In a previous post we focused on wall and floor clearances for wood stove installation and materials that can be used to protect surfaces that where full clearance is not possible. This post will focus on the stove pipe clearances required for safe operation.
These are based on standards developed by the National Fire Protection Association (NFPA) that are the basis for many local building codes.
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. 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 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 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.
Additional Precautions
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 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.
Installation of a wood stove is best left to the professionals. Before installing a wood stove, seek advice from your stove dealer, your local building inspector or fire department. It is also a very good idea to check with your insurance agent. Your insurance provider may have its own specifications for installation and, since you will be changing the method of heating your home, your insurance agent must be notified in order to maintain fire insurance coverage on your home.
This information comes from Michigan State University Extension
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