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Mobile ViewCHIMNEY INSPECTION DIAGNOSIS REPAIR Abandoned Chimneys - Indoor Inspection Abandoned Chimneys: Outdoors Angled Chimney Flues Attic Chimney Inspection BACKDRAFTING HEATING EQUIPMENT BAROMETRIC DAMPERS Blocked Chimney Flues Bracket Chimney Collapse & Fire Risks B-Vent Chimneys B-Vent Clearances Table CARBON DIOXIDE - CO2 CARBON MONOXIDE - CO CHIMNEY INSPECTION & REPAIR GUIDE Chimney Cap & Crown Inspection CHIMNEY CHASE Construction & Defects Chimney Cleaning Advice, Procedures Chimney Cleaning Fraud Warning Chimney Cleanout Doors Chimney Components Definitions Chimney Crack & Collapse Risks, Repairs Chimney Crack Detection & Diagnosis Chimney Draft & Performance CHIMNEY FIRE ACTION / PREVENTION Chimney Flashing Mistakes & Leaks CHIMNEY HEIGHT & CLEARANCE CODE Adjacent Metal Chimney Separation B-Vent Clearances Table Chimney Too Short Chimney Height Extensions Chimney Height for Types L & Type B Vents Fire Clearances for Masonry Chimneys Fire Clearances for Metal Chimneys FIRE CLEARANCES, Single-Wall Metal Flues Masonry Chimney Roof Clearance Wood burning Fireplace Roof Clearance Chimney Height Extensions Chimney Inspection Checklist Chimney Inspection: Flue Interiors ChimScan: Inspecting Flues by Cameras Chimney Inspection Indoor Procedures Chimney Inspection Outdoors From Ground Chimney Inspection Outdoors at Rooftop Chimney Leaning, Separation, Movement Chimney Repair Fraud Warning Chimney Repair Methods Chimney Safety - CPSC Alert Chimney Shoulder Leaks Chimney Spalling, Exterior Chimney Sweeps Chimney Types & Materials CO2 TOXICITY COALSTOVE SAFETY COMBUSTION AIR DEFECTS COMBUSTION AIR for TIGHT buildings COMBUSTION GASES & PARTICLE HAZARDS COMBUSTION PRODUCTS & IAQ COMPLETE COMBUSTION, Stoichiometric CREOSOTE FIRE HAZARDS Dead End Chimney Flue Hazards Definitions of Chimney Types & Parts DIRECT VENTS / SIDE WALL VENTS DRAFT HOODS - gas fired DRAFT MEASUREMENT, CHIMNEYS & FLUES DRAFT REGULATORS, DAMPERS, BOOSTERS EFFLORESCENCE, Salts & White / Brown Deposits EMERGENCY RESPONSE, IAQ, GAS, MOLD FIRE CLEARANCES INDOORS Fire Clearances for Masonry Chimneys Fire Clearances for Metal Chimneys FIRE CLEARANCES, Single-Wall Metal Flues Fire Clearance Wood & Coal Stove Flues FIREPLACES & HEARTHS Fire stopping at Chimney Passage Through Floors FLAME COLOR, BLUE vs YELLOW COMBUSTION FLUE SIZE SPECIFICATIONS Flue Separation Requirements Flue Tile Damage in Chimneys Flue Vent Connectors - Boilers, Furnaces Fuel Changes for Heating Appliances HEATING COST FUEL & BTU Cost Table HEATING INSPECTIONS HOME HEATING SAFETY HEATING SYSTEMS INDOOR AIR EMERGENCY RESPONSE Lennox SAFETY WARNING Metal Chimneys & Flues Moisture / Frost Damaged Chimney Nanomaterials Hazards NOISE / SOUND DIAGNOSIS & CURE ODORS & SMELLS DIAGNOSIS & CURE ODORS FROM HEATING SYSTEMS OIL HEAT SAFETY INSPECTIONS PLASTIC HEATER VENTS Safety Recalls, Chimneys, Vents, Heaters Shared Chimney & Shared Flue Hazards STAIN DIAGNOSIS on BUILDING EXTERIORS STAINS on/near CHIMNEYS Three-Sided Chimneys: Problems Transite Pipe Chimneys & Flues UNLINED FLUE INSPECTIONS WOOD, COAL STOVES & FIREPLACES WOOD STOVE SAFETY More Information |
This article describes the height requirements for chimneys, including rooftop clearances and overall chimney height necessary for proper chimney draft and function and for fire safety. These articles on chimneys and chimney safety provide detailed suggestions describing how to perform a thorough visual inspection of chimneys as well as chimney construction & repair methods. InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers nor with topics or services discussed at this website.© Copyright 2012 InspectAPedia.com, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website. Outdoor Chimney Height & Clearance RequirementsSee CHIMNEY HEIGHT & CLEARANCE CODE. Also see Chimney Height Extensions and see the US CPSC warnings at Chimney Clearance & Condition Safety. Additional chimney clearance and safety information is at A variation on a "too short" metal or masonry chimney is a chimney that may look tall-enough to some folks but which lacks adequate clearance from a nearby roof slope, as we illustrate and explain in the text below. Check the chimney top for damaged masonry (or rusted metal), a missing cap, damaged, cracked, or missing top seal or crown on the top of a masonry flue, and here, an important discovery (at least in some jurisdictions) is whether or not the chimney is single wythe or thicker masonry and whether or not the chimney has (or perhaps needs) a chimney liner. Chimneys Too Short - What is "too short" and What Problems Occur?
A chimney that is too short is unlikely to vent properly and it may also be a serious fire hazard to the building, risking setting the roof on fire. The photo at above left is a too-short masonry chimney (with no cap and other worries). A horizontal line (blue in our photo) drawn from the chimney top to where it would touch the roof surface was just about one foot instead of the required ten feet OR two feet above the ridge. A "Hidden" "too-short" Chimney Specification: Distance Above the Flue Collar - can lead to inadequate draftNFPA-211 1-8.2 specifies that
Inspecting from outdoors you may not be sure if a chimney violates this rule or not - you'll also need to look inside at the heating equipment and at the building structure, ceiling height distances etc. to make an actual measurement. Too-Short Heating Flue Can Mean Sooty Oil Burners and Puffbacks or Dangerous CO Poisoning Hazards
Carbon Monoxide Poisoning Hazards from Too-Short ChimneysParticularly with gas fired appliances, the lack of adequate draft for any reason, including a chimney flue that is too short, can result in improper combustion and the production of dangerous, potentially fatal carbon monoxide gases. And the same inadequate draft that affects combustion in the heater can increase the risk that the gas backdrafts out into the buildings. NFPA 211 1.7.1 specifies:
Draft-Fixes for "Too Short" ChimneysAn obvious fix for a chimney that is too short to meet the fire safety clearances mentioned earlier is that must be extended above the roof for fire safety. But in some installations, such as a heating appliance installed in a one story low ceiling structure, the chimney may meet the fire clearance specifications (NFPA 211 1-8: Termination Heights) but it not be tall enough to develop adequate draft (NFPA 211 1-7). In this case it is permitted (NFPA 211 1-7-2.) to use a draft inducer fan ("a mechanical draft system of either forced or induced draft design") to meet the draft requirements. Watch out: if you use a draft inducer system the installation must assure that the heating appliance won't run if the draft inducer is not running. Most if not all modern mechanical draft or draft inducer systems include this safety feature as do direct-vent or side-wall vented appliances that use no chimney at all (another solution to some chimney problems). Also see COMBUSTION AIR for TIGHT buildings. Bachrach, Field, & Tjernlund are examples of companies providing draft inducing or mechanical draft boosting equipment and direct-venting equipment that skips use of a chimney altogether. [14[15[16] Required Chimney Height Above Roof Surfaces or RidgesRoof Clearances for Chimneys 10 Ft. or more distant from the Ridge
Roof Clearances for Chimneys Less than 10 Ft. (3.1m) from the RidgeThe photo at above right is a too-short metal chimney that is less than two feet above the ridge. This chimney fails both the ten-foot rule (the blue line) and the two foot rule (the red line). A horizontal line drawn from the chimney top just touches the roof ridge.
We edited the short chimney photo to extend it up to meet the following roof clearance requirements (see edited photo at left): Watch out: We also notice that the chimney cap is discolored on this metal flue - possibly indicating an overheated appliance or other unsafe condition. Did you also notice that the sides of the chimney flashing are on top of rather than under the roof shingles? Where to Make Measurements When Checking Chimney ClearancesAnother question that has come up is "do we have to measure from the chimney cap or from the (lower) opening at the top of the flue? In specifying clearances the NFPA 211 refers to the "Highest Point" of the chimney. Our reading of the NFPA and codes is that
Roof Clearances for Wood Burning Fireplaces
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Wood burning Fireplace Roof Clearance RequirementsCarson Dunlop's sketch at left shows that the minimum chimney height above a wood burning fireplace is 15', and that a shorter minimum of 5' may be acceptable above the draft hood of a gas furnace is allowed in some jurisdictions. |
Adjacent Metal Chimney Separation RequirementsIn addition to the requirement for safety fire clearance from rooftops and other building components, separate metal chimneys that are too close to one another may cause damage resulting in poor chimney performance or an unsafe chimney. Carson Dunlop's sketch at left shows that metal chimneys should be at least 16" (that's 16 inches) apart to avoid damage. |
Table of Type B-Vent Rooftop Clearance RequirementsThe 1992 Vent Sizing Tables require that all Type B gas vents terminate above the roof with a listed cap or listed roof assembly in accordance with the manufacturer's instructions. Vent caps 12" and smaller may terminate a distance above the roof if 8 feet or more away from a vertical surface as follows: ROOF PITCH - rise/run in inches MINIMUM HEIGHT* Flat to 7/12 - 1.0 foot above the roof surface 7/12 to 8/12 - 1.5 feet above the roof surface 8/12 to 9/12 - 2.0 feet above the roof surface 9/12 to 10/12 - 2.5 feet above the roof surface 10/12 to 11/12 - 3.25 feet above the roof surface 11/12 to 12/12 - 4.0 feet above the roof surface * Continues to 21/12 pitch at 8.0 feet Vent caps larger than 12" must be located at least 2 feet above the highest point and 2 feet higher than any portion of the building within a horizontal distance of 10 feet. For details about metal chimneys see Metal Chimneys & Flues |
Why would my fireplace smoke up the house during the time I have a fire. It's a masonry chimney. Also, my chimney is not 2 foot higher than the peek of the roof. - George Angell
I get smoke in my basement when I first light my fireplace. Both my fireplace flue and furnace flue are at the same height. I also had my co detector go off the other day. Is the flue height being the same, be the reason for those 2 problems? TKS - Dom 4/11/12
Dom and George:
If your flue is cold it can take a while for the chimney to heat up enough to establish a good draft over a fireplace. To help things get going we often
The chimney should be extended to be at least 2 feet above the ridge if the chimney is at or close to the ridge, or it should meet the height requirements shown in the sketch at page top.
If your chimney is too short it may not only result in inadequate draft (and improper heating system operation) but it can also be a fire hazard to the structure.
We gave a 12/12 pitched roof and want to put a wood burning stove near the outside edge of the house (not near the peak) - is there ANY configuration of chimney that will not have 12 feet (or more) of pipe sticking out of the roof line?
Routing the chimney flue pipe toward the peak is not really an option it would basically have to come up near the outside eaves - clearing 2 feet any roof surface within 10 feet means at least 12 feet of pipe as far as I can tell. Are powered chimney vents an option? - Matt
Matt: a line drawn horizontally from the top of the chimney to a point where that line would touch the roof surface needs to give you ten feet in distance for fire safety. If your roof pitches up steeply that may mean you need a rather high woodstove chimney to be safe. And you may need bracing.
I've not found references to power vent exhausts for woodstoves. Certainly it is not at all likely that a power-vented chimney would be more fire safe and thus would not need the same fire clearances as other chimneys and flues.
i have a two story home. i just built a single story room off this home with a wood stove. what is the clearance from the chimney pipe to 2nd story window? it is already 2 feet above the ridge and 12 feet from the 2nd story windows - Charlie
Charlie I'm not sure I understand the picture and measurements of the addition you describe. If your chimney is two feet above the ridge of the upper roof it would certainly not be too close to any windows.
If your chimney is two feet above the ridge of a roof over the one story addition, if you can't get more than 12 feet of horizontal distance between chimney and windows of the upper floor, you probably need to extend the chimney above the upper roof, following the ten-foot horizontal line rule we describe above.
Otherwise in at least some conditions, someone is going to open an upper floor window and find smoke blowing into the room.
I want to add a pitched roof to an existing home for a screened in porch. The point of the gable would go up against the existing chimney. Is that acceptable as long as the point of the gable (the highest point of the addition) is still 3.5 feet below the top of the chimney?
Dave that sounds OK to me, just be sure to properly flash against the chimney or you'll have leaks. That is, if the ridge of the lower roof, where it abuts the existing chimney, is three feet or more below the chimney top, you've met that clearance requirement (the three-foot chimney clearance rule).
My masonry chimney extend 2' above the top of the pitch. Does it have to be extended to 3' above to comply with the NBC? - Frank
Frank,
Some building code officials, builders, and chimney professionals call this simple chimney fire clearance code the
"two-foot, three-foot, ten-foot rule for chimney heights" - which we explain as follows:
Your chimney top to roof clearance (for fire safety) is correct if the chimney height extends:
Take a look at the chimney height clearance requirements sketch at the top of this page. The only confusing detail in that sketch is that the "ten foot chimney height rule" horizontal line was shown as drawn mid way down the chimney - really that line is drawn from the chimney TOP to the nearest roof surface.
I have an "A" frame cottage with a new metal roof. The woodstove has a 10" insulated metal chimney which extends above the roofline by approximately 7 ft. and is above the peak by maybe 1 ft.
Bruce:
Ok, so technically your flue is one foot short; perhaps given the very steep roof and that it's metal, I'm not as worried as I'd be otherwise, but it's possible that the chimney is not fire safety and code compliant for a second reason: if you were to draw a horizontal line from your chimney top towards the ridge, and if the horizontal distance from the top to the ridge is less than 10 feet, then properly your chimney needs to go up another foot.
On the other hand if the horizontal distance from your chimney to the ridge is ten feet or more, you're ok as is.
At CHIMNEY HEIGHT & CLEARANCE CODE you can find articles on required chimney heights above the roof line.
Refer to the sketch titled "Masonry Chimney Roof Clearance Requirements".
The line that is drawn that illustrates the 10 feet run is placed in the middle of the chimney. Depending on where you place this line has a HUGE impact on how high the chimney needs to be. If this line were drawn on the top of the chimney it would need to be substantially taller. Where am I supposed to take the measurement from?? - Jason Vetter 3/11/12
Jason, you are dead right - the page top chimney to roof clearance sketch
has long bothered me too, leading to other photos and sketches on this
page that showed the required distances correctly. We have reviewed, edited, and adjusted all of the chimney clearance measurement drawings and photos in the article above to clarify these distances.
The original NFPA-211 drawings on which the page top sketch was based were
equally confusing.
For chimneys that are 10 Ft (3.1 m) or MORE away from the roof ridge (measured
at the up-roof side of the chimney):
Notice that I use the words "any roof surface" in this explanation. That means that if there are other nearby structures, say a dormer, the same clearance rules apply,
For chimneys that are LESS than 10 feet from the roof ridge (measured at the up-roof side of the chimney)
and
Another question that has come up is "do we have to measure from the chimney cap or from the (lower) opening at the top of the flue? In specifying clearances the NFPA 211 refers to the "Highest Point" of the chimney.
Thanks so much again for the reminder to fix this, Jason. We welcome reader questions and ocmments. We are dedicated to making our information as accurate, complete, useful, and unbiased as possible: we very much welcome critique, questions, or content suggestions for our web articles. Working together and exchanging information makes us better informed than any individual can be working alone.
I just had a home inspection done and the inspector said that my furnace pipe that gose through the roof needs to be extended (metal pipe) is that something I can do myself - Rusty 4/18/12
Sorry Rusty but not to be glib, i don't know your capability. The chim materials and extension need to meet code, be secure and od correct materials. Youncould get a bid from a chi net person whonis certified.
I live in a Cape Cod style home. We recently had a chimney fire and a subsequent WETT inspection. I was told that the chimney does not meet code and is not 2 feet taller than the nearest structure. I am wondering what the code was in 1990 when the house was built? We live in southern Ontario. - Sara 1/10/12
Hi, I've found an answer for the "what was the code 21 years ago" question. Now I'm wondering what I can do re. the chimney that is apparently 8" below code. Do I have to pay to have it fixed even though it's not my fault? No one has ever mentioned the 2' rule before and I worry that we've had a chimney that is unsafe for 21 years. The inspection cost $339 and I need to know how I can fix this situation. I can't use the fireplace now. Sara 1/12/12
Sara the risk of a house fire is deadly serious and deserves a proper and safe chimney. The fact that no one mentioned chimney safety to you is a bit cloudy to me - unless you had a professional inspection or service performed on the home I'm not sure who was on site before a chimney fire or related problem to examine the home and and inform you.
The question of who pays for repairs is one to discuss with your attorney.
My masonary chimney extend 2' above the top of the pitch. Does it have to be extended to 3' above to comply with the NBC? - Frank 9/6/11
Some building code officials, builders, and chimney professionals call this simple chimney fire clearance code the
"two-foot, three-foot, ten-foot rule for chimney heights" - which we explain as follows:
Your chimney top to roof clearance (for fire safety) is correct if the chimney height extends:
Take a look at the chimney height clearance requirements sketch at the top of this page. The only confusing detail in that sketch is that the "ten foot chimney height rule" horizontal line was shown as drawn mid way down the chimney - really that line is drawn from the chimney TOP to the nearest roof surface.
if i install an older stove in my shop , will i suffer any code violations if putting in everything myself , using new single wall below and tripple out the metal roof with one inch space between wall and durarock used as a heat spacer ? - Mike 1/5/12
Mike, possibly yes.
In many U.S. & Canadian jurisdictions a building permit and approval inspection are required for the installation of woodstoves and other heating appliances.
Questions & answers about chimney height & clearance requirements to comply with building codes and fire safety.
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CHIMNEY HEIGHT & CLEARANCE CODE
Adjacent Metal Chimney Separation
B-Vent Clearances Table
Chimney Too Short
Chimney Height Extensions
Chimney Height for Types L & Type B Vents
Fire Clearances for Masonry Chimneys
Fire Clearances for Metal Chimneys
FIRE CLEARANCES, Single-Wall Metal Flues
Masonry Chimney Roof Clearance
Wood burning Fireplace Roof Clearance
Chimney Height Extensions