requires four hundred or five hundred degrees of heat in the chimney.
I never saw an ordinary domestic fire of coals produce any noticeable
ventilating suction, without the use of a blower, urging the
combustion to fury, and I presume nobody else ever did.

But, while nobody ever saw an active suction of air produced by the
mere heat of a still or unexcited fire--unless the _quantity_ of heat
were on a very large scale--everybody has seen a roaring current
sucked through the narrowed throat of a chimney or a stove by a
blazing handful of shavings, paper, or straw. It is very remarkable,
when you come to think of it, that the burning of an insignificant
piece of paper, with less heat in it, perhaps, than a pea of
anthracite, will cause a rush of air that a bushel of anthracite
cannot in the least degree imitate. It is not only a curious but a
most important fact. In short, it is _the cardinal_ fact on which
ventilation practically turns. But what is the nature of it? There are
three factors in the phenomenon. In the first place, the mechanical
peculiarity of flame, or gas in the moment of combustion, as compared
with a gas like air merely heated, is _an almost explosive velocity of
ascent._ The physical peculiarity from which this results is the
intensity of its heat--commonly stated at 2,000 degrees, as to our
common illuminating gas--acting instantaneously throughout its mass,
just as in gunpowder. The gas goes up the flue in its own flash, like
the ignited charge in the barrel of a gun: the burning coals can only
_send_, and by a leisurely messenger, namely, the moderately heated
gases, and contiguous air, that rise only by the gravitation or
pressure of the surrounding atmosphere.

And yet it is not the small flame itself that roars in the chimney but
the rush of air induced by it. The semi-explosion of flame is but for