The necessary clearances from combustible materials are marked on each section of a UL-listed prefabricated chimney. For the insulated double wall-type chimney, the minimum clearance is usually two inches.
(1) Exterior metal chimneys over eighteen inches in diameter, for equipment of any operating temperature, shall have a clearance of at least four inches, and those eighteen inches or less in diameter shall have a clearance of at least two inches from a building wall of any combustible construction.
This rule means that your chimney's shortest side needs to be at least 3 feet above the roof penetration, and its top has to be 2 feet higher than any part of the building that's within 10 feet.
Flue Pipe Clearance Requirements
Your flue pipe needs proper clearance from combustible and non-combustible materials for safety. You'll need at least three times the pipe's diameter for clearance from combustibles.
The positioning of the flue needs to be (a minimum of): 300 mm away from an opening window or air vent. 25 mm below guttering, drain pipes or soil pipes. 300 mm above the ground, roof or balcony level.
NFPA dictates a minimum longitudinal flue space of 6” to allow fire ventilation along with water penetration from the sprinkler system above. This design is also driven by the commodity that is being stored.
Oil-fired and natural gas appliances that create draft hood flue gasses that do not exceed a temperature of 570°F, or 926°F for 10 minutes in an over-fire emergency, can be vented using Type L vents. Typically, 3 inches of clearance must be left between the vent and any combustible material.
For interior chimneys, a 2 inch minimum air space between the chimney and combustibles must be maintained. An interior chimney is defined as any chimney having 1 or more walls inside a structure. For exterior chimneys, a 1 inch minimum air space must be maintained between the chimney and combustibles.
The boiler flue terminal should be positioned away from doors, windows or other openings. There should be a space of at least 300mm above, below or to the side of any opening. Harmful gases should be properly expelled from the property, so they cannot re-enter.
How much space to leave around a wood burner? For non-combustible materials, the typical minimum distance or clearance required from the front and rear of the stove's external surface to surrounding walls is 150mm. This clearance requirement is for both freestanding stoves and wood burners installed within a recess.
The flow area of the largest common vent or chimney shall not exceed seven times the area of the smallest draft hood outlet. Typically: many water heaters use a 3" flue, the largest area to connect the water heater should be 49" in area or an 8" x 8" chimney tile or 7" round chimney.
Combustible framing shall be not less than 2 inches (51 mm), but shall be not less than the distance specified in Sections 2111 and 2113 and the California Mechanical Code, from flues, chimneys and fireplaces, and 6 inches (152 mm) away from flue openings.
As you extend your flue you are extending the pressure difference which can only improve the draw and performance of the chimney and stove. This also ensures the draw is not impeded in any way by adjacent buildings and trees which will affect the direction of air across the top of your flue.
Regulations require the flue to be: 300mm away from any openable window or vent. 300mm away from any door.
(A) All wood floor and roof framing shall be kept at least 2 inches away from the chimney masonry, except when 8 inches of masonry is used outside the flue lining, in which case the framing may be built flush with the chimney masonry.
2113.19 Chimney Clearances
Any portion of a masonry chimney located in the interior of the building or within the exterior wall of the building shall have a minimum airspace clearance to combustibles of 2 inches (51 mm).
NFPA requires 6” of transverse flue space. Longitudinal Flue Space: Orientating yourself to the end of the row of racking. This is the space between each row of back-to-back systems going perpendicular to the direction of loading. The NFPA requires a 6” minimum of longitudinal flue space.
Double wall flue pipes have to be installed in accordance with the manufactures installation instructions. ( generally clearance to combustibles is 6 inches. ) Single wall flue pipes have to comply to CSA B365 requirements. ( generally clearance to combustibles is 18 inches. )
Flues should be at least 25mm from any combustible material (measured from the outer surface of the flue wall, or the outer surface of the inner wall in the case of multi-walled products).
The flue must be at least 1.5 times its external diameter away from the heat shield, the heat shield must extend at least 1.5 times the flue's external diameter to each side of the flue, and there then has to be an air gap of at least 12 mm between the shielding material and the combustible material.
STOVEPIPE PROTECTION: Stovepipe, and chimney connectors, must also be a certain distance from both combustible walls and ceilings. The NFPA calls for an 18" clearance to combustible walls for single wall stove pipe(opens in a new tab).
Code has long required a 2" air space between the outside of a masonry chimney and any combustible material. And that air space "shall not be filled, except to provide fire blocking", reads the current International Residential Code (IRC)*.
Longitudinal Flue space is the gap between back-to-back rows of pallet rack, essential for preventing blockage. Proper spacing prevents dislodged products from obstructing the flue. Transverse Flue spaces are gaps between pallets and rack frames. Stacking pallets less than 6″ apart blocks this space.
The vent terminal of a direct-vent appliance with an input of 10,000 Btu per hour (3 kW) or less shall be located at least 6 inches (152 mm) from any air opening into a building, and such an appliance with an input over 10,000 Btu per hour (3 kW) but not over 50,000 Btu per hour (14.7 kW) shall be installed with a 9- ...
When installed the minimum clearance between the terminal and any adjoining vertical walls or obstructions must be at least 500mm. The terminal must not be installed within 600mm of an openable window, air vent or any other ventilation opening.