No, it wasn't as far as I can see.
There wouldn't be a chimney open to air in an "air tight" house.
One might thank that the balloon is to stop the chimney sucking air out of the house.
The opposite seems to be the case - when the fire is unlit, the chimney is a source of open entry for cold air from outside.
Anyone sitting opposite an open unlit fireplace with a chimney will confirm you can get a blast of cold air from it - its not venting air, its supplying it.
Cold damp air from outside is more dense than warm air inside - gas expands when warm, becoming less dense - the colder dense air displaces the air inside the house and moves down the chimney creating a draft.
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A similar principle, but using laminar flow that follows a surface, occurs at windows. The window, being colder than the room air, accepts heat from it,.
The air gets colder and becomes more dense and starts to descend along the pane of the glass in a laminar flow that makes your feet cold on the far side if the room - unless you have a radiator under the window to counteract this.
Laminar flows tend to remain coherent along a surface and not disperse.
http://www.commercialwindows.umn.edu/issues_hf4.php
So you can see that placing heat sources properly can help combat drafts from glazing.
Also a highly sealed house may give rise to problems with open fires unless there is supply air.
It pays to consider a building "in the round" and ask somebody competent for advice - it brings good results.
ONQ.
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All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.