is a still further improvement, and, except for a little complication
in construction, may be considered the best in action and results.
The advantages of underfed grates are, firstly, an abatement of the
smoke nuisance, full utilisation of the fuel, and more powerful
radiation from the top of fire, which is always incandescent. There
is commonly no provision made for the supply of air for combustion,
nor to replace that which is taken from the apartment by the draught
in the chimney--the cracks and fissures around doors and windows
sufficing for this purpose, is the too commonly general idea; but
for perfection in warming upon hygienic principles, there must be
a proper supply from external sources; but this will be more fully
treated under Ventilation; it will, however, be noticed that some of
the ventilating stoves make provision for this in themselves; this
particularly applies to Captain Galton’s principle.
_Close-Fire stoves._--The old form of close-fire warming and
ventilating stove is that known as the “Cockle.” It consists of a
closed circular fire-box with a dome top and a similar shaped outer
casing; between the fire-box and the casing is a space of a few
inches all round, known as the air-chamber, which by means of a pipe
is connected with the outer air. The action is similar to a flue; the
air within the air-chamber, being in contact with the heated surface
of the fire-box is warmed, and rises and flows out at the top through
an aperture provided at the top (as explained with the Wharncliffe
grate), or it is made with a nozzle at top to attach a pipe and carry
the warm air wherever required, so making it a hot-air furnace, in
which case it would be fixed in a basement or cellar as at the best
it is not ornamental, but this primitive form of stove has gone
somewhat into disuse.
[Illustration: 40. Thames Bank Iron Co.’s Stove.]
Where a continual genial warmth is required at little cost in an
apartment, the slow-combustion stove, such as that made by the Thames
Bank Iron Company, London, (Fig. 40), may be employed. The external
air is drawn in by a smoke-pipe channel and impelled through orifices
in the stove. The smoke can be made to pass out at any level in the
stove that may be found most convenient, but unless there is a high
chimney shaft 25 to 30 ft., an underground flue connection is not
recommended. The fuel, consisting of coke or cinders broken small,
is supplied at the top, the ashes or cinders being removed through
a sliding door at the base; a special soot-door is provided for
clearing the flue before lighting the fire.
This appears an appropriate moment to mention that additional results
can be obtained from close-fire stoves, by carrying the smoke flue
down, and just below the floor level, in a properly made channel, and
covered by a grating, as with hot-water pipes. It is known that a
good proportion of the heat must be carried away by the flue, so that
by this means nearly the whole of the heat evolved by combustion can
be utilised; but it is necessary to bear in mind that the Building
Act prescribes that no hot-air or smoke-pipe shall be nearer than 9
in. from any woodwork or inflammable material, and it is necessary
that the main flue be high, as a good draught is needed to withdraw
this nearly cold smoke or vapour, and in many instances where the
under-floor horizontal flue is of good length, a pilot stove or
rarifier is necessary at the foot of the main up-flue to keep up
the draught, but in most cases the rarifier is only needed at first
lighting. This arrangement is rarely applicable in dwelling-houses.
Improved forms of close-fire stoves are as multitudinous as
improvements in open-fire grates; they are made either wholly closed,
generally called “slow-combustion stoves,” and are arranged to burn
many hours without feeding; or, as convertible open and closed; the
latter have the advantage of the cheerful radiating fire when open.
“The Tortoise Slow-combustion Stove” (makers, Portway and Son,
Halstead, Essex) is finding a ready sale and considerable favour,
as maybe judged by the fact of its being obtainable at nearly any
ironmonger’s. This stove, as with the majority of slow-combustion
stoves, consists of an ornamental outer casing (cylindrical, square,
or hexagonal), the height being about 2½ times the diameter; this
casing is lined with fire-brick, and constitutes the fire-box; there
is an ash-box and door below, in which is fitted a ventilator or
damper to regulate the draught and speed of combustion. The fuel is
supplied through a door provided at the top, and the smoke outlet is
also placed near the top. In use, the fire-box is filled with coke
and cinders, and the draught is regulated by the ventilator; it will
then burn, and heat an apartment for many hours without attention.
It is a very useful form of stove for greenhouses (in which case it
would be fitted with a vaporising pan), halls, offices, &c., but
hardly suited for living-rooms; the fire-brick lining tempers the
heat, but if in use where children or dresses would come in contact,
a guard must be provided. Slow-combustion stoves are made in a
variety of forms, and the effect is very pleasing when externally
fitted with tiled panels, &c.
For slow-combustion stoves that are required to burn for a longer
than usual period without attention a chamber or hopper is fitted on
top to take a further charge of fuel; it is taper-sided and open at
the bottom, very much like an inverted pail, but about 2½ ft. high.
It will be readily understood that as the coke is consumed, the upper
supply gradually sinks down until the whole is consumed; this would
utterly fail with a fuel that cakes, such as soft or bituminous coal.
[Illustration: 41. Musgrave’s Stove.]
“Musgrave’s Patent Warming and Ventilating Stove,” Fig. 41 (Musgrave
& Co., Limited, 97 New Bond Street, London), is made upon the
slow-combustion principle, to burn from 8 to 24 hours, but is much
more highly finished than the last named, and is constructed in so
many patterns and sizes as to be suitable for almost every purpose,
from small dwellings to the largest buildings. The stove consists
of an outer casing, within which is contained the fire-box and an
air-chamber. The latter is provided with gills to increase the
heating surface (see Gill stoves). The smoke and heat when leaving
the top of the fire-box is carried down a flue-way to the bottom of
the stove, and then up to the top again into the smoke-pipe; this
flue-way is within the air-chamber, and so utilises the major portion
of the heat passed into the flue; the fuel to be used is coke, which
is the most suitable fuel for all slow-combustion stoves.
For conservatories or where the air requires moistening these
stoves are very neatly and effectually fitted with vaporising pans;
and these stoves are also made to act as hot-air furnaces, and in
combination with hot-water-pipe heating apparatus.
Roberts’ patent terra-cotta stoves operate also by slow combustion
and are self-acting, but possess the additional advantage of
purifying and radiating the heat by the terra-cotta, which is
contained between 2 concentric cylinders of sheet iron united at
the base and top, the outer cylinder being perforated to allow of
direct radiation of heat from the terra-cotta. The stove consists
of 4 separate parts, namely, the stove body, its top or cover, the
fire-box, which can be lifted in and out, and the stand, with draw
and damper. The fire is lighted at the top and burns downwards, the
air sustaining it being drawn upwards through the bottom of the
fire-box and thence through the fuel. The stove can be placed in any
position on an iron or stone base and connected with the nearest
chimney flue by an iron pipe provided with soot-door elbows, care
being taken to form a complete connection by abandoning any other
open fire-grate in the room and screening it off by an iron or zinc
plate. They emit no effluvium, as the terra-cotta gradually and
completely absorbs all the caloric in its permeation through the
shell before it is communicated to the outer air, which is thus
warmed and diffused in a healthy condition over the room. The top
of the stove is movable, so that the fire-box can be removed to be
cleaned and recharged without moving the stove body, and a sand
groove is inserted at the top where the cover rests, which is filled
with fine dry sand to prevent any escape of smoke.
Close-fire stoves, consisting of a strong iron fire-box, on to the
outside of which is cast a series of vertical, parallel plates or
ribs, are known as “Gill” stoves, as the plates or ribs referred to
somewhat resemble the gills of a fish. These stoves are provided
with a door for replenishing the fire, with ash-pan and ventilator
below, and the iron base upon which the stove stands is made hollow,
and has a series of holes or perforations opening between the gills,
and provision is made for connecting the base with the outer air
whenever convenient. It must now be explained that the object of
the gills is to extend the heat-giving surface of the stove. It is
known that iron is a very rapid conductor of heat, and consequently
when the iron of the fire-box becomes heated, the heat is as quickly
transferred to and felt at the extremities of the gills. It will
be readily understood that only a certain amount of heat is given
off by the fire, and the greater amount of metal it is transferred
to, the lower must be its temperature; this is the chief and real
advantage, as instead of a small volume of air being heated to a
very high temperature, off a plane surface that would possibly get
red hot, there is a larger volume of air at a lower temperature, and
this has the further decided advantage that the air does not become
unpleasantly dry, and the particles of dust, &c., in the air do not
get scorched and burnt, and cause the unpleasantness commonly known
as “burning the air.”
A further advantage possessed by these stoves is that they are not so
much a source of danger, as the size of the gills is so proportioned
to the size of the fire-box, that in ordinary use they cannot become
excessively hot, and this is especially desirable where children or
ladies’ dresses, &c., might come in contact.
These stoves can be obtained at any ironmonger’s or stove maker’s.
A good form is that made by the London Warming and Ventilating Co.,
14 Great Winchester Street, London, and is called the “Gurney”
stove (Fig. 42). This is circular or cylindrical in form, with a
dome top, and the gills, which are perpendicular, extend around the
stove. A novel feature with this stove is that it is provided with a
water-pan or trough carried round the base of the gills; when this
pan is charged, the lower ends of the gills are immersed, and the
heat that is conducted there causes the water to slowly evaporate.
The advantage of a vaporising pan is this: before being warmed by
an ordinary stove, fresh air holds a certain and proper amount of
moisture, but as it becomes heated by such a stove the temperature is
raised without proportionately increasing the moisture, and this is
apt to make it unpleasantly dry, particularly to those suffering from
asthma or any bronchial affection. The reverse is the case when the
air becomes heated naturally (except when the wind is in the east);
the proper proportion of moisture increases as the temperature rises;
for instance, the atmosphere at 80° F. would contain about four times
as much moisture as when at 32° F. The principle of the Gurney stove
is such that the _natural_ degree of moisture is always maintained in
the heated air. The greater proportion of modern close fire-stoves
and furnaces have gills applied in some form or other.
It might be mentioned that 13 Gurney stoves have effectually coped
with the problem “How to heat St. Paul’s.”
[Illustration: 42. Gurney Stove. 43. Convoluted Stove.]
Another good form is “Constantine’s Convoluted Stove” (J. Constantine
and Son, 23 Oxford Street, Manchester), Fig. 43. Instead of solid
gills, there are a series of perpendicular convolutions which double
the heating surface, and the makers’ claim to greater efficiency is
no doubt correct. This stove, however, should be classed with hot-air
furnaces, as it is not made in small sizes for direct heating; but
for warming large buildings, churches, &c., for heating laundry
drying-rooms, Turkish baths, &c., it is to be highly recommended.
The German principle, which might advantageously be adopted to a
greater extent in England, is to build a fire-brick structure with
the furnace at the base and the flue winding from side to side 3 or
4 times, and terminating at the top into an ordinary brick chimney;
this structure projects into the apartment and is covered with
porcelain ware, and the appearance often exhibits great taste and
skill, as it will be understood that the structure is not rigidly
square, but is often very beautiful from an architectural point of
view. The good effect experienced is that after 3 or 4 hours’ firing,
the mass of brickwork becomes thoroughly heated and the fire is
permitted to go out; communication with the chimney is stopped by
means of a damper, and every confidence can then be placed in the
stove giving out abundance of warmth for the remainder of the day, as
the brickwork takes hours to become moderately cool, and the whole
of the heat it contains must be diffused into the apartment. It
will be noticed that a minimum of heat is lost by this arrangement,
and the result is very satisfactory from an economical standing; but
it has not the cheerful appearance of our open fires, and efficient
ventilation is required. This plan can, however, be satisfactorily
adopted for halls or cold situations; in the former it has the
further advantage in most instances of warming the stairways and
landings in the upper part of the house by the ascension of the
heated air. Fire-brick stoves are made by Doulton & Co., Lambeth,
London, and are finished in their majolica and Doulton ware; it
is needless to add, these wares give the stoves a very handsome
appearance.
_Hot-air Furnace._--The close stove is really a hot-air furnace,
but it is restricted to heating the air in the room. Other hot-air
furnaces are designed to obtain a supply of fresh air and heat it
before passing it into the room. The heated air from a fireplace is
available to the apartment for only about 12 per cent. of the total
amount of heat produced; all the rest passes up the chimney. The
close stove, on the contrary, utilises 85-90 per cent. of the heat
produced, and loses through the smoke-pipe only about as much as the
open fireplace saves--10-15 per cent. And herein lies the striking
difference between the relative healthiness of the atmosphere heated
by a close stove and an open fireplace. The amount of air which
hourly passes through a close stove, heated with a brisk fire, is, on
an average, equal to only about 1/10 the capacity of the room warmed,
and consequently such stove requires, if unaided, 10 hours to effect
a change of the atmosphere in every such apartment. Thus stagnant and
heated, the air becomes filled with the impurities of respiration and
cutaneous transpiration.
Moisture, too, is an important consideration. The atmosphere, whether
within doors or without, can only contain a certain proportion of
moisture to each cub. ft., and no more, according to temperature.
At 80° F. it is capable of containing 5 times as much as at 32°
F. Hence, an atmosphere at 32° F., with its requisite supply of
moisture, introduced into a confined space and heated up to 80°
F., has its capacity for moisture so increased as to dry and
wither everything with which it comes in contact; furniture cracks
and warps, seams open in the moulding, wainscoting, and doors;
plants die; ophthalmia, catarrh, and bronchitis are common family
complaints, and consumption is not infrequent. But this condition
of house air is not peculiar to stove-heat. It is equally true of
any overheated and confined atmosphere. The chief difference is,
that warming the air by means of a close stove is more quickly
accomplished and more easily kept up than by any other means.
Sometimes, by the scorching of dust afloat in the atmosphere, an
unpleasant odour is evolved which is erroneously supposed to be a
special indication of impurity, caused by the burning air. It is an
indication of excessive heat of the stove. But the air cannot be said
to burn in any true sense of the word, for it continues to possess
its due proportion of elementary constituents. Such is the close
stove and its dangers, under the most unfavourable circumstances.
The essentials for healthy stove-heat are brick-lined fire-chamber,
ventilating or exhaust-flue for foul air, means for supplying
moisture, and provision for fresh-air supply. A brick lining is
requisite for the double purpose of preventing overheating, and for
retaining heat in the stove. For the supply of moisture the means
are simple and easy of control, but often inadequate. An efficient
foul-air shaft may be fitted to the commonest of close stoves by
simply enclosing the smoke-pipe in a jacket--that is, in a pipe
of 2 or 3 in. greater diameter. This should be braced round the
smoke-pipe, and left open at the end next the stove. At its entry
into the chimney, or in its passage through the roof of a car, as
the case may be, a perforated collar should separate it from the
smoke-pipe. For stoves with a short horizontal smoke-pipe, passing
through a fire-board, the latter should always be raised about 3 in.
from the floor. A smoke-pipe thus jacketed, or fire-board so raised
at the bottom, affords ample provision for the escape of foul air.
Hot-air furnaces are simply enclosed stoves placed outside the
apartments to be warmed, and usually in cellars or basements of the
buildings in which they are used. The manner of warming is virtually
the same as by indirect steam heat--by the passage of air over the
surface of the heated furnace or steam-heated pipes, as the case
may be, through flues or pipes provided with registers. The most
essential condition of satisfactory warming by a hot-air furnace is
a good chimney-draught, which should always be stronger than that of
the hot-air pipes through which the warmed air is conveyed into the
rooms, and this can be measured by the force with which it passes
through the registers. A chimney-draught thus regulated effectively
removes all emanations; for, if the chimney-draught exceeds that of
the hot-air pipes, all the gaseous emanations from the inside of the
furnace, and if it have crevices, or is of cast iron and overheated,
all around it on the outside will be drawn into the chimney. Closely
connected with this requirement for the chimney-draught is the
regulating apparatus for governing the combustion of fuel--the
draught of the furnace. This should all be below the grate; there
should be no dampers in the smoke-pipe or chimney, and all joints
below and about the grate should be air-tight. The fire-pot should be
lined with brick and entirely within the surface, but separate from
it, so that the fresh air to be warmed cannot come in contact with
the fuel-chamber.
An excellent plan for economising a good portion of the waste heat
from a kitchen range is to have (previous to the range being fixed,
or after, in some instances) a sheet-iron box or chamber made to fit
at the back of the oven flues or wherever the most intense heat is
felt. This box, which we may call an air-chamber, should be connected
with the outer air, and a pipe for the warm air carried from the top
of the box to the part where warmth is required; the heat from the
range warms the air in the box and it ascends in exactly the same
manner and upon the same principle as a hot-air furnace, but great
care must be exercised to see that this box and all connections are
made air-tight, or this plan will prove an unusually speedy means of
indicating what is being cooked for dinner.
The Americans adopt what is called the “drum” principle of heating
by means of a furnace; they not only encase the stove with an
air-chamber, but the smoke-pipe is surrounded with a larger pipe
encasing it all the way up; the space between the smoke-pipe and the
outer pipe is thus an air-chamber and has free connection with the
furnace air-chamber, but of course is closed at top; from the chamber
surrounding the smoke-pipe, branch pipes are taken to the apartments,
terminating in perforated cylindrical “drums,” from which the heated
air is emitted.
It should go without saying that the air which passes from furnaces
into living-rooms should always be taken from out of doors, and be
conveyed in perfectly clean air-tight shafts to and around the base
of the furnace. Preferably, the inlet of the shaft, or cold-air box,
should be carried down and curved at a level (of its upper surface)
with the bottom, and full width of the furnace. Thus applied, the
air is equally distributed for warming and ascent through the
hot-air pipes to the apartments to be warmed. On the outside the
cold-air shaft should be turned up several feet from the surface of
the ground, and its mouth protected from dust by an air-strainer. A
simple but effectual way is to cover the mouth with wire cloth, and
over this to lay a piece of loose cotton wadding. This may be kept
in place with a weight made of a few crossings of heavy wire, and it
should be changed every few months. And here, too, outside the house,
should be placed the diaphragm for regulating the amount of cold-air
supply, and not, as commonly, in the cellar.
As the best means of regulating the temperature and purity of
the atmosphere from hot-air furnaces, it is necessary to provide
sufficiently large channels for both the inlet of fresh air and its
distribution through the hot-air pipes. The area of the smallest
part of the inlet (or inlets, for it is sometimes better to have
more than one) should be about ⅙ sq. ft. for every lb. of coal
estimated to be burnt hourly in cold weather; and to prevent, in a
measure, the inconvenience of one hot-air pipe drawing from another,
the collective area of the hot-air pipes should not be more than ⅙
greater than the area of the cold-air inlet. These proportions will
admit the hot air at a temperature of about 120° F. when at zero
outside, and the velocity through the register will not exceed 5 ft.
per second.
A large heating surface of the furnace is a well-recognised condition
of both economy and efficiency. As a rule, there should be 10 sq.
ft. of heating surface to every lb. of coal consumed per hour, when
in active combustion; and the grate area should be about 1/50 of
that of the heating surface. For the deficiency of heat, or the
failure of some of the hot-air pipes of hot-air furnaces in certain
winds and weathers in large houses or specially exposed rooms,
the best addendum is an open fire-grate. With this provision in
northerly rooms, to be used occasionally, hot-air furnaces may be
made to produce all the advantages of steam heat in even the largest
dwelling-houses.
[Illustration: 44. Boyle’s Warm-air Stove.]
Boyle’s system of warming fresh air is suitable where hot air,
water, or steam pipes are not available. The arrangement (Fig. 44)
consists of a copper or iron pipe _a_ about 1½ in. diam. placed in
an inlet tube _b_, preferably of the form of a bracket. This pipe
is not vertical, as in the so-called Tobin’s shafts, but of zigzag
shape, crossing and recrossing the tube from top to bottom, and so
causing the incoming air to repeatedly impinge in its passage through
the tube. At the bottom of the tube an air-tight chamber, so far as
the interior of the tube is concerned, is fixed, in which a Bunsen
gas-burner _c_ is placed, the flame of which plays up into one of
the lower ends of the pipe, the upper portion being about 5 ft. 9
in. from the floor. The other lower end of the pipe either dips into
a condensation box _d_ in the bottom of the tube or is continued
into an existing flue or extraction shaft. If the pipe terminates
in a box, the vapour is condensed there and carried off through the
outside wall by means of a small pipe. At the bottom of the box is
placed some loose charcoal, which needs renewing at intervals. This
charcoal absorbs any products of combustion which have a tendency to
rise. The heat thus passes through the entire length of the pipe, and
warms the air as it travels through the tube to the room or hall as
required.