Newmac WG-100 Service manual

INSTALLATION, OPERATING
and
SERVICE MANUAL
WOOD-COAL FURNACE WG-100
WOOD-COAL-ELECTRIC WG-100E
WOOD FURNACE WB-100
WOOD-ELECTRIC FURNACE WB-100E
All installations must be made in accordance with local and
provincial or state codes which may differ from the manual.
HEAD OFFICE
MARKETING / PRODUCTION
Newmac Mfg. Inc.
208 LANCASTER CRESCENT
P.O. BOX 9, DEBERT
NOVA SCOTIA, BOM 1G0
PHONE: [phone]
FAX: [phone]
WAREHOUSE
Newmac Mfg. Inc.
430 SPRINGBANK AVE., SOUTH
WOODSTOCK, ONTARIO
N4V 1B2
PHONE: [phone]
FAX: [phone]
EMAIL: [e-mail] HOMEPAGE: newmacfurnaces.com
NOTICE TO HOMEOWNER:
READ THESE INSTRUCTIONS
SAVE THESE INSTRUCTIONS
2210058 Revised February 2010
Printed: _______________
Subject to change without notice

1
SOLID FUEL FURNACE MODELS WB-100, WG-100
General Instructions
It is the responsibility of the consignee of the furnace to examine the package for damage and, if found, to note the
same on the Carrier’s Bill of Lading.
Model WB-100 – furnace with brick liner.
Model WG-100 – furnace with brick liner and cast iron grates.
The Model WB-100 and WG-100 has the furnace in one package and the firebrick in another package.
Package Contents:
#1 Heat exchanger with all panels installed, blower with motor, belt and pulleys installed, filters installed, draft fan
c/w thermostat, and instruction booklet in blower compartment. Brick rack and 2 brick in firebox of WB-100 model.
Brick rack and 6 split brick in firebox of WG-100.
#2 WB-100 – 3 Boxes of 8 Full Firebrick (24 bricks)
WG-100 – 2 Boxes of 10 Full Firebrick (20 bricks)
Installation
*Check with provincial, state or local codes concerning clearances, chimney requirements and other installation
procedures before installation. Some codes may vary from the requirements set forth in this manual.
Minimum Installation Clearance From Combustible Material
FROM MINIMUM CLEARANCE
Fire door end 48”
One Side 6”
Other Side (Walkway) 24”
Blower door end 30”
Flue Pipe 18”
Plenum and Takeoff Ducts to 6’ from Furnace 6”
Duct beyond 6' from Furnace 1/2”
WB & WG models return air plenum and take off ducts to
6’ from furnace 6”
Floor non-combustible
Solid fuel or other combustibles must not be stored within the above clearances.
1. Model WB-100 – Install brick in firebox according to Diagram #1. After brick is in position place 2” of sand in
bottom of firebox. (Use pit sand only.) Install draft fan & thermostat according to Wiring Diagram #3 or #4.
2. Model WG-100 – Install brick according to Diagram #2. Install draft fan and thermostat according to Wiring
Diagram #4.
3. Do not use a flue damper with this furnace.
4. Caution: If this furnace is used as a replacement for an existing furnace observe the following:
a. Make sure there is a minimum of 6” clearance above the warm air plenum as far as 6 feet out from the
furnace. Beyond 6 feet there must be a minimum of 1/2” clearance.
b. Metal return air ducts must be used. (No combustible materials in return air ducts.)
c. Use flue pipe as per B365 Clause 5.

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This furnace must be connected to a chimney approved for wood burning appliances, ie. ULC S629 (Canada) and
UL103 (US), or a masonry chimney conforming to the requirements of provincial regulations or, in the absence of such
regulations, to the requirements of the National Building Code of Canada. Newmac recommends an 8” round or 8”
square chimney flue (inside dimension), however, this may be reduced to a 7” providing there is enough draft at the
appliance to operate as designed. It is the responsibility of the installer to ensure there is sufficient draft in all cases.
Draft should be between -0.03 and -0.05 ins wc. No other appliance should be connected to this chimney flue, unless
the installation conforms to clause 5 of B365.
amended May 2009
The installation must conform with the regulations of the local authorities having jurisdiction with the applicable
Electrical Code, and with the regulations in C.S.A. Standard B365 “The Installation Code for Solid Fuel Burning
Appliances and Equipment”.
Flue pipe connections must be secured with metal screws and have as few elbows as possible. Fuel storage should
conform to local bylaws. This furnace should be installed by a qualified furnace serviceman.
Caution:
The flue collar is sized so that a trade size flue pipe fits snugly inside it. Joints in flue pipes, including the connection
at the appliance and the chimney, shall have at least 30 mm (1 3/16 inch) over lap. Flue pipe connections must be
secured with at least 3 metal screws or an equivalent mechanical means; and be made tight in accordance with
good practice.
The flue products may contain carbon monoxide particularly when the wood fire is being starved for air (made to
burn at slow rate). Therefore, the flue pipe must seal tight and must not be inserted into the return air stream of the
circulating blower.
Wood storage should conform to local bylaws, and should not be within minimum clearances for combustible
surfaces as shown above. This furnace must be installed by a qualified furnace serviceman.
NOTE:COMBUSTION AIR: Where fans are used in the fuel storage area, they should be installed so as not to create
negative pressures in the room where the solid fuel burning appliance is located.
OUTSIDE COMBUSTION AIR: Provision for outside combustion air may be necessary to ensure that fuel-burning
appliances do not discharge products of combustion into the house. Guidelines to determine the need for additional
combustion air or not may not be adequate for every situation. If in doubt, it is advisable to provide additional air.
Outside combustion air may be required if:
1. the solid-fuel-fired appliance does not draw steadily, experiences smoke roll-out, burns poorly, or back-drafts
whether or not there is combustion present.
2. existing fuel-fired equipment in the house, such as fireplaces or other heating appliances, smell, do not operate
properly, suffer smoke roll-out when operated, or back-draft whether or not there is combustion present;
3. any of the above symptoms are alleviated by opening a window slightly on a calm (windless) day;
4. the house is equipped with a well-sealed vapor barrier and tight fitting windows and/or has any powered devices
which exhaust house air;
5. there is excessive condensation on windows in the winter; or
6. a ventilation system is installed in the house.
If these or other indications that infiltration air is inadequate, additional combustion air should be provided from the
outdoors.
DUCT INSTALLATION: Not to be connected to ductwork that is still connected to another furnace.
Because the unit may be used as a gravity furnace when the power is off, the following is recommended:
1. Locate the furnace as centrally as possible in the home so the best warm air distribution may be enjoyed.
2. Use an extended plenum (central duct) at least one size larger than called for in National Warm Air Standards.
3. Use a minimum pipe size of six inches diameter in runs and in no case smaller than five inches diameter.
4. Slope extended plenums and runs as much as possible to facilitate gravity flow of warm air.
BELT TENSION: When adjusting the proper pulley setting make certain that the belt is able to flex approximately
one inch without movement of the motor pulley.
IMPORTANT: This furnace must have a MINIMUM return air duct size equal to 250 sq. in. and a MINIMUM supply
air duct size equal to 180 sq. in. The supply air extended plenum should extend 8 – 10 feet out from the furnace,
then gradually transitioned to the end of the duct system to provide a .20” W.C. static pressure.
HUMIDIFIER
Install the humidifier in the return air plenum. This prevents possible damage due to excessive temperatures when
there is a power failure.
Metal connecting ducting from the warm air plenum is recommended rather than plastic ducting.

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BURNING WOOD OPERATING INSTRUCTIONS
When installation is complete, close the supply switch and turn the thermostat above room temperature.
Check to make sure the forced draft fan above the fire door is operating when the thermostat is set above
room temperature.
The draft fan should be off when thermostat is set below room temperature.
The maximum draft is not to be more than - .05 as damage may result to the furnace when operated as a
gravity unit.
The circulating air blower speed is adjusted at the factory to give an adequate temperature rise under most
conditions. However, because of various temperatures that can result from burning wood, the blower speed
can be adjusted by the motor pulley. Under no circumstances should the temperature rise be more than
80oF (27oF).
NOTE:Before loading the fire box, turn the thermostat up to insure that the draft fan is on. This provides an air
curtain to avoid smoke roll out during loading and fans the coals to assist the ignition process of your new
fuel. It also helps to promote draft when there is inadequate draft. After the fire is established, set the
thermostat to desired temperature.
To start the fire, turn up the thermostat to Maximum setting to turn ON Forced Draft Fan. Place some
newspaper crumpled up in the bottom of the firebox on top of the minimum requirement of 2” of sand , ash
or firebrick. Add some small kindling and light the fire. When the fire starts add some larger pieces of
kindling or wood until you have a good fire. The idea is to ultimately end up with a good bed of ash and
coals which helps to maintain a good controllable fire.
When reloading the firebox there will be a build up of ash and coals from the previous fire. Rake the coals
mixed with ash to the front of the firebox which places the coals at the front. Throw in your wood and the
fire should light in a few minutes.
When the firebox gets full of ash (within one inch of door level), some morning , before loading the firebox ,
push or rake the coals to the rear of the firebox. Remove the ash from the front of the firebox using only the
shovel supplied for this purpose. When the ashes only are removed from the front , rake the coals from the
back to the front. Throw in your wood and the fire will again be burning in a few minutes. The fire burns
best when the ashes are 3” to 4” below the fire door level.
Return wood thermostat in main living space to regular setting.
For safe operating procedure, refer to the “Notice” label on the furnace.
COMBUSTION AIR CONTROL
The amount of combustion air allowed to enter into the firebox can be controlled by means of the Draft
Control slide on the draft fan mounting plate. Set this slide plate to the position that allows sufficient
combustion air in for the type of solid fuel being burned. Normally the setting is in the center between
maximum and minimum, then if additional control is needed it can be adjusted accordingly. When burning
coal it must be set at maximum, for burning wood it will vary with size and type. DO NOT LET THE
COALS/ASHES BUILD UP ANY HIGHER THAN HALF WAY UP THE FIRE BOX LINER.
POWER FAILURE
In case of prolonged power failure, remove the blower access door and air filters. The draft fan will be off,
so if more combustion air is needed for the wood fire, open the slide plate damper in the fire door. This
damper must be closed when power is returned to normal.
DO NOT CHARGE the fire box higher than half way up the liner as overheating may result.
COAL BURNING TIPS (Furnace Model WG 100)
Burn ONLY anthracite (hard) coal of the “chestnut” size. Bituminous (soft) coal is not recommended
because it has a high ash and sulfur content which means more cleaning and greater pollution. Also
bituminous coal produces excessive smoke and an excessive amount of dirt and ash which will plug the
heating unit and the flue pipe possibly causing smoke damage or danger of carbon monoxide poisoning.
Coal is not as easy to burn as wood. It requires patience and a very specific and regular procedure of
loading, shaking, adjusting, etc. If you do not follow the correct procedure, the coal fire will go out. This
can happen in a very short space of time and once the process of extinction has started, it is almost
impossible to reverse.
After a coal fire goes out, all the coal must be emptied from the furnace and the complete starting
procedure must be repeated. The coal burning learning process is often long and frustrating, but once the

4
proper procedure is established and followed, coal burning becomes a reasonably simple process with the
benefits of long burn times and evenness of output over the entire length of burn.
STARTING UP A NEW FIRE
The flue draft must be -0.05” W.C. to allow combustion gases to flow freely out the chimney. Turn the solid
fuel thermostat up to a setting well above the room temperature to start the draft fan. Use paper and dry
kindling to start the fire.
Add small compact pieces of hardwood when the kindling is burning hot. Keep the draft fan slide plate in
the ash door fully open to establish a hot fire. The ash door may be opened for start up. However, close
the ash door before opening the fire door to prevent smoke from emitting out the fire door opening.
When a substantial bed of red coals is built up, start adding coal, small amounts at a time. Continue adding
small amounts of coal until there is a solid bed of burning coal. Do not add too much at one time. Allow
sufficient time between each small loading (at least 10 to 15 minutes) so that each loading has time to
thoroughly ignite before the next load is put in. For maximum burning efficiency, always fill the furnace to
the highest level possible. A deep bed of coal always will burn more satisfactorily than a shallow bed.
Keep the draft fan running until you are sure the fire is continuing to burn hot, then turn the thermostat to
the desired room temperature setting. If the ash door has been opened, close it to prevent overfiring, which
can severely damage the furnace.
LOADING
Coal should be added to the fire at least every twelve hours. Coal never should be added unless there is a
reasonably hot fire.
If the fire is burning hot and there is a deep bed of coals, full loads of coal can be added at any time.
However, if there is not a deep bed of coals, it is best to add small amounts of coal at first.
SHAKING
Shaking should be done only with a hot fire. Shaking should be done at least once a day, but not more
than twice a day. Best results from shaking will occur if short “choppy” strokes are used rather than long
even strokes. The amount of shaking is critical. Too little or too much can extinguish a fire due to blocked
airflow. The proper amount normally occurs when red coals first start to drop through onto the bed of
ashes. Be sure that a small amount of ash is left on the grates to protect them from the direct heat of the
burning coal.
MAINTENANCE
Ashes never should be allowed to accumulate in the ash pit so they in any way impede the flow of
combustion air to the fire. Excess ash accumulation can cause the fire to go out, and also can cause
severe damage to the grates because they cannot cool from a flow of air beneath them. Ashes MUST be
removed daily and put in a metal container with a lid.
Clinkers can occur in any coal furnace. They are pieces of fused ash that are hard. They can become
large, and therefore cannot be shaken through the grates in a coal furnace. When there is an appreciable
accumulation, the fire will go out because insufficient air is allowed to pass through the clinkers to the
burning coal. Once clinkers have formed, they can be removed only from above the grates. This usually
means the fire must be allowed to die out before they can be removed.
Clinker formation can occur from a number of different causes or a combination of causes. Some of these
are as follows:
 Too hot a fire (too much draft)
 Too shallow a bed of coals
 Too deep a bed of coals
 Excess shaking
 Poking the fire from the top
 Poor quality coal – excess ash content
 Too little air (draft) after a long hot fire

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SAFETY
Whenever a loading door is opened, it always should be cracked slightly before fully opening to allow
oxygen to enter and burn any combustible gases that are present. Failure to do this could result in sudden
ignition of the unburned gases when the door is opened.
A furnace never should be filled with excess coal so that the flue gas exit is in anyway blocked or impeded.
Burning coal generates carbon monoxide. If the flue gas exit is blocked, the carbon monoxide can be forced
out of the furnace into the room, with possible fatal consequences. Never burn coal in any furnace that
does not have an airtight, unified chimney system. The furnace should be used only with chimney systems
that provide a strong, reliable draft. With the exception of the start-up period, an ashpit door NEVER should
be left open.
Do not use an automatic stoker with this furnace.
NOTE: Grates must be maintained in a level position or they will warp.
MAINTENANCE
Failure to follow these instructions may result in poor efficiency, excessive corrosion of the heat exchanger
and the possibility of a creosote fire.
DAILY: Furnace models with grates must have the ashes removed daily. This is to prevent warping of the
grates and prevent any interruption in the combustion airflow. Ashes must be put in a metal container with a
lid on it before moving the ashes to the outdoors.
MONTHLY: Furnace heat exchanger and flue pipe – Furnaces without grates must have ashes removed
on a minimum of a monthly basis depending on the ash build up. The complete heat exchanger and flue
pipe should be thoroughly inspected for creosote deposits, ash buildup, etc. Creosote or ash deposits must
be removed by scraping and/or brushing the deposits from the heat exchanger surfaces. An industrial
vacuum cleaner may be used to assist in the removal of such deposits. A complete cleaning must be done
immediately at the end of each heating season. If this is not done, condensation from the summer months,
or any other source, will mix with the ash or creosote and cause corrosion of the heat exchanger. Corrosion
is not covered under warranty.
NOTE: Establish a routine for the storage of fuel, care of the appliance, and firing techniques. Check daily
for creosote buildup until experience shows how often cleaning is necessary. Be aware that the hotter the
fire, the less creosote is deposited and weekly cleaning may be necessary in mild weather even though
monthly cleaning may be enough in the coldest months. Have a clearly understood plan to handle a
chimney fire.
CHIMNEY: Chemical chimney cleaners are not recommended as they could damage the furnace heat
exchanger and flue pipe. One of the most efficient methods to clean a chimney is to lower a stiff brush
(chimney brush) tied to a heavy weight down the chimney on a rope. Work the brush up and down the
chimney to scrape the accumulated creosote and soot off the chimney walls. Remove the residue from the
cleanout at the base of the chimney.
SEMI-ANNUALLY: Draft Fan – oil motor with #20 non-detergent oil.
ANNUALLY: Burner Motor and Blower Motor – oil with #20 non-detergent oil. In the spring, after the
furnace is shut down for the summer, clean the heat exchanger of all soot, ash and creosote accumulation,
remove all ashes, clean the flue pipe and clean the chimney. KEEP THE FIREDOOR OPEN
APPROXIMATELY 2” TO INSURE MOISTURE REMOVAL DURING SUMMER.

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NOTICE
IMPORTANT:
 This furnace must be installed according to CSA Standard B365 “Installation Code for Solid-Fuel
Burning Appliances and Equipment”.
 The solid fuel side of this furnace is designed to burn wood only, unless equipped with grates thus
allowing the burning of coal. Burn anthracite coal only.
 Proper flue draft must be maintained to allow combustion gases to flow freely out the chimney.
FOR SAFE OPERATION:
 Load fuel carefully or damage may result.
 Do not load solid fuel higher than the fire box liner.
 Do not use chemical or fluid fire starters.
 Do not attempt to light a fire when there is oil vapour present.
 Minimum flue draft - .03” W.C.
 Maximum flue draft - .05” W.C.
 Do not burn garbage, manufactured fire logs, gasoline, naptha or crankcase oil.
 Keep the furnace doors tightly closed except for refueling and cleaning.
 To maintain furnace efficiency and prevent soot fires, clean the heat exchanger, flue pipes, and
chimney at the end of each heating season and as frequently as required during the heating season to
prevent soot accumulation. The furnace and flue must be in good condition. Turn off power to the
furnace when cleaning the furnace and flue.
 Do not store fuel or combustible material within the furnace clearances.
 Do not use salt wood (driftwood gathered from the seashore).
TO PREVENT DAMAGE:
 Do not set the flue draft above - .05” W.C.
 Do not open the furnace door slide plate damper during normal operation.
 Furnaces with grates must have ashes removed daily.
 Furnaces without grates require a minimum of 2” of sand or wood ash in bottom of firebox.
SPECIAL PROCEDURES
POWER FAILURE:
1. Remove the blower access door and air filters for better air circulation. If the furnace is in an enclosed
area (furnace room) open the door to the room.
2. To control the fire, open the slide plate damper in the furnace door. THIS DAMPER SHOULD BE
CLOSED FOR NORMAL OPERATION.
3. Do not load the firebox higher than half way up the fire box liner.
SOOT FIRE
Close all sources of air that can reach the fire through the furnace and draft regulator. Insure the draft fan
above the fire door is turned off. Do not attempt to take the flue pipes down until the fire has been
completely extinguished.
RUNAWAY FIRE
This can be caused by too high a flue draft or excessive fueling.
1. Close all sources of air to the furnace. Insure draft fan is turned off.
2. Set the barometric draft regulator wide open to reduce draft. The excessive heat caused by a runaway
fire may damage the furnace safety controls. Their operation should be checked before the furnace is
returned to service. After a soot or runaway fire inspect chimney connection and chimney.
MINIMUM INSTALLATION CLEARANCES FROM COMBUSTIBLE MATERIAL
Fire door end – 48”
One side – 6”
Other side (walkway) – 24”
Blower door end – 30”
Flue Pipe – 18”
Plenum and takeoff ducts to 6’ from furnace – 6”
Duct beyond 6’ from furnace – 1/2”
Floor non-combustible

7
Diagram #1 - WB100 Firebox Installation Procedure
INSTALLING BRICK
1. Place brick lock in furnace brick lock hooks
2. With brick lock in place, raise rear of brick
lock by placing two (2) bricks on end to
support rear of brick lock (WG100). For
WB100 place two (2) brick on end and one
(1) brick on side. Rear now should be 4”
higher than front of brick lock.
3. Install brick by starting at front and working
back.
4. Lower brick lock into place.
Diagram #2 – WG100 Firebox Installation
GRATES:
Shipping retainer should be removed to allow
grates to turn and shake freely.
TO REMOVE A GRATE:
1. Remove front casting.
2. Slide grate as far forward as possible.
3. Lift rear end of grate approximately 6 inches.
4. Slide grate back toward rear of firebox and
up.
TO INSTALL A GRATE:
1. With rear end of grate higher than front end,
slide grate forward so shaft is through grate
retaining hole at front of firebox
2. Lower rear end of grate and slide rear shaft
of grate into rear retaining hole
3. Replace front casting if coal is to be burned.
FRONT CASTING:
Use for coal burning only.
Installation:
1. Remove top brick lock.
2. Put casting through firedoor and hold tight to
inside front of firebox above the brick.
Square pattern on casting should be facing
into the firebox.
3. Lower casting so it rests on round shaft of
grates.
4. Replace top brIck lock.
NOTE: This front casting is not required when
burning wood. However, this casting or provided
grate plate should be placed on top of the grates
for more efficient wood burning and to prevent
wood coals from falling through and warping
grates.
Diagram #2A – GRATE PLATE
NOTE: WB100 & WG100 Single Tube Only – Place baffle on top of side angles, allowing holes in baffle to
drop over pins. (Baffle may be turned over should warpage occur).

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Diagram #7 – Combustion Air Flow
Combustion Air Flow
Model WB100 Combustion Air Flow Model WG100

9
Diagram #3 - Newmac WB100, WB100E Furnace Wiring
(when equipped with R8222A Relay or equivalent)
Diagram #4 -Newmac WG100, WG100E Furnace Wiring
(when equipped with R8285 Switching Relay Transformer, also for WB100)

10
Diagram #5 - Newmac WB100 Furnace Control Locations
Fan Control Set Points: FAN ON: 140
FAN OFF: 100
Diagram #6 - Newmac WG100 Furnace Control Locations
Fan Control Set Points: FAN ON: 140
FAN OFF: 100

11

12

13

14

15
WB100/WB100E PHYSICAL WIRE LOCATION

16
WG100/WG100E Physical Wire Location

17
PREPARATION OF WOOD
Once I have my wood at home, how do I prepare it for burning?
The wood must be cut to length to suit the firebox of the stove, furnace, or fireplace in which it is to be
burned. An 8’ log may be cut into four, six or eight pieces, depending on the desired length. Splitting the
wood greatly facilitates drying and reduces the wood to a more manageable size.
How much moisture is contained in wood?
Many softwoods have a moisture content in the vicinity of 55 percent when they are freshly cut. The
popular hardwoods have moisture contents of about 45 percent. Air dried wood has a moisture content of
about 15 percent and kiln dried wood may have a moisture content of less than 10 percent when it is fresh
from the kiln.
What causes wood to rot?
When wood is cut, it is very susceptible to the growth of fungi, which converts the wood to water, carbon
dioxide, and heat, just as does a fire. This rotting decreases the wood’s energy. The fungi are most
productive when three conditions are met: the temperature is between 600F and 900F, the wood’s
moisture content is above 30 percent, and ample oxygen is available. Thus, wood does not rot appreciably
when it is dry, in the winter, or when it is submerged in the water, but it should not be allowed to lie on the
ground during the summer.
How can this rotting be prevented?
When the wood has been cut into stovewood lengths, and split, it should be piled outside during the months
of June, July, and August. Two poles should be placed on the ground to serve as rails to keep the firewood
off the moist ground and the wood should be piled up in such a way that it is well exposed to the sun and
the wind. The moisture content of the wood will drop until it reaches equilibrium with the ambient weather
conditions. When the relative humidity is 60 percent, the equilibrium moisture content is about 11 percent.
When the wood has reached this equilibrium moisture content, it is said to be “air dried.” Around mid
August, it should be placed under cover so that it will not reabsorb moisture from the rain and snow before it
is used.
Why this concern about allowing the wood to dry?
Green or wet wood is undesirable for several reasons. Green or wet wood tends to mildew and rot which
causes a significant reduction in the thermal value. When green or wet wood is burned, it may take 20 to
25 percent of the thermal value of the wood heat to evaporate and drive off the moisture, which is
contained. Green wood does not burn easily and, in order to keep the fire burning, it is often necessary to
add a lot of fuel and provide excessive draft, thereby decreasing the efficiency of the unit. The excess air
needed for combustion must be heated and it escapes up the chimney wasting heat that should be used to
heat the house.
What is creosote?
Wood smoke almost always contains some unburned gases and a fog of unburned tar-like liquids. Some of
these materials will condense on the inside of the chimney, just as steam condenses on any cold surface.
This condensation is a black, tacky, fluid when first formed. When it dries, it is flaky and shiny. Creosote
has approximately the same thermal value as fuel oil. Not only does it reduce the effective size of the
chimney, but an accumulation of this material constitutes a serious fire hazard.
Does green wood cause creosote?
Yes. Indirectly, green wood does cause creosote. The exhaust gases cool as they rise up the chimney. If
the temperature falls below the dew point, any moisture contained in these gases will condense on the
inside of the chimney, absorb the various products of incomplete combustion and form creosote. When
green wood is burned, the exhaust gases carry a high moisture content in addition, because of the heat
required for evaporation, these gases are cooler and more likely to condense than would be the case with
dry wood.
Charcoal may be formed more readily if the unit is overcharged, particularly in milder weather. With
overcharging (too much wood in unit) the draft fan will be off a greater percentage of time, coals will be
formed which will become covered with ash and in turn will smother the coals to form charcoal. Any coals
in the furnace should be stirred before more wood is added to it.

18
The preceding is an excerpt from a document prepared by the Nova Scotia Energy Council and the Nova
Scotia Research Foundation Corporation.
CREOSOTE AND CHIMNEY FIRES
Wood combustion is never perfectly complete. Wood smoke almost always contains some unburned
gases and a fog of unburned tar-like liquids. Some of these materials will condense out of the flue gases
onto any surface which is not too hot. The condensate is usually dark brown or black, and has an
unpleasant acrid odor. It is called creosote. If condensed on a relatively cool surface (such as an exterior
stovepipe chimney), the creosote will contain a large amount of water along with the organic compounds,
and will thus be very fluid. Water is usually absent if the condensation occurs on surfaces hotter than
1500F. The condensate may then be thick and sticky, like tacky paint or tar. Creosote may be found almost
anywhere in a wood-heating system, from the top of the chimney to the insides of the cover itself.
Creosote which remains in a chimney after its initial formation may later be significantly modified both in
physical form and chemical content. The water and the more volatile organic compounds tend to
evaporate, leaving the more tar-like substances behind. If these are subsequently heated by the flue gases
from a hotter fire (this usually happens), they themselves are further pyrolyzed to the same final solid
product that wood is carbon. The physical form is usually flaky, and often shiny on one side. Partially
pyrolyzed deposits can have a bubbly appearance. The flakes do not adhere strongly to a stove pipe and
thus are easy to brush off; some of the other forms will not budge even under the action of a stiff wire brush.
The amount of creosote deposited depends mostly on two factors – the density of the smoke and fumes
from the fire, and the temperature of the surface on which it is condensing. Highest smoke densities occur
when a large amount of wood in relatively small pieces is added to a hot bed of coals and the air inlet
damper is closed. Here, there is considerable pyrolysis of wood, but little combustion, and little air to dilute
the smoke. In practice, creosote generation is higher during low-power, overnight, smoldering burns.
Smoke densities are least when combustion is relatively complete, which tends to be the case when the
amount of excess air admitted to the wood-burner is high. Leaky stoves, open stoves and fireplaces
typically have the least creosote problems.
One way to lower the average smoke density in an airtight stove is to use less wood each time fuel is
added, and/or to use larger pieces of wood. In either case, the air supply need not be turned down so
much in order to limit the heat output and combustion is likely to be more complete. Of course, if less wood
is added, stokings must be more frequent. A related procedure to limit creosote is to leave the air inlet
moderately open after adding wood until the wood is mostly reduced to charcoal, and then close the inlet as
much as desired. This will promote complete combustion during pyrolysis, when the creosote compounds
are being formed, but there will be a significant heat surge while the gases are burning.
Extra air can also be added to the flue gases in the stove pipe; this is what the Ashley creosote inhibitor
does. But the net effect of adding dilution air is not obvious or necessarily beneficial. Dilution air will
decrease the smoke density, but it will also decrease its temperature. These effects have opposing
influences on creosote formation. The National Fire Prevention Association states that dilution air
increases chimney deposits. In any case, the cooling effect of dilution air does decrease the heat transfer
through the stovepipe and chimney, thus decreasing the system’s energy efficiency.
Creosote formation may also depend on the type of wood burned and on its moisture content. Dry
hardwoods have a reputation for generating the least creosote, but the quantity can still be very large. No
kind of wood eliminates creosote formation.
For a given smoke density near a surface, the cooler the surface, the more creosote will condense on it.
The phenomenon is very similar to water vapor condensing on the outside of a glass of ice water on a
humid day, except for an inversion – condensation occurs on the inside of a chimney, especially when cold
air outside makes the inner chimney surface relatively cool. A stovepipe chimney outside a house on a cold
day will be wet on the inside with creosote (including a lot of water) virtually all the time. A well insulated,
pre-fabricated metal chimney has the least serious creosote problems; its insulation helps maintain higher
temperatures on its inner surface, and its low heat capacity allows it to warm up very quickly after a fire is
started. Masonry chimneys frequently accumulate deposits at the beginnings of fires and their interior
surfaces take a longer time to warm because the construction is so massive. Any type of chimney which
runs up the outside of a house is more susceptible to creosote problems than the same type of chimney
rising in the houses’ interior, due to the cooling effect of the colder outdoor air on the exterior chimney.
Average flue gas temperatures can be increased by minimizing the length of stovepipe connecting the
stove to the chimney. This, of course, will also decrease the energy efficiency of the system, and it is often
true that measures which decrease creosote formation also decrease heating efficiency. For instance,
stoves which have energy efficiencies due to their relatively good heat transfer (e.g. the Sevca, lange 6303

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and double barrel stoves) are more likely to have chimney creosote problems precisely because they do
such a good job extracting heat from the flue gases.
Generally creosote is inevitable and must be lived with. Any kind of chimney deposit decreases the
system’s heating efficiency. Soot and dried creosote accumulations have a significant insulating effect;
less of the heat in the flue gases transferred into a house through dirty stovepipes and chimneys. The most
annoying problem can be creosote dripping from a stovepipe or chimney, and the most dangerous problem
is chimney fires, during which the creosote, or its pyrolyzed residue, burns.
Creosote dripping can usually be eliminated. Joints in vertical segments of stovepipe will not leak if, at the
joints, the smaller, crimped ends always stick down into the receiving end. (Smoke will not leak out of the
joints due to this direction of overlap.) Since this is not the usual orientation for stovepipe, a double male
fitting may be necessary at some point to connect the stovepipe to the stove, a prefabricated chimney, or a
rain cap. Special drip proof adapters are available for connecting some sizes of stovepipe to Metalbestos
brand prefabricated chimneys. Common types of stovepipe elbows can leak creosote due to their swivel
joints; rigid and accordion type leak proof elbows are available. Horizontal or gently sloping joints between
horizontal pipes and/or fittings are the most difficult to seal against dripping. A good high temperature
sealant can sometimes help, but is no guarantee. The joint must also be snug, and well secured with sheet
metal screws. If all joints are made leak proof, then the creosote will generally drip into the stove, where,
when the fire is hot, it will be burned.
Chimney fires occur when the combustible deposits on the inside of a chimney burn. The deposits may be
‘raw’ creosote, pyrolyzed creosote, or soot. Ignition requires adequate oxygen, which is usually available
and sufficiently high temperatures the same conditions as for the ignition and combustion of any fuel.
Chimney fires are most likely to occur during a very hot fire, as when cardboard or Christmas tree branches
are burned, or even when a stove burns normal wood, but at a higher than normal rate. A crackling sound
can often be heard at the beginning of a chimney fire. As the intensity of the fire rises, the stovepipe will
sometimes shake violently, air will be very forcefully drawn in through the stove, and the stovepipe may
glow red hot. A tall plume of flame and sparks can be seen rising from the top of uncapped chimneys.
The most effective way to suppress a chimney fire is to limit its air supply, although both water and salt are
sometimes suggested if a relatively airtight stove is the connected appliance. This is easily done by closing
the stove’s air-inlet dampers, if all the stovepipe and/or chimney joints are tight, and if no other appliance is
connected to the same flue.
In a properly designed and maintained chimney, the only potential hazard related to chimney fires is ignition
of the building’s roof or surroundings due to sparks and burning embers coming out of the top of the
chimney. A spark arresting screen can decrease, but not eliminate this possibility, but spark screens
themselves are often not suitable for use with wood fuel because they can become clogged. The chimney
itself and the stovepipe, when properly installed, are intended to withstand an occasional chimney fire
without danger of ignition of their surroundings. During a chimney fire, one ought to check the roof and
surroundings, and possibly wet down critical areas. If the chimney may not be up to safety standards, one
should also keep a close watch on all surfaces near the chimney.
Some people start chimney fires fairly frequently, as a means of chimney cleaning. This deters very intense
chimney fires and the small ones which do happen are always under a watchful eye. Under some
circumstances, this practice may be reasonable, but generally it is a risky method to keep a chimney clean.
There is always some danger of a house fire, but in addition, any chimney fire is wearing on a chimney; the
high temperatures increase the corrosion rate of metals and the thermal expansion of masonry materials
encourage crack formation and growth.
Chemical chimney cleaners are available. Opinions on their effectiveness vary, but apparently when used
regularly, and as directed, they work, and do not damage chimneys. The usual chimney cleaning method is
the oldest human energy and some kind of mechanical tool. A stiff wire brush, a heavy chain (perhaps in a
bag) hung with a rope and worked up and down from the top of the chimney, and very small brushes have
all been used. Professional chimney sweeps are also reappearing.
Some people clean yearly, other after every few cords of wood burned, but there are so many factors
influencing creosote build up that such generalizations are not appropriate in most particular cases. In new
installations, or when changes occur (such as a different stove) the chimney should be checked frequently
(after 2 weeks, then after a month, then after another 2 months, etc.) until it is clear how frequently cleaning
is usually needed.
The preceding is an excerpt from “THE WOODBURNERS ENCYLOPEDIA” published by Vermont
Crossroads Press, Inc. – Dec., 1976.