If you are thinking about installing a woodstove, here is some good information from Michigan State University:
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. (Vis. T1) 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
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. (Vis. 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
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 **** on metal brackets approximately 4 inches
behind the stove.
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 ashes.
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. (Vis. 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. (Vis. 4)
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
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
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 electrical fire.
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 undiscovered.
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
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 warned.
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
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 bulletin E-1390, Wood Stove Installation and
"It's been said that a long straight row of firewood standing in the yard in springtime is like money in the bank.
It is indeed.
As it dries in the summer sunshine, you're collecting interest."