What it is called, by market
One concept, four markets. Where a name means something else locally, the card says so rather than leaving you to find out on site.
United Kingdom
Same word, different thingflue
also chimney, flue liner, balanced flue, room-sealed flue
Flue and chimney are distinguished: the flue is the passage, the chimney the structure. A VENT in British usage almost always brings air in, which is the opposite direction.
Australia
Close, not identicalflue
also chimney, flue pipe, cowl
As the UK, with flue used for the metal pipe on a stove or heater far more often than chimney.
United Statesyours
Same word, different thingvent
also flue, chimney, vent connector, B-vent, direct vent
VENT is the standard word for a combustion outlet, which is the reverse of British usage. A direct vent appliance is the equivalent of a room-sealed balanced flue.
Canada
Same word, different thingvent
also flue, chimney, direct vent, chimney liner
As the United States, with vent used for both combustion outlets and plumbing vent stacks, which is a third meaning again.
The governing standard, by market
United Kingdom
Approved Document J / BS EN 1443
Combustion appliances and fuel storage systems, and the performance requirements and designation system for chimneys.
United States
NFPA 211 / NFPA 54
Chimneys, fireplaces, vents and solid fuel-burning appliances, and the national fuel gas code for venting.
Calculators for this
Each works in either measurement system, and the terminology on the page follows whichever market you have selected.
Frequently asked questions
- Is a flue the same as a chimney?
- The flue is the passage and the chimney is the structure around it, and the distinction matters most on an old house. A Victorian chimney stack commonly contains several separate flues, one per fireplace, rising side by side and separated only by a brick withe — so a single chimney can be serving three rooms with three independent passages, and a blockage or a leak in one says nothing about the others. It also explains a class of problem that baffles people: smoke from one room appearing in another, which is a withe that has broken down and let two flues communicate. The American word vent sidesteps the distinction entirely by naming the function, which is clearer in a modern installation and unhelpful when discussing an existing stack.
- What is a balanced flue, and why is it sealed from the room?
- It is a concentric arrangement that takes combustion air IN through the outer passage and sends products OUT through the inner one, so the appliance never draws air from the room it stands in — hence room-sealed. The American term is a direct vent, and it names the same thing. The reason it matters is that an open-flued appliance is in competition with the building for air: it needs a permanent air supply, it can be starved by an extractor fan, and it can spill combustion products back into the room when the house goes to negative pressure. A room-sealed appliance has neither problem, which is why it has become standard, and why a modern boiler needs no ventilation opening in the room while an older one did.
- Why does an old chimney need lining before a stove goes in?
- Because the flue it offers is the wrong size and the wrong condition for the appliance. An open fire needed a large flue moving a large volume of relatively cool gas; a modern stove produces a much smaller volume of hotter gas, and putting it into an oversized flue means the gases cool on the way up, lose buoyancy, and deposit tar rather than leaving. That is both a draught problem and a chimney fire risk. The second reason is integrity: the mortar joints and the withes in a stack of any age are rarely gas-tight, so products can leak into adjoining flues or into rooms the chimney passes through. A liner solves both by giving the appliance a correctly sized, continuous, sealed passage — which is why liner diameter is specified by the appliance and not by the chimney.