And the inventor saw the tired, worn look of the housewife, removed the
stove to the cellar and installed tin pipes from this central heater
to the various rooms, and then waited for applause and purchasers. It
seemed so simple, but it did not solve the problem entirely, for when
the wind blew from the north into the windows, it pressed out the warm
air from the exposed rooms, forced it down the pipes up through which
it was supposed to come, and then rushed it up the flues on the south
or warm side of the house, overheating this part and leaving the cold
rooms of the house unheated. The drum of the furnace over which the air
passed to receive its warmth from the burning coal would leak every
time fresh fuel was added, for the odor of coal-gas became very evident
throughout the house. Moreover, the heat was very dry and unpleasant,
so that water-jars had to be set about to moisten the air.
Then came the inventor again with a new device, a steam-boiler, pipes
to distribute the steam, and radiators to give off the heat in the
steam to the room. Here at last was a method of heating which would
supply warmth in the cold parts of the house, even under the windows,
through which the chilliest air penetrated. But the sizes of the
radiators were calculated to heat the house to 70 degrees when it was
zero outside, although the average winter day was much warmer than
this. In this way the occupants of the house were cooked with an excess
of heat during moderate weather, for there was no way to regulate the
amount of heat given off from the radiator; it either was filled with
steam, giving off its maximum quantity of heat, or else it was empty
and cold.
To meet this difficulty presented by the steam-heated radiator,
the hot-water system was developed. Instead of distributing heat
with the medium of steam which under low pressure was fixed at one
temperature, heat was circulated by hot water from the central boiler.
The temperature of this water could be regulated for mild weather by
lowering the fire. However, since the hottest water was cooler than
steam, it required larger radiators and more piping, so that the
initial cost of a hot-water plant was more than that of a steam system.
[Illustration: Simplified diagram of Vapor-vacuum system]
In order to overcome the disadvantages of the inflexible
steam-radiator, inventors finally developed the so-called
“vapor-vacuum” system of steam-heating. In this equipment the air was
driven from the entire length of pipes and from the radiators by the
pressure of the rising steam from the boiler, and forced through a
special ejector which closed when the steam came in contact with it,
preventing the return of air into the interior. Thus when the pipes and
radiators were filled with steam (there being no air left), no pressure
was set up to resist the circulation of the water vapor, and when the
hot steam condensed in a radiator to a thimbleful of water, more steam
was drawn in to take its place, for no air could enter the pipes. In
this way the quantity of steam delivered to the radiators could be
regulated by a special valve with a varying number of ports, and by
turning the valve to a certain position enough steam would be permitted
to enter the radiator to keep it half full, or by shifting the valve
to another point enough steam would enter to fill the radiator to
three-quarters of its capacity. In fact, the requisite amount of steam
could be admitted to the radiator to balance the speed of condensation
and retain whatever level of steam in it was desirable. Thus the steam
system became at once a flexible system of heating, and could meet the
changing requirements of the weather.
[Illustration: Hot water radiator heated by steam]
A further development of the hot-water system then came about. In this
device the radiators were made to contain water, but the heat was
circulated through the pipes by means of steam. This steam was poured
over the surface of the water in the radiator and transferred its heat
to it. According to the quantity of steam poured over the water, the
latter could be heated to various temperatures. Of course the water in
the radiator was the medium for distributing the heat outward from the
radiator itself.
Still another improvement was made upon the hot-water system by
introducing the principle of the closed expansion tank. In the ordinary
system the water is allowed to expand at the top through an expansion
tank, so that the actual pressure on the water of the system is
atmospheric. Under this pressure the temperature of the water cannot be
raised to more than 212 degrees Fahrenheit, for beyond this it boils
and changes to steam. However, in the closed-tank system a so-called
heat-generator is added on the line leading to the expansion tank,
which, by means of a column of mercury, is capable of adding 10 pounds
more pressure than the atmosphere to the water in the system, and thus
raising the boiling-point to about 240 degrees. This generator is so
designed, however, that, although it adds this greater pressure to
the water, yet the natural expansion of the water in the system is
permitted through it in case of emergency. By permitting the raising of
the temperature of the water, the size of radiators can be cut down 50
per cent, which, of course, reduces the quantity of water needed and
permits a quicker heating of the system when the fire is started. Thus
a saving of fuel is accomplished and the disadvantage of the ordinary
hot-water system is eliminated; namely, the long time required to get
hot water in the radiators after the fire is started in the morning
from its banked condition of the previous night.
[Illustration: Pipeless Furnace]
However, the genius of the inventor was not at rest on the problem of
warm-air heating, for he discovered that he could abolish the flues,
which he once thought were essential, and use but one register and one
flue. This is called the pipeless furnace. A register is employed
which has an outer and inner section. The outer section permits the
cold air from the house to pass down through it and over the drum of
the furnace. The inner section of the register permits this hot air to
escape upward and through the house by natural distribution. Thus the
hot air rises from, and the cool air settles back into, the furnace
without utilizing flues. The circulation of this system was found to
be superior to the older method as ordinarily installed, and very much
cheaper to install. In fact, it is the cheapest of all systems of
heating. It is especially adapted to the small, low-cost house.
[Illustration: Hot Water Heating—Boiler in Dining-Room]
To reduce the cost of hot-water heating and make it also available for
this class of small house, the manufacturers produced another type of
water heating-plant. In this device the water-heater was installed
in one of the rooms of the house, like a stove, but the exterior was
designed to serve as a hot-water radiator for the room in which it was
placed. From this heater pipes were taken off to distribute heat to
other radiators, located in adjoining rooms. The principle remains the
same as the former system; the only difference lies in the reduction of
cost by eliminating the boiler from the cellar and utilizing it to heat
the room in which it was placed.
Other attempts to improve the mechanics of heating have been more along
the line of perfecting the operation of valves or the utilization of
other fuels than coal. Gas-radiators have been tried, but they are so
expensive to operate in most parts of the country that they are not
always suited to the needs of the small house. Electric heaters, too,
are not within the pocketbook of the average person owning the small
house. Fuel oil-burners also have been devised to take the place of the
coal-grate. Wherever oil is cheap enough to permit their use they are
great labor-savers, since they eliminate all the shovelling of coal and
handling of ashes. These will be discussed later.
Briefly, then, the available systems for the heating of the small house
are:
_Hot-air.—a._ Furnace with flues.
_b._ Furnace without flues.
_Steam.—a._ Ordinary gravity system.
One-pipe.
Two-pipe.
_b._ Vapor-vacuum system.
_Hot-water.—a._ Ordinary open-tank system.
One-pipe.
Two-pipe.
_b._ Closed-tank system.
_c._ Special open-tank system with boiler used
as radiator.
_d._ Patent system using water in radiators but
steam for circulation.
_Methods Employed in Calculating the Required Size of Heater_
The basis of calculating the required size of any one of the systems
previously mentioned is to assume that a certain temperature of heat
is to be maintained when the weather is zero, and then by means of the
laws of heat transmission estimate the quantity of heat lost per hour
from the house. The amount of heat lost per hour is, of course, the
quantity which the heating system must supply. Knowing this, a system
is installed which is capable of supplying this heat loss.
In such devices as the warm-air furnace the required size can be
computed directly to meet the heat loss, but where radiators are used
the required sizes of these must first be determined to offset the
losses from the rooms in which they are installed, and then the size of
the heater must be estimated to supply sufficient heat to the radiators
and to make up for the losses of heat through the distributing-pipes.
The usual temperature to which the small house is heated when it is
zero outside is 70 degrees Fahrenheit. It is then assumed that a
certain quantity of heat is lost through the walls of the house by
radiation and convection and conduction, and another quantity lost by
the leakage of warm air out through the window-cracks. (The quantity of
heat is measured in British thermal units, called B. T. U.’s.)
To understand the manner by which heat is lost through the exterior
walls, it is necessary to know the meaning of radiation, convection,
and conduction.
By standing before an open fire the heat given off by radiation can be
observed by shutting it off with a piece of paper held between the face
and the fire. This is the transmission of the heat through the ether,
and is similar to the transmission of light, since this heat will pass
through glass, like light.
Convection of heat is illustrated by heating air in one place and
transferring that air to another place, where it will give up its heat
to surrounding bodies.
Conduction of heat is illustrated by heating the end of an iron rod and
noticing that the heat will eventually be transmitted along the length
of it to the other end.
The heat within a house escapes from the interior to the colder
atmosphere of the exterior through the walls, by radiation through the
glass windows and the substance of the walls, by the convection action
of the warm air of the interior giving up its heat to the interior
face of the wall and the cold air of the exterior extracting this heat
from the exterior face and carrying it off, and also by the action of
conduction of the materials of which the wall is composed.
The quantity of heat lost is measured by the number of B. T. U.’s lost
through one square foot of the wall each hour. As the window-glass
loses heat through it more quickly than the wall, it is necessary to
calculate this separately. The process, then, for estimating the heat
loss from a room is as follows:
1. Estimate the number of square feet of exposed wall surface
in the room, including windows.
2. Subtract from the above the area of the windows to find the
net wall area.
3. Multiply this net wall area by the number of B. T. U.’s
which the wall loses per square foot of surface for each hour.
These factors are given in the following table:
Zero outside and 70 degrees
inside—Number of B. T. U.’s
TYPE OF WALL lost for each square foot of
wall surface each hour
Brick wall, furred and plastered:
8" thick 21.0
12" thick 17.5
Frame wall, sheathed, clapboarded,
and plastered 21.7 (with building-paper use
20.3)
Hollow-tile wall and concrete and stone have factors about the same as
for the furred brick wall.
[Illustration: SIDE ELEVATION]
4. Add to this the number of B. T. U.’s lost per
hour through the windows. This is determined by
multiplying the area of the windows by the heat
loss in B. T. U.’s per hour for each square foot of
window, which is 78.8 for single windows, and where
storm-windows are added it is 31.5 B. T. U.’s.
5. This total sum is the number of B. T. U.’s lost
through walls and windows for each hour.
6. To this must be added the heat lost by leakage
through the window-cracks. This is secured by
measuring the length of window-cracks on the
side which has the greatest length of crack and
multiplying this by 168, or the number of B. T. U.’s
lost each hour for each linear foot of window-crack.
For very tight windows reduce above to 84.
7. The total of all the above gives the number of
B. T. U.’s lost each hour from the room when the
outside temperature is zero and the inside is 70
degrees Fahrenheit.
Knowing the quantity of heat lost per hour, a radiator must be
installed which will supply this amount per hour. As the average
steam-radiator supplies about 250 B. T. U.’s per hour from each square
foot of its surface, the number of square feet required for a radiator
to be installed in the room can be found by dividing 250 into the
number of B. T. U.’s which were found to be lost from the room each
hour.
A hot-water radiator gives off about 150 B. T. U.’s per hour for
each square foot of surface, so that the radiator is generally about
one-third larger than the steam-radiator.
Knowing the required number of feet of radiation for the radiator, the
proper size can be selected from the manufacturer’s catalogue.
By lumping the total number of square feet of radiation for all the
radiators throughout the house together and adding 35 per cent to this
to make up for loss through pipes and under-rating of boilers, the size
of the boiler can be selected from the catalogue to fit this need.
To estimate the size of a warm-air furnace, the total quantity of heat
lost from all the rooms of the house should be calculated in the same
way, and then 25 per cent added to allow for cold attics and exposure.
This quantity should then be multiplied by 2.4 and divided by 8,000
to find the number of pounds of coal which will be required to be
burned per hour. By dividing this amount by 5, the grate area of the
required furnace can be found, and the correct size selected from the
manufacturer’s catalogue.