Short metal chimney (C) Daniel FriedmanChimney Height & Separation FAQs
Q&A Set #3 on chimney height & clearance distances

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Chimney height & horizontal clearance distance questions & answers, set #3:

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 also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

FAQs#3 Chimney Height & Clearance Distance Codes

These questions about chimney or flue height & clearance from various building features were posted originally at CHIMNEY HEIGHT & CLEARANCE CODE

[Click to enlarge any image]

On 2018-03-08 by (mod) - gambrel roof chimney clearance design

Mike, your chimnney top needs to clear the 10 foot rule - 10 ft. horizontal distance from the top of the flue opening to any roof surface.

Do not copy this incorrect metal chimney clearance to a gambrel barn roof that I pass by outside Two Harbors Minnesota.

But as you can see, you'll need to have sufficient horizontal extension if you intend to avoid passing through the eaves of the lower-sloped gambrel roof section.

On 2018-03-08 by Mike

I want to go thru long wall on my Gambrel roofed barn.

How do to measure the chimney height against the 2 separate pitches. The trusses are 12’ tall. The lower steeper section is a 15 1/2-12 pitch and the upper is 3 1/2-12. So I want to go out past the 12” eave and straight up

On 2018-02-25 02:25:51.027654 by (mod) -

The top of the flue opening should be at least 10 Ft (3.1 m) away from any roof surface (or other structure) as measured by a horizontal line drawn from the top of the chimney flue opening to where it would touch the roof surface. (The horizontal red arrow in our sketch)

On 2018-02-25 by Juan Rodriguez

How far away does a metal chimeni need to be away from the out side Wall in Rochester ny zip code 14606 ?

On 2018-02-14 by (mod) -

Sounds like it to me, for fire safety

but you might also look at your bath vent fan to see if you can fit a model that is protected against backdrfting.

On 2018-02-14 by A DM HOME SERVICEs Mckibbin03 Phone

I live in a semi detached house with a single flat roof extension with a bath room sky lite and extractor out let our naigbour also has a flat roof extension too they have recently had a wood burner fitted we are having problems with smoke and fumes smells in the bathroom the flue height roughly a meter from the roof surface dose the flue need to be extended

On 2018-02-12 by (mod) -

Chimney height clearance 2 3 10 foot rule illustrated © D Friedman at

All readers: general guideline:

The National Fire Protection Association Standard #211 states:

“Chimneys shall extend at least three feet above the highest point where it passes through the roof of a building, and at least two feet higher than any portion of a building within ten feet.”

On 2018-02-12 by (mod) -


You can probably install at 30 or 45 off of vertical - depending on local codes and providing you follow the manufacturer's instructions that include limits on both length and number of elbows.

Please see ANGLED CHIMNEYS at where I correct my earlier remarks and give a detailed answer to your question.

On 2018-02-12 by John

How about 30 degrees I read on another forum that was max

I have an attached garage that I want to put a oil fired furnace in. I am curious if I’m allowed to put flue pipe at a 45degree angle in attic space to get horizontal distance from house to the required 10 feet

On 2018-02-09 by (mod) -


Please see CLASS A CHIMNEYS, MetalBestos™ at

On 2018-02-08 0 by (mod) - a long usually horizontal flue vent connector is a common source of clogs or blockage,

I agree that a long usually horizontal flue vent connector is a common source of clogs or blockage, and draft problems and is even more of a problem if it runs through an inaccessible area meaning it's not likely to be inspected or cleaned.

I would also look for secondary Cruz of a history of draft problems chimney leaks or chimney blockages such as signs of backdrafting or damage to a metal flue vent connector

On 2018-02-07 by Phil

Hi, i just bought a house and im really curious about the chimney. From my basement, the chimney goes under my garage floor with a light angle but its almost consider as a flat surface. It goes up about 3 feet on the 16 feet stretch.

The house has 40 years and the chimney as been use a lot. Theres not a lot of info on the internet about the maximum "flat or near flat" surface a chimney could have before it goes up. Thank you

On 2018-02-07 by Rodney Lowe

How far from the power source should a class A chimney be ?

On 2018-01-20 by Ron

I have a chimney that is about 2ft below the peak and about 8 feet to the peak. I do not get a good draft. I have a terra-cotta liner in the chimney. Should I extend the chimney or have a Stainless Steel liner installed to correct this problem? Thank you in advance for your assistance..

On 2018-01-08 22:49:40.367110 by (mod) -

I'm doubtful, Trevor, because of fire clearance, protection from vehicle impact, and presence of an open flame or spark too close to the garage floor. Check first with your local building department about what they will allow.

On 2018-01-08 22:28:48.896626 by Trevor

I have a two story home (32by52) with attached garage (30by16). Can I put wood stove in far corner of garage, which means chimney will be roughly 14 feet from second level of my home, and if so, do I need to extend top of chimney above roof of home or will I be safe the 10 foot rule plus 2 from the roof of my garage.

On 2018-01-08 by Stacey

My building uses a gas boiler and hot water baseboards for heating. We have a chimney that ends half way the height of the building on the side of the building (not on top). The chimney is constantly blowing white smoke which enters through my daughter's room window.

My question is what is in that white smoke and is it harmful to the health (gas boiler/baseboard water type of heating system).

On 2017-12-21 by Ron

How high does a chimney and how far from a parapet t on a flat roof

On 2017-12-04 by (mod) - Can I use existing chimney to use flue and then use external flue to exit chimney just under roof eaves.


It might be possible to use part of an existing masonry chimney that then exits to an approved listed metal chimney flue that then intern precedes to the correct height above your rooftop.

However that's a hybrid design that I would not consider without a thorough inspection by a certified chimney sweep or licensed installer. It's important because making a mistake could result in this building fire.

Whenever you use a hybrid or jury-rigged design there are risks that because someone has to invent the connections there will be future problems such as leaks where the metal flue exits the chimney at the building exterior or difficulty in cleaning the chimney because of its multiple bends and turns.

Those in turn mean higher maintenance cost at higher risk of safety hazards.

On 2017-12-04 1 by Doreen

Chimney has been capped. Too expensive to rebuild so will need to do external flue for woodburner.

Can I use existing chimney to use flue and then use external flue to exit chimney just under roof eaves. This is on gable end of hip roof and ridge is more than 3 metres away from where I would exit the new flue. How high must the new flue be above the exit point?

On 2017-11-03 by Mike Florindi

The basement wood stove shares the enclosed plenum behind the living

room non-vented LP Fireplace. Next week we are have the roof

replaced. The area where the existing stove chimney exists also has

to have the wood replaced.

I'll be to replacing the non-vented fireplace in the future. While

the roof is getting replaced - I'd like to prep it so the new vented

fireplace chimney is done.

Question: Until I can decide on a B-Vent or Direct Vent Fireplace -

can I install a second wood stove chimney to be covered either way?

Or is there another way to cover either future installation? How far apart do they have to be. The existing wood stove chimney is inches behind the gas fireplace and curves up top to fit through the roof - stopping me from going stright up from the future fireplace.

On 2017-10-24 16:37:02.370778 by Fred

Is there a clearance requirement for fireplace chimneys and roof vents for the attic? The vents in use are turbines. Thank you.

On 2017-10-23 21:27:00.038949 by (mod) -

Thanks for the critique, Visitor, I'll review the text.

Take a look at the page top illustration: as that should be pretty basic and clear.

If you have a specific question or can point me to something that's particularly confusing in the text I'll be pleased to clarify that.

On 2017-10-23 20:24:08.000679 by A Visitor

Your description of the 2', 3' and 10' clearances is EXTREMELY confused.

On 2017-10-05 14:24:57.618900 by Les Lenchner

What is the minimum height of a boiler, furnace, or any heating device in relationship to the horzontal portion from the outlet?

How much higher must the vertical portion of a chimney be to compensate for a horizontal, 16" pipe that travels 11.25 feet?

On 2017-09-25 by (mod) - Pellet Stove Vent Pipe Clearance Distances, NFPA211(2006ed.) Section10.4Termination:10.4.5

Wayne, I don't understand all of the words in your query ("a past the code") but generally a pellet stove would

1. comply with wood stove venting requirements

2. follow clearances specified for its vent as in the installation manual for the stove

Some of those installation guides will add an additional 12" to an existing chimney top "... to be sure the termination is an adequate distance above the roofline." (Dura Vent Pellet Vent Pro Installation Instructions )

Note also that direct-venting pellet stoves will have different clearance requirements from those venting through a new or an existing chimney.

So if you tell me the brand and model of your specific pellet stove I'll be glad to help track down those specifics.

General reply: 12" above the roof line from the point of penetration.

Some instructions measure on the down-side of the chimney at the roof, but safer is to measure from the higher side of the roof slope. Note that that pellet stove requirement is LESS clearance than would be required for a conventional wood stove or most other fuel burning appliances.

Venting through an existing chimney or flue that was already built to code will usually provide safer and higher clearances (see our woodstove clearance notes). But in that case you will also need to be sure that the existing chimney is properly sized and in safe operating condition for the manner of its intended use.

Guidelines for Termination of Pellet Stove Vent Pipe - NFPA211(2006ed.)Section10.4Termination:10.4.5

- Not less than three (3) feet above any forced air inlet located within ten (10) feet.

- Not less than four (4) feet below, four (4) feet horizontally from, or one (1) foot above any door, window or gravity air inlet into any building.

- Not less than two (2) feet from an adjacent building, and not less than seven (7) feet above grade where located adjacent to public walkways.

The exhaust exit shall be arranged so that the flue gases are not directed so that it will affect people, overheat combustible structures, or enter buildings.

Forced draft systems and all parts of induced draft systems under positive pressure during operation shall be installed gastight or to prevent leakage of combustion products into a building.

Through-the-wall vents shall not terminate over public walkways, or where condensate or vapor could create hazards or a nuisance.

Be sure to follow local codes and all manufacturer’s instructions (including exhaust pipe).

Consult a professional installer and/or call Technical Support for the brand and model of your pellet stove if you have any questions.

On 2017-09-25 by Wayne

What is the code to run a 3-inch insulated pipe a past the code of a roof for a pellet stove

On 2017-09-04 by Todd rader

Have a gas furnace, what are the code requirement for hright

On 2017-08-11 by (mod) - separation between metal chimneys

Metal flue separation distances (C) Carson Dunlop Associates & InspectApedia.comThanks for asking, Dan.

The recommended clearance distances between insulated individual metal flues such as Metalbestos products are discussed briefly at


There you'll see this illustration recommending at least 16" of separation to avoid damage.

Keep in mind that the final authority is your local building code compliance inspector - in most jurisdictions you're required to obtain a permit and safety inspections to install a wood-fueled heater, and those in turn add what amounts to a valuable and free fire safety inspection that I recommend.

Also see what your chimney manufacturer specifies.

On 2017-08-11 by Dan at RockyPoint

I am installing a wood heating stove and a wood cook stove. The flues will terminate 2 feet above the ridge line.

Each appliance will have it's own flue. What is the distance between the flues required I am using Metalbestos 6" flue. And what should be the difference between the tops of the flue. I understand they cannot be the same length.

On 2017-08-10 by (mod) - How high does a flue need to be if there is a terrace on the roof?

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

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 COPIES of BUILDING CODES ONLINE

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) above grade.

3. 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-inch (230 mm) vent termination clearance, and an appliance with an input over 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?


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Or see CHIMNEY HEIGHT & CLEARANCE FAQs - set #1 of questions & answers about chimney height & clearances

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