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The Secret of Everyday Things by  Jean Henri Fabre


 

 

HEATING

[129]

"I
HAVE told you how man has possessed fire ever since the earliest times. The first fireplaces for preparing food and furnishing protection from cold consisted of armfuls of fagots burning between two stones, either in the open air or in the middle of the hut. This rude method of domestic heating still prevails among many savage tribes. On flagstones in the middle of the dwelling smolder a few firebrands, the smoke escaping as best it can through some chance cracks and crannies in the roof. Indeed, if you wish to view this primitive method of making a fire, you need not go to distant countries beyond the reach of the benefits of civilization. In certain mountain cantons of France the fireplace is still to be seen in the form of a large flat stone in the middle of the room, the walls and rustic furnishings of which have become coated by the action of smoke with a brilliant varnish as black as shoe-polish. The cracks in an imperfectly fitted roof furnish the only outlet for the products of combustion."

"The family must be nearly smothered to death," said Claire, "when the fire smokes in the middle of one of those chimneyless houses. Why don't they make a fire like ours?"

"Chimneys are a rather recent invention, and in [130] those remote mountain villages habit preserves old traditions indefinitely. Antiquity in its period of highest refinement knew absolutely nothing of our common chimney. A striking proof of this is given us by a celebrated city, Pompeii, which was buried in the year seventy-nine of our era under a bed of volcanic ashes thrown up by Mount Vesuvius. Its houses, after having been buried for eighteen centuries, are exhumed to-day by the miner's pick and come to light again as they were when overwhelmed by the volcano. Not one of them has a chimney. In the old Roman town people warmed themselves with burning charcoal placed in a large metal vessel on a bed of ashes. This portable fireplace was put in the middle of the room to be warmed, without the slightest reference to air currents or the escape of harmful gases engendered by the burning charcoal. And even in our own time, in Italy and Spain, similar open braziers are used."

"I should think," said Marie, "that there would be danger of accidents, or at least that the people would have headaches due to the burning charcoal."

"The mildness of the climate which does not call for air-tight houses, permits this vicious mode of heating in Spain and Italy; but braziers would be very dangerous in our homes, where windows and doors must be carefully closed during the winter. Unchanged air impregnated with the deleterious gases from combustion would soon lead to discomfort and even asphyxia.

"The first chimney-places for domestic use mentioned in history date from the fourteenth century. [131] Disproportionately large, very costly, burning whole trunks of trees for fuel, these chimney-places were at first constructed without any knowledge of how to economize heat. Immense fires were built, but with no resulting warmth proportioned to the fuel used. The subject of draft was not in the least understood, and it was not until the end of the last century that there was any clear perception of the truth that draft in a fireplace is caused by the difference in temperature between the air of the chimney-place and that outside.

"I will now call your attention to something you have witnessed a thousand times in winter when you sit around the red-hot stove. Light a piece of paper and wave it to and fro over the hot stove. You will see the burnt particles rise, whirling and ascending sometimes as high as the ceiling. Why do they rise thus? They do so because they are carried by the air which, being heated by contact with the stove, becomes lighter and forms a rising current. These light fragments of burnt paper show us the upward flow of the air just as pieces of floating wood indicate the current of water. Thus air that is heated becomes light and rises.

"There we have the explanation of the draft in a fireplace. When the fire is lighted in the fireplace, the air contained in the chimney is warmed, becomes lighter, and rises. The hotter the air and the higher the column of heated air, the more powerfully it rushes upward. At the same time that the hot air rises, cold air, which is heavier, flows toward the fireplace, accelerates combustion, becomes warm in [132] its turn, and joins the ascending column. In this way there is set up a continual current from the lower to the upper part of the chimney. To this incessant flow of air through the fireplace we give the name 'draft..'

"The prime requisites for a good draft can now easily be seen. First, the chimney must be entirely filled with hot air. If the channel is too large there is established at the top a descending current of cold air which mixes with the warm ascending current, slackens its course, and even makes it flow back into the room. Then the chimney smokes. A remedy for this is to make the chimney smaller at the top or else cap it with a sheet-iron pipe.

"Our chimneys are generally too large. Their faulty construction is necessitated by the method frequently employed for cleaning them. When a poor child of Savoy, all begrimed with soot, worms his way up the chimney by dint of much scraping of elbows and knees, in order to sweep the soot from the inner surface of the walls, the passage must be large enough to admit his body, even though the draft suffer in consequence. But if the sweeping is done in a more suitable manner with a small bundle of brushwood let down from above by a cord, there is no reason why the chimney should not be as narrow as may be necessary for a perfect draft.

"Often, too, the lower opening, the one from the chimney into the room, is too large. Then there enter the channel at the same time hot air from the central part where the fire is burning and cold air from the vacant lateral parts. This cold air [133] necessarily lessens the draft by mixing with the hot air and lowering its temperature; or it can even blow the smoke back into the room.

"As far as possible only hot air should enter the chimney, all cold air sucked in by the draft being made to traverse the mass of burning fuel before passing into the ascending flue. To this end, in properly constructed fireplaces, the inner opening is narrowed by making the enclosing walls of the fireplace run obliquely inward so that most of the air sucked in by the draft passes through the burning fuel and becomes warm.

"The slanting walls serve still another useful purpose: they send back into the room a part of the heat that would not otherwise be reflected. To increase their efficacy in this respect they are lined with glazed tiles, which by their polish reflect a great part of the heat.

"Finally, the top of the chimney should be equipped in such a manner as to keep out any gust of wind that might else go whistling down toward the fireplace and thus drive back the smoke. To this end the chimney is capped either with a chimney-pot, which offers obstruction to the inflow of outer air, or with a sheet-iron hood that turns with the wind and always points its opening to the leeward.

"On account of the great volume of air continually passing through its wide mouth, a fireplace gives to a room excellent ventilation, a condition indispensable to health in our close dwellings; but its utilization of heat is sadly defective, so far as warming is concerned, because the air heated by passing [134] through the fire is discharged into the outer atmosphere with no benefit to any one.

"It is just the opposite with stoves: they warm well, but they renew the air of a room very imperfectly. They warm well because the whole of their heated surface, that of the sheet-iron pipe as well as that of the stove itself, is in contact with the air of the room. Cast-iron stoves furnish quick and intense heat, but cool off as quickly if the fire dies down. Terra-cotta stoves, whether glazed or not, heat more slowly, but their action is more continuous, more gentle, more even; they retain their warmth a long time after the fire is out. The Swedes and the Russians, in their rigorous climate, use enormous brick stoves occupying an entire wall of the room. The smoke and other products of combustion, before escaping out of doors, circulate through this mass of masonry by numerous channels. A fire is lighted in the morning and left to burn for several hours; then, when the wood is all converted into glowing coals, every outlet is closed, and that suffices to maintain a gentle heat in the room until night, provided only the glacial outside air be not admitted. But this mild and equable temperature is secured only at the sacrifice of the purity of the atmosphere, which cannot be renewed in the tightly closed room.

"Our stoves have the same fault: they do not renew the atmosphere of a room well because they consume for the same amount of fuel much less air than a fireplace. In a stove, in fact, all the air that enters is used up in burning the fuel; in an open fire, on [135] the contrary, much air is drawn in that does not pass through the burning fuel, but escapes outside without having taken part in the act of combustion.

"Besides the disadvantage of furnishing poor ventilation, the cast-iron stove has still another defect. The intense heat that it throws out dries the air to such an extent as to make it unpleasant to breathe. The great thirst one feels near a very hot stove has no other cause. This dryness can be remedied by placing on the stove a vessel full of water, which in evaporating gives suitable humidity to the air. Finally, the various kinds of dust floating in the air burn on coming in contact with the red-hot stove, and give rise to disagreeable emanations. In short, if the stove is the best heating apparatus in respect to easy installation, economy of fuel, and utilization of heat, it is one of the most faulty from a hygienic standpoint, especially in a small room filled with many people."


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