Sitting around the breakfast table we were unable to come up with a simple word for the exhaust out of modern chimneys. It's not really smoke because they aren't wood burning, but using exhaust seems too scientific.

Any ideas?

  • 1
    I would just refer to it as the 'central heating exhaust'. In the UK the vents through which these pass are not usually called chimneys, but flues. The gas that it most definitely must NOT be is carbon monoxide, and every home should have at least one carbon monoxide detector which bleeps if that gas is present. Remember that carbon monoxide is odorless and colourless, and can kill you before you realise you have breathed any. Many people die of CO poisoning from domestic appliances. – WS2 Feb 5 '14 at 16:03
  • I find it hard to think of exhaust as scientific, being a word I learned young in relation to cars long before I understood combustion well enough to know why cars would need one. – Jon Hanna Feb 5 '14 at 17:05

Exhaust would be an acceptable term. You could also call them emissions or gases. When using natural gas combustion, you get greenhouse gases. (CO2, CH4, and N2O emissions are all produced during natural gas combustion. Nearly all of the fuel carbon (99.9 percent) in natural gas is converted to CO2 during the combustion process. The amount of CH4, CO, and VOC produced is insignificant compared to CO2 levels)


"Flue gases" is a workable term for the exhaust from a furnace or fireplace, but it's not a single word.


I recently upgraded my gas central heating boiler, which under current UK regulations requires the outlet flue to be on a house wall (the old boiler vented through a chimney on the roof).

My neighbour was concerned about "smoke" drifting in through his bedroom windows. To allay his concerns I tell him that what he sees coming out of my new condensing boiler is really just...

vapour - particles of moisture or other substance suspended in air and visible as clouds, smoke, etc.


If you want an alternative to "smoke" or "exhaust", either "emission" or "vapor" would suffice. The particular choice should be driven by why you object to "smoke" and "exhaust."

  • If your implication of "smoke" is that it's cloudy, "exhaust" as in "the exhaust from the car" retains the same connotation of a gas that would be deadly in an enclosed room.
  • If you want to actually emphasize how much less deadly natural gas exhaust is, such as when comparing supplemental heating sources and you want to contrast with the "smoke" from a wood-burning furnace or the "exhaust" of a gasoline generator, "emission" is a good third choice with similar connotations.
  • Should you be in the business of selling or promoting natural gas burning appliances, "vapor" would be a choice that diminishes the implication of "deadly gas" while still not being entirely breathable "air."

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