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Codes, regulations, and laws regarding wood-heating,
gas appliances, and components change frequently. It is
essential that you be familiar with the appropriate cur-
rent National Fire Protection Association (NFPA) infor-
mation and other codes, regulations, and laws.
OBJECTIVES
After studying this unit, you should be able to
list reasons for the formation of creosote.
describe methods to help prevent the formation of
creosote.
explain how stovepipe should be assembled andinstalled.
list safety hazards that may be encountered with wood
stoves.
describe the three types of venting for gas stoves.
explain how a fireplace insert can improve on the
heating efficiency of a fireplace.
describe the difference between passive and active
solar systems.
describe the declination angle and the effect it has on
the suns radiation during winter and summer.
list the typical components in a liquid-based solar
system and describe the function of each.
describe the operation of a solar domestic hot watersystem.
describe a swimming pool solar-heating system.
SAFETY CHECKLIST
Many safety practices must be adhered to when
installing or using a wood-burning appliance. Many of
these safety practices are stated within this unit, printed
in red. Many other safety practices must be adhered to
including those provided by manufacturers and local,
regional, and state codes. It is also necessary to use good
judgment and common sense at all times.
If an antifreeze solution is used in a solar domestic hot
water system, a double-walled heat exchanger must be
used.
A.1 WOOD-BURNING STOVES
Stoves are used as an alternative heating appliance in many
homes. Some homes use stoves as a primary heat source, and
others use them to supplement primary heat sources. Both
wood- and gas-burning stoves are used. Wood must be read-
ily available to make the use of wood-burning stoves prac
cal. However, pellet stoves, which burn small compresse
wood by-products, may be used in many locations where pe
lets are available.
A.2 ORGANIC MAKEUP ANDCHARACTERISTICS OF WOOD
Wood plants manufacture glucose. Some of this glucose,
sugar, turns into cellulose. Approximately 88% of wood
composed of cellulose and lignin in equal parts. Cellulose
an inert substance and forms the solid part of wood plants.
forms the main or supporting structure of each cell in a treLignin is a fibrous material, a polymer, which binds to cell
lose fibers and hardens and strengthens the cell walls
trees. The remaining 12% of the wood is composed of resin
gums, and a small quantity of other organic material.
Water in green or freshly cut wood constitutes from o
third to two thirds of its weight. Thoroughly air-dried woo
may have as little as 15% moisture content by weight.
Wood is classified as hardwood or softwood. Hickor
oak, maple, and ash are examples of hardwood. Pine an
cedar are examples of softwood. Figure A1 lists some common types of wood and the heat value in each type in m
lions of Btu/cord. A cord of wood can be split, unsplit,
mixed. It is important to know whether the wood is split, bcause there is more wood in a stack that is split. Wood is so
Alternative Heating (Stoves,Fireplace Inserts, Solar)A
UNITUNIT
A
Figure A1 The table indicates the weight per cord, the Btu percord of air-dried wood, and the equivalent value of No. 2 fuel oil in
gallons. Courtesy Yukon Energy Corporation
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by the cord, which is a stack 4 ft 4 ft 8 ft or 128 ft3. Be-
cause wood is sold by volume and not by weight, wood that
is split has less air space between the individual pieces. This
will give the cord of wood a higher density, meaning more
wood per cord.
Wood should be dry before burning. Approximately 20%
more heat is available in dry wood than in green wood. Wood
should be stacked off the ground on runners and should be
well ventilated, Figure A2. When possible, the wood shouldbe covered, but air should be allowed to circulate through it.
Wood splits more easily when it is green or freshly cut and
dries better when it has been split. When green wood is
burned, combustion will be incomplete, resulting in un-
burned carbon, oils, and resins, which leave the fire as
smoke.
During oxidation or burning, oxygen is added to the
chemical process. This actually turns wood back into prod-
ucts that helped it grow as a plant: primarily carbon dioxide
(CO2), water (H
2O), and other miscellaneous materials. Heat
also is produced. Some woods produce more heat than oth-
ers per cord, Figure A1. Generally, dry hardwoods are themost efficient.
A.3 ENVIRONMENTAL PROTECTIONAGENCY (EPA) REGULATIONS
On July 1, 1988, the Environmental Protection Agencys first
national woodstove emissions standards went into effect.Emissions from wood-burning appliances were adding to the
pollutants in the air along with all the other sources of air pol-
lutants. C Wood smoke contains both polycyclic organicmatter (POM) and nonpolycyclic organic matter, which are
considered to be health hazards and are of concern to many
people.CAll wood-burning stoves manufactured after July1, 1989, must be EPA certified. Two EPA standards exist
one for catalytic stoves and one for noncatalytic stoves. Cat-
alytic stoves contain a catalytic combustor and may not emit
more than 5.5 g/h of particulates for those stoves manufac-
tured between July 1, 1989, and June 30, 1990. The noncat-
alytic stoves manufactured between these dates may not emit
more than 8.5 g/h. These limits are reduced further for those
stoves manufactured after July 1, 1990, to 4.1 g/h for the cat-
alytic models and 7.5 for the noncatalytics. As new stoves are
purchased and installed, replacing older stoves, the air pollu-
tants from wood-burning stoves will be reduced drastically,
because the particulate emission of the catalytic stove is ap-
proximately 10% of the emissions of the older stoves.
A.4 CREOSOTE
Creosote is a mixture of unburned organic material. When it
is hot, it is a thick dark-brown liquid. When it cools, it forms
into a residue like tar. It then often turns into a black, flaky
substance that adheres to the inside of the chimney or stove-
pipe. The formation of creosote is particularly a problem
with the uncertified stoves manufactured before July 1,
1989. Some of the primary causes of excessive creosote are:
smoldering low-heat fires.
smoke in contact with cool surfaces in the stovepipe or
chimney.
burning green wood. burning softwood.
SAFETY PRECAUTION: Creosote buildup in the stovepipe and
chimney is dangerous. It can ignite and burn with enough
force to cause a fire in the building. Stovepipes have been
known to be blown apart, and chimney fires are common
with this excessive buildup.
To help prevent the formation of creosote, burn dry hard-
wood. Fires should burn with some intensity. When the
stovepipe or chimney flue temperature drops below 250F,
creosote will condense on the surfaces. Use as little run of
stovepipe as possible. The minimum rise should be 1/4 in. per
ft of horizontal run. A rise of 30 is recommended, FigureA3. Anything that slows the movement of the gases allows
2 Refrigeration and Air Conditioning Technology
1 CORD OF WOOD
8 ft
4 ft
4 ft
Figure A2 Wood should be stacked on runners so that air cancirculate through it.
FLUSH WITHINSIDE OFFLUE LINER.
STOVEPIPE SHOULDRISE FROM STOVE
TO CHIMNEY (1/4" RISEPER FOOT IS THE MINIMUM
RECOMMENDED).
KEEP RUN ASSHORT ASPOSSIBLE.
CHIMNEY FLUE
Figure A3 The stovepipe should rise from stove to chimney.
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them to cool, which will cause more creosote condensation.Stovepipes and chimneys should be cleaned regularly.
Assemble the stovepipe with the crimped end down,
Figure A4. This will keep the creosote inside the pipe.
A.5 DESIGN CHARACTERISTICS OFWOOD-BURNING STOVES
As mentioned earlier, all wood-burning stoves manufactured
since July 1, 1989, must be EPA certified. These may be cer-
tified as noncatalytic or catalytic combustor stoves.
Noncatalytic Certified StovesThese stoves force the unburned gases to pass through a sec-
ondary combustion chamber. Temperatures higher than
1000F are maintained in this chamber, burning the gases.
This burns the pollutants, including most of the creosote, and
produces more heat, providing a better stove operating effi-
ciency. Figure A5 is an example of one design of this typeof stove.
Catalytic Combustor Certified Stoves
The catalytic combustor is a form of afterburner that in-
creases the burning of wood by-products. These combustorsuse a catalyst to cause combustion by producing a chemical
reaction, which burns the flue gases at about 500F rather
than the 1000F otherwise required.
Most combustors are a cell-like structure, Figure A6, andconsist of a substrate, washcoat, and catalyst. The substrate
is a ceramic material formed into a honeycomb shape. Ce-
ramic material is used because of its stability in extremely
cold and hot conditions. The washcoat, usually made of an
aluminum-based substance called alumina, covers the ce-
ramic material and helps disperse the catalyst across the com-
bustor surface. The catalystis made of a noble metal, usually
platinum, palladium, or rhodium, which is chemically stab
in extreme temperatures. Figure A7 is an illustration ofwoodstove with a catalytic combustor. A disadvantage of th
combustor is that it must be replaced every few years.
Radiation and Convection Characteristics
Wood-burning stoves heat by both radiation and convectio
Radiation is heat that comes from the stove in waves an
heats objects in its path, such as the walls, floor, and furn
ture. The stove also heats the air around it. This is called co
vective heat. As the air is heated, it rises, and cooler a
comes in to take its place, and it is heated. The cycle conti
ues, and the currents are referred to as convection curren
Some stoves are designed to utilize the convective heating
a greater extent than others. These stoves may have a blow
Unit A Alternative Heating (Stoves, Fireplace Inserts, Solar)
CRIMPEDEND DOWN
CREOSOTE WILLRUN DOWNSTOVEPIPETO STOVE.
CREOSOTE WILLLEAK OUTAROUND JOINT.
CRIMPEDEND UP
WRONGRIGHT
Figure A4 The stovepipe should be assembled with the crimpedend down so that creosote will not leak out of the joint.
Figure A5 A noncatalytic wood-burning stove. CourtesyHearthStone NHC, Inc.
CATALYST
WASHCOAT
SUBSTRATE
MAGNIFIED SECTION
LENGTH
DIAMETER
CELL DENSITY(NUMBER OF COPENINGS PERSQUARE INCH)
Figure A6 A catalytic combustor element. Courtesy of CorningInc.
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system to spread the heat out further and to make the con-
vection process more efficient.
Pellet Stoves
Pellet stoves are a more recent design, are energy efficient,
and use a renewable energy source, Figure A8. The fuel con-sists of small compressed pellets made from waste wood, pri-
marily sawdust from lumber sawmills. However, the pellets
may be made from waste cardboard or even agricultural
wastes such as sunflower and cherry seed hulls. Stove own-ers should be sure that only the type of pellets recommended
by the manufacturer are used. They are normally provided in
40- or 50-lb bags.
Most pellet stoves are designed with a hopper at the back
or top. The pellets are fed to the combustion chamber with an
auger powered by an electric motor, which is often con-
trolled with a thermostat. The room air is generally circulated
through the heat exchanger and into the conditioned space by
a multispeed blower.
Very little air pollution is produced with as little as 1%
of the pellet material remaining as ash. Most stoves do not
require a chimney because exhaust gases are forced outsidethrough a vent pipe by a combustion fan. Combustion air
may be drawn in from outdoors so that heated room air is
not used for combustion. This provides additional effi-
ciency by not creating a negative pressure in the room thus
decreasing the cold air that will infiltrate through cracks in
doors and windows. Venting of exhaust gases may be
through a horizontally positioned vent pipe with an end cap
to prevent wind from blowing air and the exhaust gases into
the stove, Figure A9. This horizontal vent pipe must beconstructed of PL vent pipe tested to UL 641 standards. It
is a double-walled pipe with an air space between the walls.
All joints must be sealed with an approved sealer. This is
important because this venting system has an electrically
operated exhaust combustion fan; if there should be a
power failure, the combustion fumes could enter the condi-
tioned space.
A lined masonry chimney that meets all appropriate codes
may be used. However, many masonry chimneys will be
large enough to affect the operation of pellet stoves ad-
versely. These chimneys may be relined with a stainless steel
liner, Figure A10. Consult the stove manufacturers litera-ture for the recommended diameter for these liners.
4 Refrigeration and Air Conditioning Technology
WOOD
THERMALINSULATION
FLUE
SECONDARY AIRDISTRIBUTOR
ADJUSTABLEPRIMARYAIR SUPPLY
Figure A7 An illustration of a woodstove with a catalyticcombustor. Courtesy of Corning Inc.
Figure A8 A pellet stove. Courtesy Vermont Castings
Figure A9 A horizontal vent pipe must have an end cap to preventair or exhaust gases from being blown into the stove. A vent pipe may
be extended vertically above the eaves. Courtesy Vermont Castings
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Stove Construction
Stoves may be constructed of steel, cast iron, soapstone, or a
combination of these materials. Stoves made of steel are nor-
mally the least expensive. They are made of sheet steel
welded together normally with a firebox of refractory bricks.
These stoves give off heat almost immediately after the fire
is started. With a large, hot fire, they will quickly give off a
considerable amount of heat. However, when the fire dies,the heat from the stove will also quickly cool.
Many stoves are manufactured of cast iron. These stoves
can be much more decorative, because the casting process
provides an opportunity for intricate detail particularly on
the sides and legs, Figure A11. Cast iron is more durablethan steel, and the heat is more even and less intense than that
of a sheet-steel stove. These stoves also cool down more
slowly after the fire dies down or goes out.
Soapstone may be used, particularly in combination with
cast iron, as a material in the manufacture of wood-burning
stoves, Figure A12. Soapstone can withstand the changes intemperature such as from room temperature to very intense
heat. It may be used not only on the exterior of stoves, butalso may be used for the firebox, because it can withstand ex-
posure to direct flames. This material provides a gentle heat
and can hold and radiate heat for longer periods than the
other materials.
Makeup Air
Air used in combustion must be made up or resupplied from
the outside, for example, with an inlet from outside directly
to the stove, Figure A13. Often an older home has many airleaks. The hot air may leak out near the ceiling or through the
Unit A Alternative Heating (Stoves, Fireplace Inserts, Solar)
Figure A10 Pellet stoves may operate more efficiently if masonrychimneys are relined with a stainless steel liner. Courtesy Vermont
Castings
Figure A11 A wood-burning stove made from cast iron. CourtesMajestic Products Co., Huntington, IN
Figure A12 A wood-burning stove made with soapstone.Courtesy HearthStone NHC, Inc
DAMPER
FRESH AIR INLETFROM OUTSIDE
Figure A13 A stove with a fresh air tube entering it from outside
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attic. Cool air can leak in through cracks around windows,
under doors, and elsewhere. Although this may disturb the
normal heating cycle, it does help to make up air for that air
leaving the chimney as a result of the combustion and vent-
ing. SAFETY PRECAUTION: In modern homes that are sealed
and insulated well, some provision may have to be made to
supply the makeup air. A door may have to be opened a crack
to provide a proper draft. A stove could actually burn enough
oxygen in a small home to make it difficult to get enough oxy-gen to breathe. Always make sure that there is enough
makeup air.
Safety Hazards
SAFETY PRECAUTION: Live coals in the stove in the living
area of a house, along with creosote in stovepipes and
chimneys, make it absolutely necessary to install, main-
tain, and operate stoves safely. This cannot be empha-
sized enough.
Following are some of the safety hazards that may be en-
countered:
A hot fire can ignite a buildup of creosote, resulting in a
stovepipe or chimney fire.
Radiation from the stove or stovepipe may overheat
walls, ceilings, or other combustible materials in the
house and start a fire.
Sparks may get out of the stove, land on combustible
materials, and ignite them. This could happen through a
defect in the stove, while the door is left ajar, while the
firebox is being filled, or while ashes are removed.
Flames could leak out through faulty chimneys, or heat
could be conducted through cracks to a combustible
material.
Burning materials coming out of the top of the chimneycan also start a fire at the outside of the house. These sparks
or glowing materials can ignite roofing materials, leaves,
brush, or other matter outside the house.
A.6 INSTALLATION PROCEDURES
A national testing laboratory should approve a wood-burning
stove or appliance. Before installing a stove, stovepipe, or
prefabricated chimney, be sure that all building and fire mar-
shals codes are followed, as well as the instructions of the
testing laboratory and manufacturer. If one code or set of in-
structions is more restrictive than another, follow the most
restrictive instructions.These instructions should include the distance the stove
should be located from any combustible material, such as a
wall or the floor. They should indicate the minimum required
protective material between the stove and the wall and be-
tween the stove and the floor. Excessive heat from the stove
can heat the walls or floor to the point where a fire can be
started.
The stove must be connected to the chimney with an ap-
proved stovepipe, often called a connectorpipe. Codes and
instructions must be followed.
A stove collar adapter often supplied by the manufac-
turer should be used to install the stovepipe to the stove,
Figure A14. The manufacturer may provide a special pro-vision for this.
Figure A15 shows three different types of installations.The stovepipe must not run through any combustible mater-
ial, such as a ceiling or wall. Approved chimney sections
with necessary fittings should be used. Figure A16 illus-
trates details for adapting the stovepipe to the through-the-wall chimney fittings. Remember to keep horizontal
stovepipe runs to a minimum. A rise of 1/4 in. per ft should
be considered a minimum, Figure A3. Local codes or man-ufacturers may require a greater rise. Be sure that approved
thimbles, joist shields, insulation shields, and other neces-
sary fittings are used where required. Ensure that a recog-
nized national testing laboratory approves all materials and
that all codes are met.
Only one stove can be connected to a chimney. For ma-
sonry chimneys with more than one flue, no more than one
stove can be connected to each flue. A factory-built chimney
used for woodstoves should be rated as a residential and
building heating appliance chimney. Check all codes.
SAFETY PRECAUTION: Many stoves are vented through ma-
sonry chimneys. If a new chimney is being used, it should
have been constructed according to applicable building
codes and carefully inspected. If an old chimney is being
used, an experienced person should inspect it to ensure that
it is safe to use. The mortar in the joints may be deteriorated
and loose, or a serious chimney fire may have cracked the
chimney. All necessary repairs should be made to the chim-
ney by a competent mason before connecting the stove to it.
Manufacturers or their suppliers may recommend that chim-
neys be lined, Figure A10. This may be recommended for a
better draft and/or safety.
6 Refrigeration and Air Conditioning Technology
USE ALL THREESPECIAL SCREWS.
Figure A14 A stove collar adapter for double-wall stovepipe.
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A.7 SMOKE DETECTORS
SAFETY PRECAUTION: Smoke detectors should be used in
homes regardless of the type of heating appliance used. It
even more important to install smoke detectors when bur
ing wood fuel. Many types of detectors are available. Thes
may be AC-powered photoelectric type or an AC- or batter
powered ionization chamber type.
A.8 GAS STOVES
Gas stoves are becoming popular as a heating appliance. Th
American National Standards Institute (ANSI) may certi
these as a decorative appliance or as a room heater. De
orative appliances are attractive but not designed for larg
space heating. Room heaters are, as the name implies, hea
ing appliances and will have efficiency ratings. These stov
may be manufactured of materials similar to woodstoves an
are available in many attractive colors, Figure A17.
Unit A Alternative Heating (Stoves, Fireplace Inserts, Solar)
ROUND CAP
PIPE
STOVEPIPE
STOVEPIPE
STOVEPIPE
WALLTHIMBLE
ROUNDSTORM
COLLAR
ROUND
FLASHING
PIPE
WALL SUPPORTWITH CLEAN OUT
NOTE: OUTSIDE CHIMNEYS ARE NOT ASDESIRABLE, SINCE THEY ARE MORESUBJECT TO DOWNDRAFTS AND
CREOSOTE BUILDUP.
CHIMNEY MUST BE ENCLOSED WHERE IT PASSES THROUGH
OCCUPIED SPACES TO MAINTAIN REQUIRED CLEARANCES
TO COMBUSTIBLES AND TO PROTECT AGAINST DAMAGE.
TEEASSEMBLY
ROUND CAP
OPEN BEAM CEILINGINSTALLATION USING
ROOF SUPPORT
EXTERIOR WALL INSTALLATIONUSING WALL SUPPORT, BRACKETS,
AND THROUGH-THE-WALL TEE
STANDARD INSTALLATIONUSING CEILING SUPPORT
PIPE
ROUND CAP
ROUNDSTORM COLLAR
ROUNDSTORM COLLAR
ROUND
FLASHING
ROUND
FLASHING
ATTICINSULATIONSHIELD
FIRESTOP ASSEMBLY
CEILING SUPPORTASSEMBLY
ROOFSUPPORT
ASSEMBLY SUPPORTBRACKETASSEMBLY
Figure A15 Three different types of stove installations.
CHIMNEY TEE BRANCH EXTENSION
CHIMNEY TEE PIPE END PLATE
CHIMNEYCONNECTOR RING
18-INCHDOUBLE-WALL
BLACK STOVEPIPEADJUSTABLE LENGTH
24-INCHDOUBLE-WALL
BLACK STOVEPIPEPIPE SECTION
STOVE COLLARADAPTER
CHIMNEYPIPESECTIONCHIMNEYTEE
CHIMNEY
TEE WALLSUPPORT
TYPICALINSTALLATION
USING90 ELBOW
WITHTHROUGH-THE-WALL
CHIMNEY TEE
WALLTHIMBLE
90 ELBOW
Figure A16 Details of a through-the-wall installation.
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These stoves may be designed to burn natural or propane
gas. Many are designed so the orifice can be adjusted or
changed to switch from burning one gas to the other. Most
utilize a standing pilot for ignition and have controls to shut
off the gas should the pilot be out. Many of these stoves op-
erate without electricity and can be used for heating during a
power outage. Some have variable-speed convection blow-
ers to help circulate the heated air.
VentingThese gas stoves may be designed asB-vent, direct-vent, or
vent-free stoves.
B-VENT. Stoves requiring a B-vent must be vented throughthe roof or into an existing chimney. Aflue liner may be sug-
gested or required if venting into an existing chimney. The
liner will reduce the size of the flue so that the stove will draft
properly.
DIRECT-VENT. Stoves utilizing a direct-vent system use adouble-wall pipe to pull outside air in for combustion and to
vent flue gases to the outside. Direct-vent options mayinclude:
venting straight back from the stove and through the
wall.
venting up from the stove and then through the wall.
venting up through the roof.
in some cases venting into a lined fireplace flue.
VENT-FREE. Vent-free stoves, as the name implies, requireno venting. Some people are concerned about gas combus-
tion in the living area and not venting the flue gases. These
stoves do have a good safety record but are not approved at
this writing in all states. They have an oxygen depletion
sensor (ODS), which turns off the pilot light and gas supply
when the oxygen level in the area of the stove is depleted to
a certain level.
Gas appliances should be installed by certified personnel
or by those approved in that region to do so.
A.9 FIREPLACE INSERTSFireplace inserts can convert a fireplace from a very inefficientheat source to one that is more efficient. Very little heat can be
obtained from a fireplace without some device to help contain
the heat and to move heat from the fireplace into the room. The
fireplace insert provides a way to retain the heat and blow it
into the room. Figure A18 is a photo of a fireplace insert.
Wood-Burning Inserts
Awood-burning insert is basically a woodstove that is designed
to be placed into an existing fireplace. Fireplace inserts can be
either wood- or gas-burning. New wood-burning inserts must
be certified by the EPA as woodstoves are. This makes them
more clean burning and more efficient. For a wood-burning in-
sert to be used, the fireplace and chimney must generally be of
masonry construction. Local building codes and the manufac-
turers specifications for the particular insert should be con-
sulted to ensure that the size and construction of the fireplace
would accommodate the insert. All installations should meet
the NFPA and other appropriate codes. Many factory-built or
prefabricated fireplaces are not approved for inserts.
Inserts are usually made from plate steel, cast iron, or a
combination of these materials. They may fit into the fire-
place opening so that they are basically flush with the front,
or they may protrude to some degree onto the hearth. Thosethat protrude are usually more efficient as this part of the in-
sert will provide more radiant heat. Inserts normally have
blowers that may be controlled manually or with a thermo-
stat and which improve the efficiency.
Codes now in many areas for new insert installations re-
quire that the insert be installed with a positive connection to
the chimney flue, which prevents creosote from running down
8 Refrigeration and Air Conditioning Technology
Figure A17 A gas stove. Courtesy of Majestic Products Co.,Huntington, IN
Figure A18 A wood-burning fireplace insert. Courtesy of MajesticProducts Co., Huntington, IN
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into the fireplace, causing a fire hazard. Smoke and gases then
exit the fireplace more directly into and out of the chimney.
Before an insert is installed, a professional should inspect
the chimney. If there is creosote buildup, the chimney must
be cleaned. The chimney and fireplace should be checked for
cracks or flaws that could be a fire hazard. Inserts should
never be used in a chimney flue used for another purpose.
Many inserts make it more difficult to clean the chimney,
as they must be removed from the fireplace. Some insertshave a special collar and direct flue liner to the top of the
chimney, and these may be left in place for cleaning. Pro-
fessional chimney sweeps should be employed to clean
chimneys.
Gas Fireplace Inserts
These inserts may be used to convert an existing wood-
burning fireplace to a gas appliance. Many of these may be in-
stalled in prefabricated fireplaces where wood-burning units
may not. They may be designed to burn either natural gas or
propane but usually need to be adjusted for one or the other.
Before installing any insert, ensure that the existing fireplace
and chimney are approved for the insert chosen to be installed.
Many of these units and/or installations require that the
chimney flue be lined with a metal liner and connected to the
insert. This produces a better draft and more efficiency.
These inserts are usually sealed with glass doors and have
blowers that help to make them more efficient. The doors
prevent excess indoor air from being used for combustion.
Just the right amount of combustion air is usually introduced
through adjustable air shutters. Blowers simply make the
convective heat transfer more efficiently. NFPA and other
codes should be consulted regarding these liners.
Some newer gas inserts are designed so that they do notneed a chimney liner. They are less efficient and allow more
heat up the chimney, which heats the existing chimney flue
liner and increases the draft.
All gas appliances, stoves, or inserts must be connected to
the gas source. Piping needs to be routed and installed. This
usually means cutting, threading, and sealing pipe and should
be done by a professional trained and approved to do this work.
A.10 SOLAR HEATING
The sun furnishes the earth with tremendous amounts of di-
rect energy each day. It is estimated that 2 weeks of the suns
energy reaching the earth is equal to all of the known de-posits of coal, gas, and oil. The challenge facing scientists,
engineers, and technicians is to better harness and use this
energy. We know that the sun heats the earth, which heats the
air immediately above the earth. One of the challenges is to
learn how to collect, store, and distribute this heat to provide
heat and hot water for homes and businesses. Many advances
have been made, but the design and installation of solar sys-
tems has progressed very slowly. It is assumed, however, that
as the resources are further depleted and as economics or po-
litical actions cause energy crises, it will be only a matter of
time before direct energy of the sun is used extensively.
A.11 PASSIVE SOLAR DESIGN
Many structures being built presently are usingpassive sol
designs. These designs use nonmoving parts of a building
structure to help provide heat or cooling, or they elimina
certain parts of a building that help cause inefficient heati
or cooling. Some examples follow:
In areas where there are harsh winters, more windows
can be placed on the east, south, or west sides ofhomes and fewer on the north side. This allows
warming from the morning sun in the east and from th
sun throughout the rest of the day from the south and
west. By eliminating windows on the north side, this
coldest side of the house can be better insulated.
Place greenhouses, usually on the south side, to collec
heat from the sun to help heat the house, Figure A19 Design roof overhangs to shade windows from the su
in the summer but to allow sun to shine through the
windows in the winter, Figure A20.
Unit A Alternative Heating (Stoves, Fireplace Inserts, Solar)
Figure A19 A greenhouse will allow the sun to shine into thehouse. It may also have a masonry floor, or barrels of water may be
located in the greenhouse to help store the heat until evening whenthe sun goes down. This heat then may be circulated throughout the
house.
WINTER SUN
SUMMER SUN
Figure A20 An overhang may be constructed to allow the sun toshine into the house in the winter when it is lower in the sky and ye
shade the window in the summer.
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Provide a large mass such as a concrete or brick wall to
absorb heat from the sun and temper the inside
environment naturally.
Place latent-heat storage tubes containing phase-
change materials where they can collect heat to be
released at a later time, Figure A21.The remainder of this unit is limited to a discussion ofac-
tive solar systems. These systems use electrical or mechani-
cal devices to help collect, store, and distribute the suns
energy. The distribution of this heat to the conditioned spaceis by means of the same type of equipment used in fossil-fuel
furnaces.
A.12 DIRECT AND DIFFUSE RADIATION
The sun is a star often called the daystar. A very small
amount of the suns energy reaches the earth. Much of the en-
ergy that does reach the earths atmosphere is reflected into
space or absorbed by moisture and pollutants before reach-
ing the earth. The energy reaching the earth directly is direct
radiation. The reflected or scattered energy is diffuse radia-
tion, Figure A22.
A.13 SOLAR CONSTANT ANDDECLINATION ANGLE
The rate of solar energy reaching the outer limits of theearths atmosphere is the same at all times. It has been de-
termined that the radiation from the sun at these outer lim-
its produces 429 Btu/ft2/h on a surface perpendicular (90)
to the direction of the suns rays. This is known as the
solar constant. The energy from the sun is often called
insolation.
The earth revolves once each day around an axis that
passes through the north and south poles. This axis is tilted
23.5, so the intensity of the suns energy reaching the north-
ern and southern atmospheres varies as the earth orbits
around the sun. This tilt or angle is called the declination an-
gle and is responsible for differences during the year in the
distribution of the intensity of the solar radiation, FigureA23.
10 Refrigeration and Air Conditioning Technology
Figure A21 Latent-heat storage tubes may be placed in windows
where heat is stored when the sun is shining. Courtesy of CalorthermAssociates
CLOUDS(SCATTERING ANDABSORPTION)
ATMOSPHERE(ABSORPTION)
DIRECTRADIATION
UPPER ATMOSPHERE
EARTH
DUST(SCATTERING)
Figure A22 Radiation striking the earth directly from the sun is considered direct radiation. If it reaches the earth after it has been deflected byclouds or dust particles, it is called diffuse radiation.
DECLINATIONANGLE
EARTH
WINTER
WINTER
SUMMER
+23.5
23.5
SUMMER
DECLINATIONANGLE
SUN
Figure A23 The angle of declination (23.5) tilts the earth so thatthe angle from the sun north of the equator is greater in the winter.
The suns rays are not as direct, and the normal temperatures are
colder than during the summer.
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The amount of radiation reaching the earth also varies ac-
cording to the distance it travels through the atmosphere. The
shortest distance is when the sun is perpendicular (90) to a
particular surface. This is when the greatest energy reaches
that section of the earth, Figure A24. The angle of the sunsrays with regard to a particular place on the earth plays an
important part in the collection of the suns energy.
A.14 ACTIVE SOLAR DESIGN
The systems discussed and illustrated in this unit are basic
systems with a minimum of controls, check valves, pressure
relief valves, and other safety protection included. Manufac-
turers instructions and local and state codes must be fol-
lowed when installing equipment.
Active solar design utilizes collectors, storage systems,
distribution devices such as pumps and fans, and control sys-
tems. These solar systems are used primarily for space heat-
ing, domestic hot water, and swimming pool heating.
Liquid Solar Forced AirSpace-Heating Systems
Figure A25 illustrates a basic water drain-down liquspace-heating system, which also includes a domestic h
water tank. Drain-down systems are one type of system us
in areas where water to and from and in the collectors wou
freeze if left in the system. When collectors are producin
heat at a higher temperature than the storage water, circultor pump A moves water from the storage to be heated a
from the collectors back to storage. When the house therm
stat calls for heat, circulator pump B moves water from sto
age to the heat exchanger in the furnace duct. The furnace fa
blows air across the heat exchanger, warming the air, and di
tributes it to the house. Also shown is a domestic hot wat
tank heated through a heat exchanger in the water storag
When circulator pump A shuts down, the collector water w
all drain to a heated area to keep the water from freezing
cold weather. Note that the pipe from the collector into th
storage tank does not extend into the water. This provid
venting and allows the collectors and piping to drain. If th
space is not provided, other venting in the collector system
necessary.
An alternative design that is often preferred, particular
in colder climates, requires a closed-collector piping syste
using an antifreeze solution instead of water, Figure A2This figure illustrates a closed liquid collection to a wat
storage system with air distribution to the house. The liqu
in the collector system is an antifreeze and water solution.
is heated at the collectors and pumped through the coil at th
heat exchanger and back to the collectors. This continues
long as the collectors are absorbing heat at a predetermine
temperature.
When the room thermostat is calling for heat, thre
way valve 1 allows the water to be circulated by pump
through the liquid-to-air heat exchanger and back to th
Unit A Alternative Heating (Stoves, Fireplace Inserts, Solar)
EARTH'S SURFACE
ATMOSPHERE90
POINT 1
POINT 2
POINT 3
Figure A24 Radiation from the sun will be warmer at point 1 as ittravels the shortest distance through the atmosphere.
COLLECTOR PANELS
ROOMTHERMOSTAT
HOTWATER
TANK
LIQUID-TO-AIRHEAT EXCHANGER
HEATEXCHANGER
STORAGE TANKCIRCULATOR PUMP
PUMP
CONTROLLER
PUMP
AIR INTAKE
BA
Figure A25 Collectors use water as the liquid. This is a drain-down system because the water in the collectors would freeze on cold nights.
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liquid-to-liquid heat exchanger, where it absorbs more heat.
If the room thermostat is not calling for heat, three-way valve
1 diverts the water to storage. If the storage temperature has
reached a predetermined temperature, the collector solution
is circulated through the purge coil. The solution is diverted
to this purge coil through three-way valve 2. (The heat is dis-
sipated into the air outside through this coil.) This is a nec-
essary safety precaution because it is possible for the
collector system to overheat and damage the equipment.
Note that a liquid-to-liquid heat exchanger is used to heat
the storage water. The collector antifreeze fluid must be kept
separated from the storage water. This system is less efficient
than the drain-down system, which does not require the ex-
tra heat exchanger.
In most areas an auxiliary heating system is required to
provide comfort heating at all times. A conventional hot airheating system can be used in the same duct used for the so-
lar system. Room thermostats in each system may be used to
provide steady comfortable heat.
Liquid Collection/Water Storage/AuxiliaryConventional Hot Water Boiler
A liquid-based solar collector system may be paired with a
hot water finned-tube convector heating furnace. The col-
lector system can be of the same design as an air distribu-
tion system. It can be a drain-down water design or one that
uses antifreeze in the collectors with a heat exchanger in the
storage unit. Solar collector and storage temperatures maybe lower than those produced by a hot water boiler. This can
be compensated forto some extentby using more fin
tubing than would be used with a conventional hot water
system.
Figure A27(A) illustrates a design using a liquid-basedsolar collector with a hot water boiler system. This design
uses the auxiliary boiler when the storage water is not hot
enough. If the solar storage is hot enough, the boiler does
not operate. Water is pumped from the storage tank and by-
passes the boiler. It goes directly to the baseboard fin tubing.
The three-way diverting valve automatically causes this
boiler bypass. When auxiliary heat is called for, the 2 three-
way diverting valves cause the water to bypass the storage.
It would be very inefficient to pump heated water through
the storage tank.
A system can be designed as two separate systems in par-
allel as in Figure A27(B). These separate systems can bothbe operated at the same time. With this design, the solar sys-
tem can help the auxiliary system when the temperature of
the storage water is below that which would be satisfactory
for it to operate alone. Sensors are used in either system to
tell the controller when to start and stop the pumps and when
to control the diverting valves.
A.15 SOLAR RADIANT HEAT
Figure A28 illustrates a water storage, radiant heating sys-tem with an auxiliary hot water boiler. Either water or an an-tifreeze solution is piped through a collector system and in
the case of an antifreeze solution, through a heat exchanger
in the water storage. The heating coils may be imbedded in
concrete in the floor or in plaster in ceilings or walls. The
normal surface temperature for floor heating is 85F, and for
wall or ceiling panels, 120F.
Floor installations are most common. The coils are
imbedded in concrete approximately 1 in. below the surface.
If this is a concrete slab on grade, it should be insulated un-
derneath. In ceiling and wall applications there should be
coils for each room to be heated. When installations are on
outside walls, they should be insulated very well between thecoils and outside surfaces to prevent extreme heat loss.
Radiant heating installed in the floor is very comfortable
with little temperature variation from room to room. FigureA29 illustrates a polybutylene pipe being installed in a floor.The pipe is tied to a wire mesh and propped on blocks to keep
it near the top of the concrete slab, and the concrete is poured
around it, covering it by approximately 1 in. There should be
no joints in this pipe in the floor. Polybutylene pipe is popu-
lar for this installation. Any joints necessary should be man-
ifolded outside the slab. Almost any type of flooring material
may be used over the slab. Common materials are tile, wood,
12 Refrigeration and Air Conditioning Technology
LIQUID-TO-LIQUIDHEAT EXCHANGER
SENSOR
SENSOR
SENSOR
3-WAY VALVE 1
3-WAY VALVE 2
RETURN
COLLECTOR
ANTIFREEZE
PURGECOIL
LIQUID-TO-AIRHEAT EXCHANGER
ROOMTHERMOSTAT
ROOM
COIL
CONTROLLER
FURNACE SUPPLY
STORAGE
PUMP PUMP
A B
C
PUMP
Figure A26 A closed liquid collection, water storage system with air distribution to the house.
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Unit A Alternative Heating (Stoves, Fireplace Inserts, Solar)
COLLECTOR ARRAYCONVECTION HEATDISTRIBUTION COIL
AUXILIARYBOILER
AUXILIARYBOILER
AUXILIARYFIN TUBES
SOLAR FIN TUBES
2-POSITION, 3-WAYAUTOMATICDIVERTING VALVE
GATE VALVEGATE VALVE
PUMP
PUMPVENT
RETURNTOSTORAGE
RETURN TOBOILER
RETURN TOBOILER
RETURN TOSTORAGE
3-WAYAUTOMATICDIVERTINGVALVE
SUPPLYFROM
STORAGE
STORAGE TANK
(A)
(B)
STRAINER
Figure A27 (A) A liquid-to-liquid solar space-heating system. (B) Both solar and auxiliary heat can be used at the same time.
AUXILIARYBOILER
3-WAY AUTOMATICDIVERTING VALVE
3-WAY AUTOMATICDIVERTING VALVE
GATE VALVE
GATE VALVE
PUMPSTRAINER
SOLARSTORAGE
Figure A28 A solar space-heating radiant system. The radiant heating coils are normally embedded in a concrete floor.
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These collectors may use one or two panels of glass. This
glass may vary in quality and design, but a low-iron tem-
pered glass is often used. The absorber plate is usually made
of copper and formed tightly around the copper tubing and/or
may consist of fins welded to the tubing. These assemblies
are painted black, using a paint designed for this purpose, to
absorb the maximum heat from the sun.
A.17 SOLAR POOL HEATING
Many solar pool heating systems simply use the pump th
circulates the pool water through the filter for this system
The pool water is pumped through the filtering device(
and then is diverted to the solar collectors where it
heated. The water then flows back to the pool, Figure A3
This continuous flow of water through the collectors anback to the pool gradually heats the water. When the po
has reached the desired temperature level, the water b
passes the collectors and is returned directly to the po
from the filters.
Collectors for pool systems are often made of extrud
plastic, Figure A35. A cross section of a collector producby one manufacturer is shown in Figure A36. As shown bthis illustration, the collector receives diffuse radiation an
direct radiation for optimum heating of the water passin
through.
Unit A Alternative Heating (Stoves, Fireplace Inserts, Solar)
Figure A31 The heat exchanger piping has a double wall when an antifreeze solution is used in the collectors in a domestic hot water system
COLD WATER SUPPLYTO COLLECTORCIRCULATION PUMP
HOT WATER RETURNFROM COLLECTOR
TEMPERATUREMODULATING VALVE
TEMPERATURE-PRESSURE RELIEF VALVE
HOT WATER SUPPLY
CONVENTIONAL DOMESTICHOT WATER TANK
HOT WATER TRANSFERLINE TO WATER HEATER
COLD WATER SUPPLY FORTEMPERING HOT WATER SUPPLY
COLD WATER MAKE-UP
SOLARPREHEAT
TANK
Figure A32 A solar preheat tank provides additional storage for a domestic hot water system.
Figure A33 A solar collector. Courtesy AET
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SUMMARY
Approximately 20% more heat is available in dry wood than
in green wood.
Wood smoke contains both polycyclic organic matter (POM)
and nonpolycyclic organic matter, which are considered to
be health hazards. EPA standards exist for both catalytic and noncatalytic
stoves.
Creosote, when hot, is a thick dark-brown liquid that forms
into a residue like tar when it cools and often turns into a
black, flaky substance inside the chimney or stovepipe.
Stoves heat by both radiation and convection.
Pellet stoves burn small, compressed pellets made from
waste-wood products or agricultural waste products.
Makeup air must be provided to replace air used in the com-
bustion process.
Gas stoves may be certified by ANSI as a decorative appli-
ance or as a room heater.
Gas stoves may be designed to use a B-vent or a direct-vent,
or they may be vent-free.
Fireplace inserts convert a fireplace into a more efficient heat
source.
Both wood-burning and gas-burning fireplace inserts are
available.
Liquid solar forced air space-heating systems may be the
drain-down or closed-collector piping system type.
Liquid solar space-heating systems may be combined with
many types of conventional heating systems.
Solar heating may be used to heat domestic hot water.
Swimming pools may be heated with solar heating systems.
16 Refrigeration and Air Conditioning Technology
Figure A35 The solar collector for a swimming pool solar heatingsystem. Courtesy Aquatherm Industries/Solar Industries
Figure A36 A cross-sectional view of a swimming pool solarcollector. Courtesy Aquatherm Industries/Solar Industries
THERMOMETER
(OPTIONAL)
INLET LINE
TO SOLAR
COLLECTOR
FLOW
METER
VALVE
CONTROL
LINE
SP SOLAR
COLLECTORS
THERMOMETER
(OPTIONAL)
ISOLATION CHECK VALVE
(OPTIONAL)
OUTLET TEE
HEATER BY-PASS
BALL VALVE
(OPTIONAL)
HEATER
(OPTIONAL) HEATED WATER
TO POOL
CHECK
VALVE
ISOLATION
BALL VALVE
(OPTIONAL)
POOL WATER
SENSOR
POOL
FILTER
120/240 V LINE
ELECTRONIC CONTROL
PUMP
COOL WATER
TO SOLAR
HEATER
VACUUM RELIEF VALVE
(OPTIONAL LOCATION)
VACUUM RELIEF VALVE
SOLAR SENSOR
END CAP
OUTLET LINE
Figure A34 A swimming pool solar heating system. Courtesy Aquatherm Industries/Solar Industries