Chimney height & horizontal clearance specification FAQs set #2:
These questions & answers discuss required height or other clearance distances for chimneys at rooftops, patios, decks, terraces, and between flues or between a chimney and nearby windows, doors, neighbours. .
This article series describes the height requirements for chimneys, including rooftop clearances and overall chimney height necessary for proper chimney draft and function and for fire safety. We describe what can go wrong with chimneys that are not built to proper height or with proper clearances from other building features, including improper or unsafe heating appliance or fireplace or woodstove operation, odors, soot, draft issues, etc.
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These questions about chimney or flue height & clearance from various building features were posted originally at CHIMNEY HEIGHT & CLEARANCE CODE
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On 2017-08-10 by (mod) how to determine the required chimney height over a rooftop deck or patio
There are two different concerns in answering your excellent question, Dave.
1. The minimum chimney height above a terrace has to address fire and safety clearances from roof surfaces and building openings, as given in CHIMNEY HEIGHT & CLEARANCE CODE inspectapedia.com/chimneys/Chimney_Height_Codes_Specifications.php - which is this very article
That can be as little as one foot over a flat roof, though we warn that if that height results in an overall too-short chimney flue, such as would occur at a one-story flat roofed building whose chimney just extends up a foot over the roof surface, the appliance vented in that chimney may be unsafe due to inadequate draft.
2. Additional height or provisions might be needed to protect occupants on a terrace or patio from chimney smoke and fumes - those are not fire safety issues. You may not find all possible occupied spaces codified in chimney height or clearance codes.
In that case I'd apply at least the minimum clearance distances intended to prevent flue gases from entering a building window or door that might be opened.
Here is an example from paragraph 503.8 Venting system termination location, in the 2003 International Fuel Gas Code that you can find at BUILDING CODE DOWNLOADS
A mechanical draft venting system, excluding direct-vent appliances, shall terminate at least 4 feet (1219 mm)below, 4 feet (1219mm)horizontally from, or 1 foot (305 mm) above any door, operable window, or gravity air inlet into any building.
The bottom of the vent terminal shall be located at least 12 inches (305 mm) abovegrade.
3. The vent terminal of a direct-vent appliance with an inputof 10,000 Btu per hour (3 kW) or less shall be located at least 6 inches (152 mm) from any air opening into abuilding, and such an appliance with an input over 10,000 Btu per hour (3 kW) but not over 50,000 Btu perhour (14.7 kW) shall be installed with a 9-inch (230 mm) vent termination clearance, and an appliance with an inputover 50,000 Btu/h (14.7 kw) shall have at least a 12-inch (305 mm) vent termination clearance. The bottom of the vent terminal and the air intake shall be located at least 12 inches (305 mm) above grade
You could "interpret" these guidelines to mean that the chimney should terminate high enough over the terrace or rooftop patio that people are not exposed to nor within four feet of the chimney terminus. Using a person height of six feet you'd get to a ten foot chimney height over the terrace.
Of course the final authority is your local building code inspector. Ask your building department for an opinion and do us the favor of telling us by another comment here just what you're told.
On 2017-08-10 by Dave How high does a flue need to be if there is a terrace on the roof?
How high does a flue need to be if there is a terrace on the roof?
On 2017-08-06 by Ryan McNair - the 3-2-10 chimney code summarizes NFPA specifications
The code is 3,2,10. A chimney must be a minimum of 36" tall and 2 feet above anything within 10 feet of the top of chimney. That is NFPA code clearance.
[Below added by editor for clarification]
On 2017-05-14 by (mod) chimney height restrictions for a bungalow with chimney on top of roof line
If the chimney exits roof at the ridge it needs to extend at least two feet above the surface of the ridge. If the chimney exits the roof at some lower point then if you draw a horizontal line from the top of the chimney flue opening to the point at which that line would touch the roof, but distance must be ten feet or more. That requirement could also mean that you need to extend a chimney height.
Purpose of these rules is principally fire safety but also chimney draft may be affected
On 2017-05-14 by Ellie
What are the chimney height restrictions for a bungalow with chimney on top of roof line..?.
On 2017-04-04 by (mod) chimney clearance for combo units?
What do you mean by "combo unit"?
You may want to see CHIMNEY CLEARANCE to NEIGHBORS - http://inspectapedia.com/chimneys/Chimney_Clearance_to_Neighbours.php
On 2017-04-04 by Adam
I have a combo unit at roof top that is within 4 feet from chimney that is the same height of combo unit. Is there a certain height the chimney needs to be to be close to combo unit
On 2017-03-16 by (mod) adjacent or near-adjacent chimney flues
I think you're asking about adjacent or near-adjacent chimney flues - please check that section of the article above.
On 2017-03-16 by Elizabeth
Is a heat furnace flute or vent that's 3 foot tall on the roof and is several feet away from the chimney, considered a "structural component?" Would the chimney have to be 2 foot taller in height than the heat furnace flute? The house was built in 1963. Thank you.
On 2017-01-31 by (mod) The ten-foot / two-foot chimney rule:
The ten-foot / two-foot chimney rule:
The top of a chimney must also extend at least two feet above a roof, ridge, or other structural component that is ten feet or less away in horizontal distance.
"Any other structural component" would include the gable end of your house.
This height is shown by the vertical blue arrow shown at the left hand chimney in the sketch in the article above and the ten foot line is shown in black in the same drawing.
On 2017-01-31 by martin
please could you let me know the distance our neighbours woodburning flue should be away from my gable end
On 2017-01-27 by Classic chimney
I have a client that has a 9" stainless steel liner with a lenox gas boiler 6" output 80000 btu with a water heater 3" 40000 btu, inspecter said he feels a downdraft and system needs to be reduced do i have to removethe 9" to install a 6" thank you
On 2017-01-01 by (mod) 16" separation between adjacent metal chimney flues
Tim in the article above our source cites 16" separation between adjacent metal chimney flues. Your local code inspector or the manufacturer of your chimney product may have a different requirement.
Please also see FLUE SEPARATION REQUIREMENTS at http://inspectapedia.com/chimneys/Masonry_Chimney_Flue_Separation_Code.php
On 2016-12-29 by Tim in Wisconsin
I am constructing a chimney chase that will enclose 3 double wall stainless chimneys. How far apart do they need to be? At the exit point of the chase, what different heights do the chimney caps need to be?
On 2016-12-05 by (mod) maisonette home chimney clearances
I am guessing that you refer to a maisonette home - a small apartment on two or more floors of a larger building and with its own entrance.
We cannot assess chimney, heater, nor home safety conditions by e-text and your note leaves me frightened.
I do not understand your question nor situation. But because there are life safety concerns - fire and gas poisoning risks - if you have ANY reason to suspect that there is a fire, a chimney leak, or you see or smell smoke you should get everyone out of the building immediately and call emergency services from a safe location.
On 2016-12-05 by Anonymous
I Live in a 1950 type Masonet. My downstairs f/place has been removed,and the old back boiler removed. (Gas).
Upstairs there is still in use solid fuel fire.My openING has been blocked up,with a small air vent.When there is alive fire I get awful smell of smoke in my bedroom.,I have now blocked the air vent in my bedroom.it's right to have this situation on going.With regards Mr g what pudney
On 2016-11-27 by (mod) Gas Appliance input BTU De-Rating Guidelines for High Altitude Installations?
Good Question Jason. Using the model Fuel Gas Code, Chapter 5,
What are the Gas Appliance input BTU De-Rating Guidelines for High Altitude Installations?
504.2.5 High-altitude installations. Sea-level input ratings shall be used when determining maximum capacity for high altitude installation. Actual input (derated for altitude) shall be used for determining minimum capacity for high altitude installation.
Translating, I think this means that since a chimney size and design must meet the fuel and input BTUh ratings of the appliance vented through it, at high altitude you're being given guidance on which BTUh numbers to use.
Between 6000 and 11,000 feet of altitude above sea level, you must follow the instructions provided by the manufacturer of the heating appliance(s) involved.
I've read that typical BTUh de-rating percentages are as follows:
De-rate the input BTUh by 2% per 1000 feet [presumably that's per 1000 ft. above 6000] for forced-draft appliances
De-rate the input BTUH by 4% per 1000 feet (as above) for natural draft appliances.
Watch out: depending on where you live, your gas supplier may also be using a gas that itself has more or less BTUs per unit volume of gas than standard. Be sure to check with your gas supplier. They'll know the exact situation for where you live.
Also see this Rheem PDF on water heaters at high altitude
On 2016-11-27 by Jason specification adjustments for high altitude applications
I was wondering if there are specification adjustments for high altitude applications . I live at approximately 7800 feet above sea level. Thank you for providing this information!
On 2016-10-25 by (mod) Washington State's Fire Code
Washington State has adopted and modified the national fire code. Here is a current copy of Washington State's Fire Code
I don't see a specific mention of tree-to-chimney clearance but the model code Chapter 6 states a 10-foot requirement for clearance from tree to chimney; I'd assume this is from the closest part of the tree to the closest part of any chimney.
"a chimney shall be pruned to maintain a minimum horizontal clearance of 10 feet "
Here are excerpts from the ICC International Wildlife-Urban Interface Code that make sense to me regarding chimney safety:
Section 604, Maintenance of Defensible Space
604.4 Tees: Tree crowns extending to within 10 feet (3048 mm) of any structure shall be pruned to maintain a minimum horizontal clearance of 10 feet (3048 mm). Tree crowns within the defensible space shall be pruned to remove limbs located within 6 feet (1829 mm) above the surface adjacent to the trees.
604.4.1 Chimney Clearance: Portions of tree crowns that extend to within 10 feet (3048 mm) of the outlet of a chimney shall be pruned to maintain a minimum horizontal clearance of 10 feet (3048 mm)
604.4.2 Deadwood removed: Deadwood and litter shall be regularly removed from trees.
On 2016-10-25 by Anonymous Washington State Fire Codes, regulations, guidelines for safe proximity of chimney to trees
Would like to know any Washington State Fire Codes, regulations, guidelines for safe proximity of chimney to trees.
On 2016-10-15 by Annie
Thank you for all the information. I just asked a company rebuild the chimney and I felt something wrong with it. then I found this web to see, it is too short. only about two layer brake over the roof. I sent massage to the guy, he said what they did is exactly follow the code. How and where can I ask somebody to give a official document to show the chimney is follow the code or not. thank you very much for your help.
On 2016-10-11 by Paul Balga
Is it possible to remove the masonry from around a clay liner and still be in compliance with code? I am putting on a new metal roof and installing a high efficiency furnace, and want to remove the chimney to about 18" above the roof line. In case the roof install is ready before the furnace is, I don't want to damage it by dropping bricks on it during the chimney demolition. Knocking the clay liner down later should be a simpler task.
On 2016-09-29 by (mod)
If you mean the chimney is 20 ft. horizontal distance from the nearest other building wall or roof, that should be ok; you might need a taller chimney to improve draft as well as adding a chimney cap; I'd ask for an opinion from your local certified chimney sweep, as there could be other reasons for bad draft such as a leaky cleanout door or inadequate combustion air supply. Also search InspectApedia for CHIMNEY DRAFT to read more.
On 2016-09-28 by Wayne Matthews
My single story bonus room fireplace is 20'from the two story main house. The current chimney is 8' feet above the roof line at the chimney location (at the rear wall) and 5 feet above the bonus room roof height where it attaches to the main house. It does not draw well. It does not have a cap. I understand that a cap would help but what about chimney height? Is the 20'distance from the second floor enough or do I need to raise the chimney height and put a cap on it?
On 2016-09-25 by kelley
Similar question, I have an attached 2 car garage (1st roof line; if I put a wood stove in my garage must the chimney pipe be above the 2nd floor roofline?
On 2016-09-21 4 by tim
I want to place a wood burner stove in basement and go out side of house. Must my chimney go up through entire second story roof, or just first floor roof? It will not be 10 ft away from any thing unless I leave the basement wall and go outwards 10 ft. That would look poor.
On 2016-09-13 by Anonymous
For the case I think you are describing the top of the chimney outlet flue opening should be 2 feet above the ridge.
I'm confused...if my chimney runs up the side of the house and meets the roof at the ridge line. Does the height need to be 3 or 2 feet above the ridge line§§
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