THE WARMING OF HOUSES.
=Physiological and Physical Considerations.=—The warmth of our bodies
is naturally kept up by the oxidation changes constantly going on
in the system. In Chapter XL., p. 265, are discussed the modes in
which heat is lost by the system, and the influence of clothing in
controlling the amount of this loss. Artificial warming of houses has a
similar action to clothing. It diminishes the demand on the system, and
so economises the amount of food required.
The degree to which this diminution of loss of heat by clothing and
artificial warming of houses may be carried varies with circumstances.
There can be no doubt that if food be abundant, exposure to external
cold, if not too extreme, is on the whole beneficial, for vigorous
people. But for old people and young children, means of artificial
warmth require to be more carefully provided. Severe cold is for them
often the harbinger of death.
The =Degree of Temperature= at which living-rooms should be kept will
vary with circumstances.
For _healthy adults_, any temperature between 50° and 60° Fahr., will
be moderately comfortable; for _delicate children and old people_ it
may be 65° with advantage.
For _sick rooms and hospitals_ the temperature of 60° is usually
adopted, but this is by no means always necessary. A temperature of
the room as low as 50°, except for such diseases as whooping cough and
bronchitis, suffices if the patient is well covered with warm personal
and bed coverings.
_Convalescents_ from any acute illness bear low temperatures badly.
=The Different Kinds of Heat.=—Heat may be communicated by radiation,
conduction, and convection. By =radiation of heat= is meant the process
by which heat passes from a fire or other source of heat, through a
vacuum, dry air or any other medium, without heating any of the media
through which it passes, but only the bodies against which it finally
impinges. The solid bodies (including ourselves) which are warmed by
radiant heat, by a process of conduction then warm the surrounding air.
This method is the nearest imitation of the natural warmth of the sun.
=Conduction of Heat= is the passage of heat from one particle to
another, whether it be of a gas or solid. It is an extremely slow
process when air is concerned, and may be practically ignored.
=Convection of Heat= is the process by which a gas or liquid actually
carries the heat in itself from one part to another. The heated
particles are relatively lighter, and ascend to the higher parts of a
room, while colder and heavier particles descend, and are subjected
to the same process. Heat can be carried by convection only by gases
and liquids. It is quite possible, therefore, for a person to be cold
in a room filled with warm air, if the walls, etc., are cold; and on
the other hand, to feel comparatively warm in a room filled with cold
air, if more heat is radiated from an open fire-place or the warm
walls to his body than he radiates to his surroundings. The feeling of
“draught” when sitting near a wall is sometimes caused by radiation of
heat from the body to the colder wall. The ideal arrangement, were it
practicable, would be to have cool air to breathe, but to be surrounded
by warm walls, floors, and furniture. A room warmed by an open fire
is more comfortable than a room warmed by hot air from a furnace,
assuming the temperature of the air is the same in both instances,
because the walls of the room are several degrees lower in temperature
in the latter than in the former. For warming walls as well as the air
high pressure steam pipes are more efficient than hot-water pipes. The
great advantages of radiant heat are that—(1) it heats the body without
appreciably heating the air; while at the same time (2) there is no
possibility of impure gases being added to the air.
It has, however, considerable disadvantages. (1) It is costly, though
its expense may be greatly diminished by a well-constructed fire-place.
(2) It only acts on bodies near it to any useful extent. Its effect
lessens as the square of the distance; thus, its warming effect at
five feet distance, is twenty-five times less than at a distance of
one foot. It is evident, therefore, that for long rooms, and for large
assembly-rooms, a single source of radiant heat is quite inadequate.
The immense loss of heat in our ordinary fire-places is slowly leading
to their modification; and although it is probable that radiant heat
will always be the favourite source of warmth in dwelling-houses, it
will be used for larger buildings chiefly as an adjunct to convection
of heat.
The different sources of heat are employed, either singly or combined,
in the following methods of warming our dwellings and other buildings:—
1. Warming by the open grate.
2. Warming by closed stoves.
3. Warming by hot-water pipes.
4. Warming by steam in pipes.
5. Warming by hot air.
6. Warming by electricity.
=Warming by the open Grate.=—In the open fire-place radiation is the
source of heat chiefly employed.
The =position of the fire-place= is important. It should not be on the
external wall of the house, as thus a large proportion of heat is lost;
but should be placed where the heat from the flue may be utilised in
keeping up the temperature of the house.
The =construction= of a fire-place is commonly faulty in several
respects. (1) The fire-place may be too far included in the wall, so
that the heat at once passes up the chimney. (2) It may be composed
chiefly of iron, which rapidly conducts away the heat, and does not
furnish a surface for radiation. (3) The bars and bottom of the grate
may be so arranged, that coal and cinders fall out in an incompletely
burnt condition.
It has been estimated that with an ordinary fire-place, seven-eighths
of the possible heat is lost, one-half being carried up the chimney
with the smoke, one-quarter carried off in the ascending current
of warm air, and one-eighth of the combustible matter remaining
unconsumed, forming the solid matter of the smoke.
The defects which have been indicated may be remedied by bringing the
fire-place rather further out into the room; by substituting fire-brick
for iron behind and at the sides of the fire, and by having a layer of
fire-brick at the bottom of the grate, or the grate lowered, so that as
in Teale’s stove, it lies on a bed of fire-brick at or below the floor
level.
The =shape of the grate= is important. The width of the back of the
grate should be about one-third that of the front, the sides sloping
out towards the front of the recess. The depth of the grate from before
backwards should be equal to the width of the back. The sides and back
of the fire-place must be made of fire-brick, thus ensuring the heat
being retained in the grate. And finally, the chimney throat must
be contracted so as to ensure more complete combustion. The =chief
objections to an open fire-place= are (1) the great waste of fuel
involved, even after the improvements indicated have been carried out.
(2) The unequal heating at different distances from the fire. (3) The
smoke and dust always produced to some extent, from accidental smoking
of the fire, or from the escape of ashes. (4) The trouble involved in
frequently replenishing the fire. (5) The cold draughts produced by the
currents of air towards the chimney. These travel chiefly along the
floor, when, as is commonly the case, the space between the bottom of
the door and the floor forms the chief place for the entry of fresh air.
Many patents have been brought out for the =introduction of the
fuel at the lowest part= of the fire. The uppermost part of the
fuel being first burnt, and the remainder attacked from above, the
smoke is consumed in passing through the red part of the fire. Thus
a comparatively smokeless fire is produced, and the amount of heat
evolved is greatly increased. So far none of these have been altogether
satisfactory. The production of _a comparatively smokeless fire_ is a
great boon. =Smoke= means so much unburnt fuel, and not only so but the
sooty particles float about in the atmosphere, rendering it impure, and
changing comparatively harmless mists into town fogs, which are loaded
with soot and the products of combustion, and do incalculable mischief
to health and property. The prevention of this =smoke nuisance=
demands more consideration than it has yet received. The Public
Health Acts constitute the emission of black smoke from the chimneys
of manufacturing premises a nuisance; and manufacturers can if they
use proper boilers, especially those in which mechanical stokers are
employed, almost completely obviate this nuisance. The great principle
is to prevent the escape of smoke before it is completely burnt. This
may be accomplished by careful stoking, by keeping the unburnt coal
at the front of the fire, and by ridges exposing the smoke to red-hot
fire-clay before it escapes. In domestic fires, gas is gradually
replacing coal for cooking, with a corresponding reduction of the
smoke-nuisance.
=The Utilization of the Heat Produced= in the fire-place to warm the
air on its way into the room, as in Galton’s and other similar stoves
has been already described (page 156).
A larger amount of heat can be obtained out of a given quantity of fuel
by cutting off some of the cold air, which rushes through the fire, and
carries the half-burnt gases and much of the heat up the chimney. This
is effected by having a solid fire-brick bottom to the grate, or by
closing up the front of the open chamber under the grate, by means of a
close-fitting shield or door. These “Economisers,” as Mr. Teale calls
them, appear to answer better than solid fire-brick bottoms, as they do
not prevent the ashes falling under the grate.
=The Fuel= burnt in an open fire-place may be either coal or coal-gas.
Occasionally coke is also employed. Coke and coal-gas have the
advantage over coal, that (1) no smoke is produced. Coal-gas presents
the additional advantages, that (2) it can be turned on at any moment,
without having to go through a tedious process of lighting the fire;
and that (3) the amount of heat can be exactly graduated by regulating
the supply of gas. A gas fire is however, as a rule, more expensive
than a coal fire.
=Open Gas-stoves= are made in various forms. In the common one, small
jets of gas are lit under the grate, which is filled with pieces of
asbestos. These become red hot, and radiant heat is emitted. To obtain
the greatest value from the heat generated by the combustion of gas,
a stove should be chosen in which the heat generated is brought into
contact with a large surface of the grate before the products of
combustion are allowed to escape to the flue.
Gas stoves which are advertised as not needing a flue, should be
avoided. A large amount of carbonic acid is discharged by them into the
room, and the sulphurous acid also produced by the combustion of gas is
not completely absorbed in the water of condensation which collects in
a tray under such stoves.
=Closed Stoves= form the most economical and efficient warmers for
rooms of moderate size, and coal, coke, coal-gas or paraffin may be
burnt in them.
_The advantages_ rightly claimed for coal stoves of this type are that
(1) the amount of fuel consumed is small; (2) by adjusting the damper,
combustion may be rendered as slow as desired, so that but little
heat is lost by the flue or chimney; and (3) heat radiates from all
parts of the stove into the room, and not simply from a small area of
fire-front.
_The chief objections_ to closed stoves are, that (1) they _dry_ the
air excessively, rendering it somewhat unpleasant. (2) They produce a
peculiar _close smell_, apparently caused by the charring of minute
particles of organic matter in the air, coming in contact with the
stove. If the air of the room is not heated above 75° Fahr., no
smell is produced, and the relative humidity is not lessened to any
appreciable extent (Parkes). But when the heat produced by the stove is
excessive, these results do follow. The unpleasantness may be modified
though not entirely removed, by placing shallow pans of water near the
stove.
(3) Portions of the _products of combustion_ may pass through cracks
or fissures in the stove, or even through the joints of the stove.
Independently of such accidental cracks, cast-iron stoves, when red
hot, appear to allow gases to pass through them with comparative ease.
Thus carbonic oxide and other gases may find their way into the room,
and it is probable that this rather than the dryness of the air, is the
cause of the unpleasant symptoms sometimes complained of in rooms where
closed stoves are in use. This escape of carbonic oxide does not occur
with earthenware stoves properly encased with fire-clay.
Many modifications of the older closed stoves are now in common use. In
the stove shown in Fig. 18, excessive heating of the air is prevented
by the presence of two air chambers, only the outer one, which brings
external air to be warmed, having its air emptied into the room.
[Illustration: FIG. 18.
SLOW COMBUSTION STOVE.]
Warming by open grates or closed stoves is specially applicable to the
rooms of private houses; warming by hot air or steam, or hot water,
is chiefly used for large buildings. It is quite possible that these
methods will be applied at some future time on a large scale to the
warming of private houses. In some large towns of the United States
this has been already done, blocks of a hundred or more houses being
warmed from the same centre, by the same system.
But apart from such a central system, hot air and hot water lend
themselves to the heating of houses on what may be called the _Whole
House System_ (page 156). We have mentioned in the last chapter some
methods of doing this, and shall now describe others.
=Hot-water Pipes= are probably the best means of carrying heat to
various parts of a large house, and hot water is more thoroughly under
control and less dangerous than either hot air or steam. There are _two
systems_ of heating by hot water.
In the first, which we may call the =low pressure system=, there is
a boiler from which water circulates through pipes to every part of
the building, and as it cools down returns again to the boiler. At
the highest points of the pipes, outlets are provided for air. In
this system the water is not heated above 200° Fahr., and there is
consequently no great pressure on the pipes.
In the =high pressure system= (Perkin’s patent), the pipes have an
internal diameter of about 1∕2 an inch, and have thick walls made of
two pieces of welded iron. There is no boiler, but one portion of the
tube passes through the fire and the water is heated to 300-350° Fahr.,
thus subjecting the pipes to great pressure. In dwelling-houses with
the low pressure system, for every 1,000 cubic feet of space to be
warmed to 50°, 12 feet of 4-inch pipe should be given; with Perkin’s
pipes, probably about two-thirds of this will suffice.
=Steam Distributed by Pipes= may be employed instead of hot water. This
method has been used in factories in which there is a surplus supply of
steam.
=Warming by Hot Air= is only applicable on a large scale, and should
only be used in association with a system of ventilation by propulsion
(page 153), in which the temperature, humidity, and freedom from dust
of the entering air are carefully regulated.
=Warming by Electricity= both for cooking food and for warming rooms
has a large future, but in most districts the supply of electricity is
not hitherto sufficiently cheap to be used for these purposes. By its
means the atmosphere will be prevented from becoming impure, labour
will be reduced, and life rendered more pleasant.
=Hot Water Supplies.=—Nearly every modern house is supplied with
a bathroom, and this may be supplied with hot water either from a
geyser or from the kitchen boiler. In a _geyser_ the water is made
to flow over a large heating surface furnished by burning coal-gas,
and with the best varieties a bath of 98° F. can be supplied in from
five to ten minutes. As the bathroom is usually small and unprovided
with an open fire-place, persons have occasionally been suffocated by
remaining in such a room while the gas continues burning. This is due
to the production and in-breathing of carbonic oxide. No geyser ought
to be allowed to be used which is unprovided with a flue passing into
the chimney flue or in its absence through an external wall of the
house. Short of fatal poisoning, violent headaches often occur when
a warm bath obtained by means of a geyser is taken, unless such a
flue is provided. In Ewart’s lightning geyser, additional protection
is furnished by the fact that a dual valve is so arranged, that
immediately the water is turned off or the supply fails from any cause,
the supply of gas is also cut off.
Hot water supplies from =kitchen boilers=, unless carefully arranged,
may be responsible for serious explosions during severe frosts.
Four plans are in common use. (1) _The worm-boiler system._ This
system is unsafe unless the supply of water to the boiler is attended
to; and as the hot water supply to the kitchen is drawn from the
boiler itself and not from the worm, the hot water supply for the rest
of the house may be deficient. Usually the small feed cistern for the
boiler in this system is too near the boiler to freeze.
(2) _The cylinder system_ is very effective. In this system a metallic
cylinder, capable of withstanding a pressure of 20 lbs. to the square
inch, is placed in the kitchen or bathroom between the cold and hot
supplies, its contained water being heated by circulation from the
boiler, hot water ascending and cold descending. On the top floor of a
house is a cistern from which cold water is supplied. Both the supply
pipe and escape pipe for hot water may become frozen during frost.
Then the supply of water is stopped, and the boiler and reservoir may
boil dry. This would not occur without some indication in unusually
vigorous boiling. Boilers sometimes explode, and cylinders sometimes
explode. This can be effectually prevented by (3) _A Double-cylinder
apparatus_ one within another. In this the water in the outer cylinder
supplied from the main cistern can only be heated to 212° F., and the
water in the boiler and inner cylinder supplied from a lower feed
cistern can only be heated to 214° F., on account of the small head of
water. Two escape pipes give free communication with the atmosphere.
(4) In the _tank system_, which being cheap, is usually adopted in
poor houses, the tank is placed high up in the system. The hot water
branch pipes are usually taken from the flow-pipe between the boiler
and tank. Hence when the supply fails, as during frost, the tank is
drained empty, the circulation of water ceases, and the system is
changed from a circulation system to a high-pressure one.
Safety valves cannot always be relied on to prevent explosions. If
they lead to the lighting of fires in frosty weather, when pipes are
frozen, they may cause explosions. Explosions from frost only occur
when both pipes are blocked. Incrustation of the boiler and pipes
increases the danger of explosions; hence the necessity for their
periodical cleaning.
[Illustration: Cylinder and Tank systems]