State University Extension
Home Maintenance And Repair - 01500596
The hazards of heating with a wood stove include fires started by heat
radiated or conducted by the stove, stove pipe or chimney to walls,
floors and other combustible materials; fires started by sparks and
glowing coals falling out of front loading stoves when opened, and
fires started by flames leaking out of faulty chimneys or burning or
glowing material coming out of the top of the chimney. A chimney flow
reversal is also possible, leading to either flames or smoke coming out
of the stove's air inlets.
Before installing, seek advice from your stove dealer, your local
building inspector or fire department. And check with your insurance
agent. The insurance company may have its own specifications for
installation and, since you are changing the method of heating your
home, your agent must be notified in order to maintain fire insurance
coverage on your home.
The National fire Protection Association (NFPA) has developed standards
for clearances from walls and ceilings that are the basis for many
local building codes.
All combustible materials, woodwork,
unprotected walls, furniture, firewood, etc., should be no closer than
36 inches to a wood stove. A stove pipe should not be closer than 18
inches to an unprotected ceiling. These distances are important because
wood that is, continually reheated will ignite at much lower
temperatures than fresh wood. A new wall will start to burn at between
500 and 700 degrees F. If this wall is continually heated over a period
of time the wood will dry and eventually may start to char because of
radiant heat. The ignition temperature can drop to 200 to 250 degrees
F. For this reason an improper wood stove installation becomes a
potential time bomb.(Vis.
1) shows proper installation.
A simple test will tell if you have enough clearance to an unprotected
wall. Place your hand on the closest surface. If you can keep your hand
there comfortably while the stove is operating, the location passes the
test. If not, you need additional protection.
Spacing asbestos millboard or 28 gauge steel 1-inch away from the wall
allows you to reduce the distance a stove can be placed from the wall.
2) These materials absorb heat radiated from the stove and the
spacing lets air circulate behind the panel and cool the area between
the wall and the panel. The spacers should be made of non-combustible
material. A 1- to 1 1/2-inch gap between the panel and floor and at the
top of the panel is necessary to provide proper air flow. Asbestos
millboard is different from asbestos cement board or asbestos transite
board. Cement board or transite boards are both hard, slate-like panel
materials designed as a name barrier. They provide little in terms of
heat resistance and will conduct heat to any combustible surface to
which they are attached. Asbestos millboard is a soft, lightweight
panel product that can be easily cut with a saw or utility knife.
WARNING: Inhaling asbestos fibers may be harmful. The effect of long
term exposure is not completely known. However, you should wear a
protective mask when cutting asbestos products.
Since brick and stone are good conductors of heat, they offer little
protection if placed against a combustible wall or have wood studs
behind them. To be effective, bricks must be placed out at least 1-inch
from the wall with air gaps at the top and bottom. You can provide
these air gaps by using half bricks on the top and bottom row. Stoves
can be placed as close as 12 inches from the brick facing if you
provide an air space behind the brick.
An inexpensive and temporary way to protect a wall if you already have
a stove installed closer than 36 inches to an unprotected wall is to
provide a baffle. This baffle could be sheet metal, hardware cloth or
cement board hung on metal brackets approximately 4 inches behind the
All floors on which stoves are installed, except concrete, must be
protected from both heat of the fire and hot coals falling out when
fuel is added. Metal with asbestos backing and asbestos millboard are
non- combustible materials used for floor protection. Fireproof clay
tile, slate, brick, colored pebbles and marble chips can be used alone
only if they are mortared in place with no gaps. If they are not
mortared or have gaps, then metal or asbestos millboard must be
installed between them and a wood floor. A 2-inch layer of ashes or
sand or bricks laid in the bottom of the stove helps to insulate the
bottom of the stove and protect the floor. In general, 18 inches is
enough clearance to protect the floor if it is covered by non-flammable
material, such as a sheet of 24 gauge metal or brick or fireproof clay
tile. If the stove legs are from 6 to 18 inches long, 24 gauge sheet
metal laid over a 1/4-inch sheet of asbestos millboard is needed. Legs
of 6 inches or less require 2 to 4 inches of hollow masonry laid to
provide air circulation and covered by 24 gauge sheet metal. If the
stove has no legs, provide a sturdy support to allow air circulation
under the stove.
The floor protection should extend at least 12 inches beyond the sides
and rear of the stove, and at least 18 inches beyond the stove front,
to protect against falling embers and for loading wood or removing
Before installing heavy protection materials such as brick, check the
floor to make sure it can handle the increased weight. You may want to
reinforce the joists under the floor. Consult a carpenter if necessary.
The stove pipe or chimney connector runs from the stove to the chimney.
Many fires associated with wood stoves are caused by unsafe stove pipe
installation. A safe installation requires proper material,
construction clearances and does provide proper draft. A 24 gauge or
thicker metal is recommended; lower gauge numbers indicate thicker
metal. This gauge will provide better protection in the event of a
chimney fire and will also resist chemical corrosion longer. Most
stoves use either a 6 or 8-inch stove pipe. Using stove pipe that is
smaller in diameter than the fire box outlet will reduce combustion
efficiency and may cause improper draft.
Keep the connector pipe as short as possible. lt should not be longer
than 75% of the vertical chimney height above the flue inlet (where the
connector pipe enters the chimney). The maximum length is 10 feet. If
the pipe runs horizontally, it should have a rise of at least 1/4-inch
per linear foot from the elbow or stove outlet to the chimney inlet.
Use 45" angles to create an upward slope in the flue connector pipe.
Try to have no more than one right angle turn between the stove and
chimney. Additional right angle bends can cause soot and creosote to
collect in the smoke pipe or chimney, blocking flue gas flow and
increasing the danger of a fire.
The connector pipe diameter should be as large as the flue collar
(where the connector pipe joins the stove). When joining sections of
the pipe, overlap the joints at least 2 inches, with the crimped (male)
end pointing down to prevent creosote drip or leak. Many house fires
have resulted from stove pipe joints vibrating apart during a chimney
fire. Secure each joint with at least 3 sheet metal screws. A fireproof
sealant may be used in addition.
Clearances from a connector pipe must be 3 times the pipe diameter (a
6-inch pipe needs 18 inches clearance) unless the wall is protected.
3) You should not pass a stove pipe through a combustible wall but
if a stove pipe must pass through an interior combustible wall in order
to hook up with a chimney flue, there are 4 ways to do this safely.
1) Use an U.L. "All Fuel" thimble extending through the wall, with a
wall hole 4 inches larger than the thimble diameter. This permits the
placement of an insulating material such as fiberglass or rock wool
between the thimble and the wooden framing of the wall.
2) Use a ventilated thimble that is as least 3 times larger than the
stove pipe. For a 6-inch stove pipe, use a thimble that is 18 inches in
diameter. This type of thimble is not readily available but can be
fabricated by a sheet metal shop. Ventilation through this thimble is
an essential aspect of its design; the ventilating holes on either side
must not be blocked.
3) Use a fire clay thimble surrounded by 8 inches of brick work or
non-combustible material such as rock wool insulation.
4) Use no thimble but remove all combustible materials within 18 inches
on all sides of the stove pipe. Material for closing this opening must
be non-combustible, with insulating properties.
When the wall is cut between supporting studs for the thimble, inspect
the opening to make sure there are no electrical wires or conduit in
the space between adjoining wall studs. Heat from the stove pipe may be
sufficient to melt the insulation on wire in this space, causing an
Stove pipe should not pass through ceilings, closets, or outside a
building. Holes in the ceiling (including hot air registers) permit
fires through upper floors. A closet fire could smolder and spread
Running a stove pipe out a window and up the outside wall of the house
is a dangerous practice, because the pipe cools faster than a
prefabricated metal chimney and allows a rapid creosote buildup. Wood
burners sometimes recommend long spans of single thickness stove pipe
as a heating device. This idea had some merit when used with old
fashioned inefficient stoves where much of the heat went up the pipe.
Today's airtight stoves are more efficient and this practice may cause
rapid creosote buildup.
Some stove installations require a damper either built into the stove
or in the pipe near the stove to control draft and loss of volatile
gases. Check the recommendation of the stove manufacturer.
When connecting the stove pipe to the chimney make sure the fitting is
snug at the flue inlet. Use the proper thimble. The pipe must not
project into the flue itself, since it would hamper draft.
Long stove pipes and those with restrictions should be cleaned
frequently to prevent creosote buildup and possible chimney fires. The
entire length of the stove pipe must be easily inspected, firmly
fastened at the joints and kept free of all combustible materials. Tap
your pipe to check its condition several times during the heating
season and before starting the stove each year.
1. Chimney and chimney connectors require regular inspection and
cleaning to remain reasonably safe. Chimney fires are a common problem.
There are several factors that can cause a chimney fire.
2. Furniture, wood, newspapers, matches, etc., can ignite if placed or
left too close to a stove. These materials must be kept at least 36
inches away from the stove.
3. Stove surfaces can become as hot as 800 degrees F. At this
temperature, combustible material can ignite and plastic material will
melt. Be careful when drying clothing, making sure that nothing is
dangling too near. Also, remove any slipping or tripping hazards near
the stove to reduce the risk of falling against it and perhaps
suffering a severe burn. Small children must be taught to stay away
from the stove. You should erect some kind of barricade around the
stove if you have crawling tots who are too young to be verbally
4. Never use kerosene or charcoal lighter fluids to start a fire. Also,
do not burn trash in your stove. These materials lead to hot
uncontrollable fires and may cause a chimney fire.
5. Keep the fire controlled with the dampers. Do not let it get roaring
hot. A fire properly controlled is safer and more efficient.
6. If you want to keep your fire alive all night or when you are away
from the house, bank the fire with ashes or damper it way down. Do not
retire or leave home with a roaring fire going in the stove.
7. Place ashes in a lidded metal container. Because they might be hot,
clean up any ashes or cinders that spill out on the floor.
8. Wear gloves when handling rough or splintery chunks of wood. If they
are heavy, take care not to strain yourself or drop them on your foot.
9. You can burn wood in a coal stove, but you shouldn't burn coal in a
wood stove unless it is lined and designed for it. When you add coal to
an approved stove, keep the stove pipe damper open until the fuel is
burning well to avoid a potentially explosive buildup of gases from the
coal. Heavily laden coal buckets can also cause strains and other
mishaps if they are not handled properly.
10. Take down the stove pipe at least once or twice during the heating
season and clean out the soot. Removing the accumulated soot saves
fuel, increases heat and minimizes the danger of fire.
11. If you have yet to equip your house with fire warning devices, be
sure to do so when you install a stove. Install a smoke detector in an
adjacent room to avoid false alarms when you recharge the stove or from
backpuffing due to wind.
12. Before opening the fire box to add fuel or just to look at the
fire, always open the stove pipe damper first. This allows gases to
escape up the chimney and eliminates the possibility of "flare up" when
air suddenly comes in through the door.
13. With today's tightly-constructed houses, there may not be
sufficient air leakage for efficient stove operation. By providing an
outside air inlet, you prevent the possibility of a reverse draft which
may suck carbon monoxide fumes from combustion-type (natural gas, etc.)
appliances and discharge them into the living area.
This information comes from Michigan State University Extension
E-1390, Wood Stove Installation and Safety.
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This information is for
educational purposes only. References to commercial products or trade
names does not imply endorsement by MSU Extension or bias against those
not mentioned. This information becomes public property upon
publication and may be printed verbatim with credit to MSU Extension.
Reprinting cannot be used to endorse or advertise a commercial product
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employer. Michigan State University Extension programs and materials
are open to all without regard to race, color, national origin, gender,
gender identity, religion, age, height, weight, disability, political
beliefs, sexual orientation, marital status, family status or veteran
status. Issued in furtherance of MSU Extension work, acts of May 8 and
June 30, 1914, in cooperation with the U.S. Department of Agriculture.
Thomas G. Coon, Director, MSU Extension, East Lansing,MI 48824. This
information is for educational purposes only. Reference to commercial
products or trade names does not imply endorsement by MSU Extension or
bias against those not mentioned.
information.was reviewed as
of June 2008. For more information about the contents please
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