Basically, it is a presentation on furnace and dryer. Here, different topics are presented, for example: what is furnace, different types of furnace, furnace and kilns, their difference, classification of furnace depending on types, furnace construction mechanism, factors and selection process of raw material. Besides, steel meal furnace, ceramic furnace etc are presented.

1. Course Name: Energy Engineering and Furnaces
Class Conducted By:
Md. Mintu Ali
Assistant Professor, Dept. of GCE, RUET
Rajshahi-6204
Email: min2.gce11ruet@gmail.com
Course No: GCE4241
1

2. GCE4241 (Energy Engineering and Furnaces)
Study of Different Furnaces/Kilns: Types of industrial furnaces and kilns.
Components of total furnace systems, Evolution of kilns in ceramic industries,
Furnaces/kiln construction materials.
Heat/fuel economy: Sources of heat loss in furnace, Thermal efficiency in operation of
furnace, Waste heat recovery - Recuperators & Regenerators.
Dynamics of Gas in a Furnace: Importance of draught, Classification of draughts.
Deduction of the equations for natural draught & chimney height.
Burners and Fire boxes: Grate firing systems, Mechanical stokers, Selection of
burners, Burner components and classification of burners.
Temperature Measurement: Principle, Thermometric properties, Heat work
measurement,
Resistance thermometer, Thermocouple, Radiation & Optical pyrometers. Temperature
controllers.
2

3. Reference Books:
1. Industrial_Ceramics, Felix_and_Sonja_S._Singer
2. Industrial Furnaces, Sixth Edition. W. Trinks
3. Thermal Engineering by RK Rajput
3

4. Contents
 Industrial Furnace/Kiln
 Classification of Industrial Furnace/Kiln
4

5. INDUSTRIAL PROCESS HEATING FURNACES
 Industrial process heating furnaces are insulated enclosures designed to deliver heat
to loads for many forms of heat processing.
 Melting ferrous metals and glasses requires very high temperatures,* and may
involve erosive and corrosive conditions.
Shaping operations use high temperatures* to soften many materials for processes
such as forging, swedging, rolling, pressing, bending, and extruding.
 Treating may use midrange temperatures* to physically change crystalline structures
or chemically (metallurgically) alter surface compounds, including hardening or
relieving strains in metals, or modifying their ductility. These include aging,
annealing, austenitizing, carburizing, hardening, malleablizing, martinizing,
nitriding, sintering, spheroidizing, stress-relieving, and tempering.
5

6.  Industrial processes that use low temperatures* include drying, polymerizing,
and other chemical changes.
 Industrial furnaces that do not “show color,” that is, in which the temperature
is below 1200 F (650 C), are commonly called “ovens” in North America.
 However, the dividing line between ovens and furnaces is not sharp, for
example, coke ovens operate at temperatures above 2200 F (1478 C).
 In Europe, many “furnaces” are termed “ovens.” In the ceramic industry,
furnaces are called “kilns.”
 In the petrochem and CPI (chemical process industries), furnaces may be
termed “heaters,” “kilns,” “afterburners,” “incinerators,” or “destructors.”
 The “furnace” of a boiler is its ‘firebox’ or ‘combustion chamber,’ or a fire-
tube boiler’s ‘Morrison tube.’
6

7.  Industrial heating operations encompass a wide range of temperatures, which depend
partly on the material being heated and partly on the purpose of the heating process and
subsequent operations.
CLASSIFICATIONS OF FURNACES
Furnace Classification by Heat Source
 Heat is generated in furnaces to raise their temperature to a level somewhat above the
temperature required for the process, either by (1) combustion of fuel or by (2) conversion of
electric energy to heat.
 Fuel-fired (combustion type) furnaces are most widely used, but electrically heated furnaces are
used where they offer advantages that cannot always be measured in terms of fuel cost.
 In fuel-fired furnaces, the nature of the fuel may make a difference in the furnace design, but
that is not much of a problem with modern industrial furnaces and combustion equipment.
 Additional bases for classification may relate to the place where combustion begins and the
means for directing the products of combustion.
7

8. Furnace Classification by Batch or Continuous, and by Method of Handling Material
into, Through, and out of the Furnace
 Batch-type furnaces and kilns, termed “in-and-out furnaces” or “periodic kilns” (figs.
1.1 and 1.2), have one temperature set-point, but via three zones of control—to maintain
uniform temperature throughout, because of a need for more heat at a door or the ends.
 They may be loaded manually or by a manipulator or a robot. Loads are placed in the
furnace; the furnace and it loads are brought up to temperature together, and depending on
the process, the furnace may or may not be cooled before it is opened and the load
removed—generally through a single charging and discharging door.
 Batch furnace configurations include box, slot, car-hearth, shuttle, bell, elevator, and bath
(including immersion). For long solid loads, crosswise piers and top-left/bottom-right
burner locations circulate for better uniformity.
 Bell and elevator kilns are often cylindrical. Furnaces for pot, kettle, and dip-tank
containers may be fired tangentially with type H flames instead of type E shown.
8

9. 9

10. Fig. 1.1. Seven (of many kinds of) batch-type furnaces.
10

11.  Car-hearth (car type, car bottom, lorry hearth) furnaces, sketched in figure 1.1,
have a movable hearth with steel wheels on rails.
 The load is placed on the car-hearth, moved into the furnace on the car-hearth,
heated on the car-hearth, and removed from the furnace on the car-hearth; then the
car is unloaded.
 Cooling is done on the carhearth either in the furnace or outside before unloading.
 This type of furnace is used mainly for heating heavy or bulky loads, or short runs
of assorted sizes and shapes.
 The furnace door may be affixed to the car. However, a guillotine door (perhaps
angled slightly from vertical to let gravity help seal leaks all around the door
jamb) usually keeps tighter furnace seals at both door-end and back end.
 Sealing the sides of a car hearth or of disc or donut hearths of rotary hearth
furnaces is usually accomplished with sand-seals or water-trough seals.
11

12.  Continuous furnaces move the charged material, stock, or load while it is being heated.
Material passes over a stationary hearth, or the hearth itself moves.
 If the hearth is stationary, the material is pushed or pulled over skids or rolls, or is
moved through the furnace by woven wire belts or mechanical pushers.
 Except for delays, a continuous furnace operates at a constant heat input rate, burners
being rarely shut off.
 A constantly moving (or frequently moving) conveyor or hearth eliminates the need to
cool and reheat the furnace (as is the case with a batch furnace), thus saving energy.
 Horizontal straight-line continuous furnaces are more common than rotary hearth
furnaces, rotary drum furnaces, vertical shaft furnaces, or fluidized bed furnaces.
12

13.  Figures 1.3 and 1.4 illustrate some variations of steel reheat furnaces. Side discharge
(fig. 1.4) using a peel bar (see glossary) pushing mechanism permits a smaller opening
than the end (gravity dropout) discharge of figure 1.3.
 The small opening of the side discharge reduces heat loss and minimizes uneven
cooling of the next load piece to be discharged.
 Other forms of straight-line continuous furnaces are woven alloy wire belt conveyor
furnaces used for heat treating metals or glass “lehrs” (fig. 1.5), plus alloy or ceramic
roller hearth furnaces (fig. 1.6) and tunnel furnaces/tunnel kilns (fig. 1.7).
 Alternatives to straight-line horizontal continuous furnaces are rotary hearth (disc or
donut) furnaces (fig. 1.8), inclined rotary drum furnaces (fig. 1.10), tower furnaces,
shaft furnaces (fig. 1.11), and fluidized bed furnaces (fig. 1.12), and liquid heaters and
boilers
13

14. Fig. 1.3. Five-zone steel reheat furnace. Many short zones are better for recovery from effects of mill delays.
Using end-fired burners upstream (gas-flow-wise), as shown here, might disrupt flame coverage of side or
roof burners. End firing, or longitudinal firing, is most common in one-zone (smaller) furnaces, but can be
accomplished wit
14

15. Fig. 1.4. Eight-zone steel reheat furnace. An unfired preheat zone was once used to lower flue gas exit
temperature (using less fuel). Later, preheat zone roof burners were added to get more capacity, but
fuel rate went up. Regenerative burners now have the same low flue temperatures as the original
unfired preheat zone, reducing fuel and increasing capacity.
15

16. Fig. 1.5. Continuous belt-conveyor type heat treat furnace (1800 F, 982 C maximum).
Except for very short lengths with very lightweight loads, a belt needs underside supports
that are nonabrasive and heat resistant—in this case, thirteen rows, five wide of vertical 4
in. (100 mm) Series 304 stainless-steel capped pipes, between the burners of zones 2 and
4. An unfired cooling one is to the right of zone 3.
16

17. Fig. 1.6. Roller hearth furnace, top- and bottom-fired, multizone. Roller hearth furnaces fit in
well with assembly lines, but a Y in the roller line at exit and entrance is advised for flexibility,
and to accommodate “parking” the loads outside the furnace in case of a production line
delay. For lower temperature heat treating processes, and with indirect (radiant tube) heating,
“plug fans” through the furnace ceiling can provide added circulation for faster, more even
heat transfer. Courtesy of Hal Roach Construction, Inc.
17

18. Fig. 1.7. Tunnel kiln. Top row, end- and side-
sectional views showing side burners firing
into fire lanes between cars; center, flow
diagram; bottom, temperature vs. time
(distance). Ceramic tunnel kilns are used to
“fire” large-volume products from bricks and
tiles to sanitary ware, pottery, fine
dinnerware, and tiny electronic chips.
18

19. Fig. 1.8. Rotary hearth furnace, donut type,
sectioned plan view. (Disk type has no hole in
the middle.) Short-flame burners fire from its
outer periphery. Burners also are sometimes
fired from the inner wall outward. Long-flame
burners are sometimes fired through a sawtooth
roof, but not through the sidewalls because
they tend to overheat the opposite wall and
ends of load pieces. R, regenerative burner; E,
enhanced heating high-velocity burner.
19

20.  Rotary hearth or rotating table furnaces (fig. 1.8) are very useful for many purposes.
Loads are placed on the merry-go-round-like hearth, and later removed after they have
completed almost a whole revolution.
 The rotary hearth, disc or donut (with a hole in the middle), travels on a circular track.
The rotary hearth or rotating table furnace is especially useful for cylindrical loads,
which cannot be pushed through a furnace, and for shorter pieces that can be stood on
end or laid end to end. The central column of the donut type helps to separate the
control zones.
 Multihearth furnaces (fig. 1.9) are a variation of the rotary hearth furnace with many
levels of round stationary hearths with rotating rabble arms that gradually plow
granular or small lump materials radially across the hearths, causing them to eventually
drop through ports to the next level.
20

21.  Inclined rotary drum furnaces, kilns, incinerators, and dryers often use long type F or type
G flames (fig. 6.2). If drying is involved, substantially more excess air than normal may be
justified to provide greater moisture pickup ability. (See fig. 1.10.)
 Tower furnaces conserve floor space by running long strip or strand materials vertically on
tall furnaces for drying, coating, curing, or heat treating (especially annealing). In some
cases, the load may be protected by a special atmosphere, and heated with radiant tubes or
electrical means.
 Shaft furnaces are usually refractory-lined vertical cylinders, in which gravity conveys
solids and liquids to the bottom and by-product gases to the top. Examples are cupolas,
blast furnaces, and lime kilns.
21

22. Fig. 1.9. Herreshoff multilevel furnace
for roasting ores, calcining kaolin,
regenerating carbon, and incinerating
sewage sludge.
22

23. Fig. 1.10. Rotary drum dryer/kiln/furnace for drying, calcining, refining,
incinerating granular materials such as ores, minerals, cements,
aggregates, and wastes. Gravity moves material co-current with gases.
23

24. Fluidized bed furnaces utilize intense gas convection heat transfer and physical
bombardment of solid heat receiver surfaces with millions of rapidly vibrating hot
solid particles. The furnaces take several forms.
Fig. 1.12. Circulating fluidized bed combustor
system (type 2 in earlier list).
24

25. The furnaces take several forms.
1. A refractory-lined container, with a fine grate bottom, filled with inert (usually refractory)
balls, pellets, or granules that are heated by products of combustion from a combustion
chamber below the grate. Loads or boiler tubes are immersed in the fluidized bed above
the grate for heat processing or to generate steam.
2. Similar to above, but the granules are fuel particles or sewage sludge to be incinerated.
The space below the grate is a pressurized air supply plenum. The fuel particles are ignited
above the grate and burn in fluidized suspension while physically bombarding the water
walls of the upper chamber and water tubes immersed in its fluidized bed.
3. The fluidized bed is filled with cold granules of a coating material (e.g., polymer), and
loads to be coated are heated in a separate oven to a temperature above the melting point
of the granules. The hot loads (e.g., dishwasher racks) are then dipped (by a conveyor)
into the open-topped fluidized bed for coating.
25

26. Furnace Classification by Fuel
 In fuel-fired furnaces, the nature of the fuel may make a difference in the furnace design, but that
is not much of a problem with modern industrial furnaces and burners, except if solid fuels are
involved.
 Similar bases for classification are air furnaces, oxygen furnaces, and atmosphere furnaces.
 Related bases for classification might be the position in the furnace where combustion begins,
and the means for directing the products of combustion, e.g., internal fan furnaces, high velocity
furnaces, and baffled furnaces.
 Electric furnaces for industrial process heating may use resistance or induction heating.
 Theoretically, if there is no gas or air exhaust, electric heating has no flue gas loss, but the user
must recognize that the higher cost of electricity as a fuel is the result of the flue gas loss from the
boiler furnace at the power plant that generated the electricity.
26

27.  Resistance heating usually involves the highest electricity costs, and may require circulating
fans to assure the temperature uniformity achievable by the flow motion of the products of
combustion (poc) in a fuel-fired furnace. Silicon control rectifiers have made input modulation
more economical with resistance heating. Various materials are used for electric furnace
resistors. Most are of a nickel–chromium alloy, in the form of rolled strip or wire, or of cast zig-
zag grids (mostly for convection). Other resistor materials are molten glass, granular carbon,
solid carbon, graphite, or silicon carbide (glow bars, mostly for radiation). It is sometimes
possible to use the load that is being heated as a resistor.
 In induction heating, a current passes through a coil that surrounds the piece to be heated. The
electric current frequency to be used depends on the mass of the piece being heated. The
induction coil (or induction heads for specific load shapes) must be water cooled to protect them
from overheating themselves. Although induction heating usually uses less electricity than
resistance heating, some of that gain may be lost due to the cost of the cooling water and the
heat that it carries down the drain.
27

28.  Induction heating is easily adapted to heating only localized areas of each piecen and to mass-
production methods. Similar application of modern production design techniques with rapid
impingement heating using gas flames has been very successful in hardening of gear teeth,
heating of flat springs for vehicles, and a few other high production applications.
 Many recent developments and suggested new methods of electric or electronic
heating offer ways to accomplish industrial heat processing, using plasma arcs, lasers, radio
frequency, microwave, and electromagnetic heating, and combinations of these with fuel
firing.
Furnace Classification by Recirculation
 For medium or low temperature furnaces/ovens/dryers operating below about 1400 F (760 C),
a forced recirculation furnace or recirculating oven delivers better temperature uniformity and
better fuel economy. The recirculation can be by a fan and duct arrangement, by ceiling plug
fans, or by the jet momentum of burners.
28

29. Figure 3.17 shows a batch-type direct-fired recirculating oven, and figure 1.13 illustrates the principle of
a continuous belt direct-fired recirculating oven. All require thoughtful circulation design and careful
positioning relative to the loads.
Fig. 3.17. Batch recirculating oven passes gases through the
loads many times, saving fuel. The circulating gases have
burner poc, and thus help uniformity.
29

30. Fig. 1.13. Continuous direct-fired recirculating oven such as that used for drying, curing,
annealing, and stress-relieving (including glass lehrs). The burner flame may need shielding
to prevent quenching with high recirculating velocity. Lower temperature ovens may be
assembled from prefabricated panels providing structure, metal skin, and insulation. To
minimize air infiltration or hot gas loss, curtains (air jets or ceramic cloth) should shield end
openings.
30

31. Furnace Classification by Direct-Fired or Indirect-Fired
If the flames are developed in the heating chamber proper, as in figure 1.1, or if the
products of combustion (poc) are circulated over the surface of the workload as in figure
3.17, the furnace is said to be direct-fired.
In most of the furnaces, ovens, and dryers shown earlier in this chapter, the loads were not
harmed by contact with the products of combustion.
Indirect-fired furnaces are for heating materials and products for which the quality of the
finished products may be inferior if they have come in contact with flame or products of
combustion (poc).
In such cases, the stock or charge may be (a) heated in an enclosing muffle (conducting
container) that is heated from the outside by products of combustion from burners or (b)
heated by radiant tubes that enclose the flame and poc.
31

32. Muffles. The principle of a
muffle furnace is sketched in figure
1.14. A pot furnace or crucible
furnace (fig. 1.15) is a form of
muffle furnace in which the
container prevents poc contact with
the load.
A double muffle arrangement is
shown in figure 1.16. Not only is
the charge enclosed in a muffle but
the products of combustion are
confined inside muffles called
radiant tubes. This use of radiant
tubes to protect the inner cover
from uneven heating is being
replaced by direct-fired type E or
type H flames to heat the inner
cover, thereby improving thermal
conversion efficiency and reducing
heating time.
32

33. Radiant Tubes. For charges that
require a special atmosphere for
protection of the stock from
oxidation, decarburization, or for
other purposes, modern indirect-
fired furnaces are built with a gas-
tight outer casing surrounding the
refractory lining so that the whole
furnace can be filled with a
prepared atmosphere.
Heat is supplied by fuel-fired
radiant tubes or electric resistance
elements.
Fig. 1.16. Indirect-fired furnace with muffles for both load and
flame. Cover annealing furnaces for coils of strip or wire are built
in similar fashion, but have a fan in the base to circulate a prepared
atmosphere within the inner cover.
33

34. Classification by Furnace Use (including the shape of the material to be heated)
 There are soaking pits or ingot-heating furnaces, for heating or reheating large ingots,
blooms, or slabs, usually in a vertical position.
 There are forge furnaces for heating whole pieces or for heating ends of bars for forging or
welding. Slot forge furnaces (fig. 1.1) have a horizontal slot instead of a door for inserting
the many bars that are to be heated at one time.
 The slot often also serves as the flue. Furnaces named for the material being heated include
bolt heading furnaces, plate furnaces, wire furnaces, rivet furnaces, and sheet furnaces.
 Some furnaces also are classified by the process of which they are a part, such as hardening,
tempering, annealing, melting, and polymerizing. In carburizing furnaces, the load to be
case-hardened is packed in a carbon-rich powder and heated in pots/boxes, or heated in
rotating drums in a carburizing atmosphere.
34

35. Classification by Type of Heat Recovery (if
any)
 Most heat recovery efforts are aimed at utilizing the
“waste heat” exiting through the flues.
 Some forms of heat recovery are air preheating, fuel
preheating, load preheating (Fig. 1.17), recuperative,
regenerative, and waste heat boilers.
 Preheating combustion air is accomplished by
recuperators or regenerators.
 Recuperators are steady-state heat exchangers that
transmit heat from hot flue gases to cold combustion air.
 Regenerators are non-steady state devices that
temporarily store heat from the flue gas in many small
masses of refractory or metal, each having considerable
heat-absorbing surface.
Fig. 1.17. Tool heating furnace with heat
recovering load preheat chamber.
35

36.  Then, the heat absorbing masses are moved into an incoming cold combustion air stream to
give it their stored heat.
 Furnaces equipped with these devices are sometimes termed recuperative furnaces or
regenerative furnaces.
 Regenerative furnaces in the past have been very large, integrated refractory structures
incorporating both a furnace and a checker work refractory regenerator, the latter often much
larger than the furnace portion. Except for large glass melter “tanks,” most regeneration is
now accomplished with integral regenerator/burner packages that are used in pairs.
 Boilers and low temperature applications sometimes use a “heat wheel” regenerator—a
massive cylindrical metal latticework that slowly rotates through a side-byside hot flue gas
duct and a cold combustion air duct.
 Both preheating the load and preheating combustion air are used together in steam
generators, rotary drum calciners, metal heating furnaces, and tunnel kilns for firing
ceramics.
36

37. Other Furnace Type Classifications
 There are stationary furnaces, portable furnaces, and furnaces that are slowly rolled
over a long row of loads.
 Many kinds of continuous “conveyor furnaces” have the stock carried through the heating
chamber by a conveying mechanism, some of which were discussed under continuous
furnaces.
 Other forms of conveyors are wire-mesh belts, rollers, rocker bars, and self-conveying catenary
strips or strands. In porcelain enameling furnaces and paint drying ovens, contact of the loads
with anything that might mar their surfaces is avoided by using hooks from an overhead chain
conveyor.
 For better furnace efficiency and for best chain, belt, or conveyor life, they should return within
the hot chamber or insulated space.
 “Oxygen furnace” was an interim name for any furnace that used oxygen-enriched air or near-
pure oxygen.
37

38.  In many high-temperature furnaces, productivity can be increased with miniumum
capital investment by using oxygen enrichment or 100% oxygen (“oxy-fuel
firing”).
 Either method reduces the nitrogen concentration, lowering the percentage of
diatomic molecules and increasing the percentage of triatomic molecules.
 This raises the heat transfer rate (for the same average gas blanket temperature
and thickness) and thereby lowers the stack loss.
 Oxygen use reduces the concentration of nitrogen in a furnace atmosphere (by
reducing the volume of combustion air needed), so it can reduce NOx emissions.
Such oxygen uses have become a common alteration to many types of furnaces,
which are better classified by other means discussed earlier.
38

39.  The heat exchanger, burner,
flue, ductwork, and
ventilation pipes are the
main parts of a furnace.
 Electric furnaces are
unique and feature a
contactor, sequencer, and
transformer.
 Gas furnaces have key
parts such as gas valves
and draft inducer motors
that electric furnaces don’t
have.
Parts of a Furnace System
39

40. Parts of a Furnace System
There are numerous parts of a furnace system that work together to create heat and deliver
it to your indoor spaces.
 Pilot light: In older furnaces, the pilot light burns constantly, ready to ignite the gas
when the furnace turns on to start the heating process.
 Thermocouple: The thermocouple detects a lit pilot light. When the thermocouple
senses a lit pilot light, it sends an electrical signal to the gas valve, signaling it to open
for gas flow.
 Hot surface ignitor: A newer technology, hot surface ignitors replace pilot lights in
newer furnace models. Electrical current is passed through the ignitor, raising its
temperature to start combustion when the gas supply turns on.
 Flame sensor: The flame sensor is a safety device that detects heat from the hot surface
ignitor. If no heat is detected, this device turns off the gas supply.
40

41.  Gas valve: The gas valve adjusts the pressure of natural gas coming into your
home, so it is appropriate for use in the furnace. It also controls the gas to the
furnace.
 Burners: A furnace’s burners mix gas and air to make a flame, which is the
furnace’s heat source.
 Heat exchanger: The heat exchanger holds toxic gases created when fuel burns.
Gases are safely vented away from your home while the heat exchanger gives off
heat to the surrounding air. This component looks like a collection of long, metal
tubing.
 Draft inducer motor: The draft inducer motor starts before gas begins to burn in
the furnace. Its job is to help push toxic combustion fumes out of your home’s vent
pipe by creating a vacuum.
41

42.  Pressure switch: The pressure switch ensures the draft inducer motor is
turned on to push fumes through the vent pipe. The vacuum created by the
draft inducer motor pulls at the pressure switch’s diaphragm to activate it and
allow gas flow – if the vacuum is not sensed by the pressure switch, gas is not
allowed into the furnace.
 Blower motor: The blower motor’s job is to push warm air created by the
furnace through the duct system and into the home.
 Blower motor capacitor: This component starts the blower motor, and some
keep the blower motor running at a consistent speed.
 Limit switch: The limit switch detects temperatures within the furnace. If the
furnace is too hot, the limit switch turns off the gas to prevent safety issues.
42

43. Blower Motor
43

44. Igniter and Pilot Light
44

45. Parts of an Electric Furnace
Like a gas furnace, electric furnaces have several different
components. While you may not need to be familiar with
every single part, you should be aware of the important
ones. That way, you’ll know exactly what to look for if your
furnace breaks down. An electric furnace can be broken
down into four main parts:
1.The Contactor: The contactor is essentially a control that
is used to get the voltage switched to your furnace heating
element. It works directly with your thermostat, meaning if
the thermostat doesn’t have a very high voltage, the
contactor will be energized by it. Once your thermostat is
satisfied with the temperature, the contactor shuts off by
opening the connection. The contactor is a crucial
component to keeping your home comfortable during the
winter season.
45

46. 46
2. The Heating Elements: The heating element inside an electric furnace consists of
several, tightly-wound metal coils. When your thermostat is turned on, electric relays
will begin the process of ignition. However, not all of the coils will heat up at once.
3. The Sequencer: On an electric furnace, a sequencer turns the heating elements on or
off. It controls when different sets of coils are permitted to heat. The reason why it does
not allow all of the coils to heat at once is because the power draw required would be
too large for your electrical system to handle. Electrifying the coils in a particular
sequence allows them to heat in a pattern, producing sufficient heat without
overloading the electrical panel.
4. The Transformer: The purpose of the transformer is to supply the power for the
furnace. It transfers all the electrical energy from one circuit to another. In an electric
furnace, you’ll have multiple currents that go through it.
Parts of an Electric Furnace

47.  Unlike the gas alternative, electric
furnaces do not have gas burners,
pilot lights, or hot surface igniters.
 Instead, the electrical ignition
system is what ignites the
furnace’s heating elements inside.
 As the electrical current passes
through the coils, the air absorbs
the heat created.
 Then, a blower motor distributes
the heated air through the ducts
and into your living area.
47

48. Additional Furnace Components
Ductwork
 While the ductwork isn’t exactly a part of
either a gas or electric furnace, it is an
essential component that allows your
home to be properly heated.
 Without ductwork, all the heated air that
is created inside of the furnace will not
be distributed throughout your home.
Also, without ductwork that is properly
sized, you will end up with rooms that
are either too color or too hot.
 Therefore, properly fitted and sized
ductwork is a crucial part that contributes
to the functionality of your entire furnace
system, whether it’s gas or electric.
48

49. Return Air Filters
 The return air filter is a
necessary component to keep
dust and debris from
getting inside of the
furnace.
 They should be inspected and
replaced frequently, as a dirty
air filter will prevent the unit
from functioning properly.
49

50. The Thermostat
 The thermostat measures the temperature inside of
your home and by setting it, it communicates with
your igniter to turn on. It is essentially used
to control the temperature in your home. You can
use the thermostat to adjust the temperature in your
home, based on your desired comfort level.
 By turning the temperature on the thermostat up, the
flame of the gas burner will get larger to increase the
temperature in your home. On the other hand, when
you turn the thermostat down, the flame will shrink
to lower the temperature in your living spaces. The
thermostat “speaks” to the heating elements on
electric furnaces to control the heat dispersed.
50