maintenance manual: what was installed, the drawings, test results, product data and how to look after it.
Guide: the paperwork at the endP
Plume
The visible cloud from a flue terminal, mostly water vapour from condensing boilers in cold weather. Where it drifts matters near windows, vents and walkways.
Design and calculationsPositive pressure flue
A flue where the gases inside are at a higher pressure than the room, usually pushed by the appliance fan. Every joint must be sealed so gases cannot leak out.
Boiler fluesPressure test
A test where the flue or exhaust is sealed and put under pressure to check the joints for leaks. The result goes in a test report.
Testing, inspection and surveysProcess exhaust
Extract from industrial processes such as ovens, furnaces, kilns and dryers, taken safely to outside.
Process exhaustR
Rain cap
A cap on top of a flue that keeps rain out while letting the gases escape. Some appliances need an open terminal instead, so it is chosen per job.
Boiler fluesRAMS
Risk assessment and method statement. Sets out the hazards on a job, how they are controlled and the step-by-step method. Written for the actual site.
How we workRiser
The vertical part of a flue that carries the gases up through or outside the building.
Boiler fluesRoof flashing
The weatherproof plate or collar where a flue passes through a roof, sealed to the roof covering.
Boiler fluesRoom-sealed appliance
An appliance that takes its combustion air from outside through its own duct, rather than from the room it sits in.
Boiler fluesS
Seal
The ring in a flue joint, often called a gasket, that makes it gas tight. Its material is chosen for the flue temperature and for wet or dry conditions.
Boiler fluesSilencer
A unit in an engine or generator exhaust that cuts noise. Sized to the engine and to the noise limit for the site. Some jobs use two in series.
Generator exhausts and silencersSingle wall flue
A flue with one skin of stainless steel and no insulation. It gets hot to the touch, so where it can run depends on access and clearances. Also used as a liner.
Boiler fluesSite survey
A visit to measure, sketch and photograph the flue route, check any existing chimney and plan access before the design is finished.
Guide: what happens on a flue surveySmoke test
A test where smoke is put into a flue to show any leaks and check the gases go where they should.
Testing, inspection and surveysSpigot
The outlet on the appliance that the flue connects to. Its size is one of the first things needed to price a flue.
Guide: what we need to price your jobStorm collar
A collar fitted round the flue just above the roof flashing that throws rain clear of the gap between them.
Boiler fluesSupport band
A clamp that goes round the flue and fixes it to a wall, frame or steel. Spaced along the run to hold it in line.
Steelwork and supportsT
Technical submittal
The pack sent for approval before work starts: drawings, calculations, product data and method.
Design and calculationsTerminal
The fitting at the very end of a flue, where the gases leave. Its type and position help them disperse.
Boiler fluesTermination height
How high the flue outlet sits above the roof and in relation to nearby buildings, windows and air inlets. Set by calculation and the rules for the appliance.
Design and calculationsTest point
A small sealed port in a flue where an engineer can insert a probe to measure flue gas, temperature or pressure.
Testing, inspection and surveysTwin wall flue
A flue with inner and outer stainless steel skins and insulation between. Keeps the gases hot and the outside cooler. Common on boiler flues, generator exhausts and stacks.
Boiler fluesV
Variation
A change to the agreed scope of work, such as a longer route or extra steelwork, priced and agreed before it is done.
Guide: what we need to price your jobW
Wall plate
A load-bearing plate and bracket fixed to a wall that carries the weight of the flue above it. Lighter bands then keep the run in line.
Steelwork and supportsWind load
The force wind puts on a flue or stack above the roof. The supports and steelwork are designed to carry it.
Steelwork and supportsWant the longer version?
Our guides walk through pricing, surveys, old chimneys and handover paperwork.
Send drawings. Get a price.
Send what you have. A price normally comes back within 24 hours.