Photograph of a too short masonry chimney. Chimney Height & Clearance Questions & Answers
FAQs about chimney height & clearance

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Chimney height & horizontal clearance specification questions & answers:

These questions & answers help clarify the required height or other clearance distances for chimneys.

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.

Green links show where you are. © Copyright 2017, All Rights Reserved.

FAQs About Outdoor Chimney Height & Clearance Codes & Specifications

Adjacent metal flue heights should vary (C) Carson Dunlop AssociatesThese questions about chimney or flue height & clearance from various building features were posted originally at CHIMNEY HEIGHT & CLEARANCE CODE

[Click to enlarge any image]

Question: minimum height clearance for stove pipe on flat roof in front of windows

(Oct 2, 2012) Paula Moss said:

what is the minimum height clearance needed for a wood burning stove pipe when exiting a flat roof. the roof is in front of two 1st floor windows



The minimum chimney heights above roof are in the article above. For the case you describe, there are other distances like from windows, and depending on the total chimney height, even meeting the above-roof minimum distance (3 ft. on a flat roof) may not be tall enough.

Question: remove old brick chimney & send metal pipe out through roof

(Oct 19, 2012) Chris said:

can i remove an old brick chimney below the roof line and just send some sort of pipe out of the roof instead? if so, what type of pipe would you recomend and how would i seal such pipe to the remaining chimney stack below the roof? also this chimney is being used to vent a hot water tank and a gas furnace. any advice will be greatly appreciated


Yes but you'll need to repair roof deck, properly flash the new chimney, extend and connect the new metal chimney down the old flue to the appliance at the chimney bottom or thimble or entry point.

It may make more sense to call a chimney re-lining contractor.

Question: vent a direct vent natural gas fireplace between a door & window?

(Dec 16, 2012) james said:

can you direct vent a natural gas fireplace between a door and a window on exterior wall


Yes if you meet combustible learances, roof clearances,and use proper katerials

Question: metal chimney above rooftop deck

(Jan 1, 2013) James P said:

We just bought a house with a 12x12 ft rooftop deck. The metal stack from the wood burning furnace in the middle of the house extends a few feet laterally from one corner of the deck goes up about 12 feet above the deck.

Can we trim down the stack to lower height or do we have to clear the deck by 10 feet vertically? The total chimney height is over 40 feet to the top of the house.


I would not cut the chimney top height - stay in compliance.

Question: what about chimney clearances to a metal-covered roof?

(Feb 6, 2014) alan said:

I am wondering if it makes any difference to have a metal roof with the wood stove chimney clearences as i have a 12/12 pitch roof so if i have to fallow the guidelines that wold mean if i come out low on the roof i would need at least 10' of chimney outside, is this corect??


Alan you'd think so, right as the metal roof is more fire resistant, but I have not seen an exception based on roof covering type. I understand the issue - on steep roofs the clearance height is quite tall. From what I have read you'll need to go up and probably install a brace. I SPECULATE that the reasoning is that over the life of a building the code writers didn't want to assume what covering was on the roof.

Second, roof height and shape may also affect chimney draft.

Question: clearance of chimney vent from HVAC air intake

(Mar 28, 2014) Angela Giboney said:

How far away should an HVAC air intake be located from a chimney to prevent sucking in the smoky air?


Angela you may have to give more detail for me to make sense of this. A chimney has to terminate above the rooftop with the clearances shown in the article above. I'm unclear how an HVAC air intake would be located nearer a chimney termination than would be the roof surface itself (on a sloped roof) or a nearby window, wall, etc. as discussed above.

Question: confused about the ten foot three foot rule

(Apr 25, 2014) Anonymous said:

How can the top of the flue be ten feet away from any roof surface and only three feet above the roof surface at the same time? (Points one and two above) It is important not to say things that can be understood, but to say them so they cannot be misunderstood. Isn't English fun!If the house was built 40 years ago and the top of the flue is only eight feet away from the horizontal distance to the top of the roof, does one have to tear the house down?


Thank you for the comment, anon. I will review the text for clarity. Meanwhile, take a look at the sketch and arrows in the article above under the heading

Required Chimney Height Above Roof Surfaces or Ridges

You will see that the ten foot rule is a horizontal distance and the 3 foot rule is a vertical distance. Those measurements become easier to understand when viewing a sketch of a chimney at a sloped roof surface.

I'd welcome any specific text wording that you suggest in clarification


Question: clearance between chimney and electrical wires

(May 18, 2014) Anonymous said:

How far does a woodburning stove chimney stack need to be away from the wires outside that connect to the house?


Interesting question. The answer is in my OPINION it should

- meet the clearances from combustibles required for that chimney type to avoid risk of heat damage to wiring

- meet the clearances from building components required for overhead electrical wiring

Question: Chimney on main level fills basement with smoke

(May 19, 2014) Anonymous said:

I have a triple flue chimney (fireplace on main level, fireplace in basement, and oil furnace) I have been having problems since moving in and having the chimney replaced.

When we light the upstairs fireplace, the basement room where the basement fireplace is fills with smoke.

The person who built our chimney has put a rain cap on the upstairs flue and an extension on the basement flue, however this has still not solved our problem. The person that build our fireplace has now walked away and said we need to have someone install an air exchanger in our home to fix the problem, however that is pretty pricey. Do you have any suggestions for us?

Question: converted wood burning to gas fireplace, where do I vent out?

(May 31, 2014) Anonymous said:

Hi, I have a flip I am working on that was a friend of mine that passed. His fire place was used originally as a fire burning fireplace but was zero ground clearance. I have converted it to be a gas fireplace and was hoping to have the vent and access to go out on the side of the house instead of having a chimney. My contractor is telling me he was told that we have to have the access go out the roof due to the fireplace is an open fireplace instead of glass front.

My question is if we want to keep it with an open feel what options do I have and if it has to have a chimney how high does the flute need to be and what size would the flute be?
Thank you for your help! If I have to have a glass front does that mean I have to replace the entire fireplace box or can I have just the glass installed to then be able to go out the side with a vent system?



I'd sure like to help with this but frankly with no details and no on-site access I'm chicken to offer much specific advice about an open-faced gas fired fireplace. The risk is that you do something wrong and spill fatal carbon monoxide into the building.

I don't think you're likely to have to replace the whole fireplace box or chimney.

The best approach would be to start with a call to the manufacturer of the gas unit you want to install. Describe the installation location and ask their advice on making a safe working fireplace.
Of course there will be specifications that came with the new gas fireplace that must be observed for safety and function, but as your installation may be a bit different, it's worth a call to the manufacturer.

Question: how to diagnose a smoky fireplace & chimney

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

Reply: "Why would my fireplace smoke up the house during the time I have a fire. It's a masonry chimney."

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

RE: "my chimney is not 2 foot higher than the peek of the roof."

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.

Question: Do we have to comply with chimney height clearance requirements for a 12/12 pitch roof? Does a power-vent flue excuse chimney height requirements?

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.

Question: We're adding a roof whose ridge will abut the existing chimney. How does that affect chimney height clearance requirements?

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).

Question: can I fix my own chimney?

I just had a home inspection done and the inspector said that my furnace pipe that goes 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. You could get a bid from a chi net person who is certified.

Question: We had a chimney fire and a WETT inspection

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.

Question: my chimney extends 2 ft not 3 ft up above the roof surface. Does it comply?

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 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.

Question: Can I put in my own chimney using a single wall and triple wall?

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 triple 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.

Question: smoky fireplace on first lighting a fire

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

Reply: how to improve fireplace draft on initial ignition of a fire


There are plenty of reasons for backdrafting when first lighting a fire, including a chimney that is blocked, too short, has an open cleanout door, and more. Here are some things to check in order to improve fireplace draft when first lighting a fire:

  1. Watch out: Have your chimney checked for safety and blockage and it's clear, and have the chimney cleaned of creosote and soot; depending on the amount of usage and type of fuel burned in a fireplace, chimney cleaning may need to be performed more or less often than annually.
  2. If your fireplace and chimney are older and do not include an outdoor combustion air supply, then try opening a nearby window or door to assure very good air supply and no negative air pressure when first lighting the fireplace. Once the fire is going well you should be able to close the window or door; of course this will draw some cool air into the house and result in a net heat loss, but, then, operating a conventional fireplace (without glass doors or other features) will pretty much always result in a net heat loss to the building.
  3. Because the fireplace chimney and air in the chimney are cold when you first light a fire in a fireplace, the initial warm smoky air can face inadequate draft - it has trouble pushing up that column of cold air. You can improve the initial draft by lighting some newspaper placed at the back of the fireplace.

Question: how do I find sizes and dimensions for a fireplace box?

Is there somewhere I can find standard fire box sizes for a masonry fireplace? - Lou 4/25/2012


Lou - certainly - just search InspectApedia for "fireplace dimensions" and you'll find the article. Or go directly to FIREPLACES & HEARTHS

Question: Can I vent a gas fireplace into a masonry chimney in bad shape?

I would like to vent gas fireplace insert into masonry chimney. The chimney is in bad shape, but the portion 3 ft above the rooftop is good. Will venting to 3 ft height be sufficient with appropriate manufacturers specified metal liner? Do I need to concern myself with lateral 10 ft dimensions? - Roman, 5/27/12



Usually if a chimney is structurally sound it is relined or a liner is run up thorough it. For a gas fireplace that'd be a B-vent of sufficient diameter. In fact, a chimney that is too large in diameter for the appliance it vents may never work properly as a small appliance can't heat the chimney enough to establish a good draft;

If you line the entire chimney to the top, and better, use an insulated liner or insulate around the liner, the design should work.

And yes you still need to apply proper chimney clearance rules for gas vented appliances or B-vents.

Watch out: DO NOT just terminate a vent up inside the chimney - you're asking for dangerous carbon monoxide hazards and other problems. The height of the chimney above the roof surface depends on where it exits - and is shown, explained, and illustrated ad nauseam in the article above.

Question: outdoor wood fired oven with a metal flue and a canopy

Building an outdoor wood-fired oven that will have a metal flue. Plan on a permanent canopy in front of it with a metal roof. Roof of oven will be hardiboard (cement product). What kind of clearance will I need between the roof of the flue-top and the oven. Between the flue-top and the roof of the canopy? - Frank, 7/7/2012


See the chimney clearance specifications above as a starting point, but because your oven (of unspecified use) may be in service for long periods or at unusual temperatures, it makes sense to also check with your local fire inspector.

Question: outdoor wood fired boiler chimney clearance to building - ending below roof

With a 2 story walkout basement can I put an outdoor wood boiler with the chimney 10'+ from the wall/gutter even though the top of the chimney would not reach the roofline? - John Henry, 7/23/12


I'm doubtful, John; a chimney ending below the roof line of a two story house may meet the ten-foot distance rule correctly, but I suspect that in at least some conditions you'll be blowing smoke at nearby windows and walls.

Question: three adjacent chimneys

I came across a house today that has three chimneys right next to each other. The first two is a wood burning fireplace and the second is for three gas appliances: a boiler, water heater and a gas free standing stove. Just above these two chimneys is a steel plate and above the plate is a third chimney for a free standing wood stove. I know its wrong in so many ways but can't fine a reference. - Kelly Moore 8/27/12


Kelly, send us some photos or sketches and we might have a clear enough understanding of the situation you describe to offer some comment.

Question: installing a wood stove through a one story roof

Greetings; I am considering installing a wood stove on the back end of a single story kitchen addition which has a low pitch roof. The kitchen addition is about.18 feet away from where it joins on to a story and a half main part of the house. The second story has one window about 18'. away from the proposed stove pipe which will be a Selkirk.SS type. Question: How far does the chimney need to be from the second story portion of the house to be safe from sparks and smoke? Thanks- from someone who does not want to freeze another winter because he cannot afford oil. QC - Rev. Quincy Collins, 9/2/12


Rev. Collins,

The answer is in the text above - the same rule for structures applies as for adjacent roof surfaces. See "Roof Clearances for Chimneys 10 Ft. or more distant from the Ridge"

Question: Large masonry flue, extension fell off, reduced use, draft worries

We live in a smaller 3 flat with an oversized chimney (used to exhaust a boiler) opening directly adjacent to a much taller mid-rise. Until recently, there was a metal extension terminating above the taller structure and the chimney now only handles 3 water heaters instead of a boiler. As a section of the extension fall off, we need to do something to avoid back drafts. Do you know if it's legal and safe in Chicago to terminate lower than the mid rise's roof line, if we use a properly sized liner in our stack and install a draft inducer? There are no windows that would be affected. James. - 5/1/3013

Reply: dealing with a reduction in use of a large masonry flue

There are general chimney height rules that we document in the article above and that we also discuss at


But at any specific site there can be nearby structures that, even if they meet the distance requirements, interfere with draft or cause a downdraft.

When you vent just a few small heating appliances into a large chimney there is a good chance draft will be inadequate and thus the systems unsafe ( a potentially fatal CO poisoning hazard).

I can't say what's legal (vs. safe) for your specific chimney just from your email, but the fact that you describe a chimney part as having fallen off is itself a concern and an indication that the chimneys and flues need inspection and repair by an expert. Indeed you may need to line the flue or install a draft inducer.

You could check for backdrafting just at the water heaters, but an individual test is not reliable as site conditions vary. For example draft will be different at different outdoor and chimney temperatures and will vary depending on how many heaters are running, indoor combustion air supply, and other variables.

Question: Short chimney, moisture problems in attic

(Feb 8, 2012) Tony said:

I have severe condensation and mold forming on one section of the underside of my attic roof. Last year I pulled back all insulation from around the edges of the roof to ensure that air could circulate and additionally had a number of vent tiles installed thinking that this would eliminate the problem.

I have noticed that steam from my old central heating boiler frequently collects under the eaves at this section of the roof (the heating is on constantly during the day), and additionally this area almost directly above a small shower room which isn't ventilated.

We do open the window when using the shower, and typically the shower is only used for a maximum of 30 minutes per day (however we do still get a bit of mold forming above the window).

The problem seems confined to this section of the attic, and we don't have problems such as significant condensation on windows in the house which may indicate abnormally high moisture.

There is nothing else located at this section of the attic; it's not directly above the attic hatch, and is away from the central heating header tanks (which are cold anyway).
The house is typical 1990 UK construction.

Do you have any thoughts as to whether either the shower room or the central heating boiler could be the likely cause of the condensation, or whether I've missed something?



Let's start by asking why we have steam from your heating system entering the attic - or more likely, moisture from condensing steam vapor. Perhaps there is a steam vent that is remaining open too long after the radiators below this attic section are warm?


The steam I'm referring to is from the flue from the boiler. It exhausts externally at just over 2m height, but unless there is a good breeze tends to rise straight up and billow around under the eaves of the roof (two storey house) where there are a number of vent bricks for the roof space (which I sealed up just at this location actually).

I think this is almost exactly the same location where the condensation is forming on the underside of the roof.
I don't know for sure that this moisture is entering the attic space, but on cold still days with the boiler working overtime there seems to be a lot steam knocking around under the eaves.

(Feb 10, 2012) BarryFulbrook said:

sounds like a condesing boiler Like I have, verry eficient but has a constant plume of steam comming out the exhaust, You need to duct this away from the side into a flue so it dosen't go in the eaves or you can expect trouble later.

(Feb 10, 2012) Tony said:

It's actually an old non-condensing boiler. You've got me thinking now that there might be something wrong with the boiler itself. I assumed that it was normal to have a visible plume from a non-condensing boiler in cold weather, but possibly not to the extent I'm seeing (ie chuffing away like a steam train).



Though flue gases and combustion products might produce a visible plume it should not be "water" or steam. We would not expect to find any significant levels of steam (water, water vapor) in the exhaust flue of any kind of boiler. If it really is water/steam, then your if your boiler is a steam boiler it may be damaged, sending steam up the flue instead of up the steam pipes.

If your boiler is a "hot water" or hydronic boiler (not steam) it is normally full of water under pressure (say 25 psi when hot), but could also have a leak that boils water away and leaks into the flue.

You need a service call to

- check for proper burner operation (should not be smoking)
- check the boiler for damage - remove the jackets and inspect

Let us know what you find (and let us know more accurately what kind of boiler you have, hot water or steam, brand, model) - it may allow further comment and will help other readers.

Follow-up:  (Feb 19, 2012) Tony said:

It's a hot water boiler - Ideal Elan II, about 22 years old. I'm pretty sure it operates on static head from a water tank in the attic. Sound advice to get it checked out. I'll let you know what I find. Thanks very much.


(Sept 6, 2011) Bret said:

Thank you. Your page has helped me a lot. Its my first time with a wood stove and your diagrams and explanations were very helpful.


Thanks for the nice note, Bret, we work hard to make our information detailed and unbiased and useful. We would welcome any questions or comments that you may have.

Also be sure to see "Wood Burning Heaters Fireplaces Stoves" (Article link: on this page Continue reading provides an INDEX to RELATED ARTICLES that includes a live link - ) for articles about wood stove safety.

Question: neighbor complaint about smoke from chimney

(July 2, 2014) Alexandra said:

Hi, our neighbours are exceptionally sensitive about any smoke which comes from our heat master firebox- installed in a brand new house 7 yrs ago, to council specs and just recently cleaned.

We wondered if extending the metal flue above the current height would help alleviated any smoke from their backyard, which sits diagonally adjacent to our house and below the chimney by at least 20 feet. We would do anything to avoid the aggression we incur every time we light a fire in the day!( not the evening) The council have checked the fire and it conforms to all regulations.



I read your query last night and then spent some time thinking about it as I don't see a cheap easy answer. Are you in the U.K. ? We've had a spate of requests around this topic, mostly from our U.K. readers of late.

A fireplace and chimney that meet standards and regulations for your country and city can still perform poorly or generate smoke complaints depending on local terrain or building features that cause poor draft or annoying smoke distribution patterns.

I would

- build a fire that generates visible smoke
- step outdoors and observe very carefully where smoke travels
- examine the building and terrain features as well as obtain data on prevailing wind directions in order to better understand downdrafts and directions of air movement

Discuss with a chimney expert:

- whether or not the chimney is drafting properly

- whether or not the chimney cap is the optimum design

- a concern for the effect of site features, terrain, wind on smoke distribution

- whether or not an extension of chimney height can possibly improve the situation (without having to go to a ridiculous or unsafe height), and the requirement for additional bracing if the chimney is extended

- choices of fuel that may reduce smoke output

- testing and confirmation of adequate combustion air

So that other readers can comment I'll also include this discussion in the FAQs above.

Do keep me posted and add additional information if you can - as the discussion will also assist others.

Question: change chiney from round to square flat

(July 24, 2014) Nicolas said:

I would like to change the chimney stack in the wall from 6" round to a square , flat version, so I will have more room in my bathroom!
Thank you.


Watch out: changing a round chimney to a "flat" rectangular shape, even if it is the same total number of square inches, may severely restrict the chimney draft, making the chimney unsafe. You will need to consult a chimney expert to determine how much venting area is needed.

Question: don't like the ten foot chimney clearance rule

(Sept 9, 2014) Dave p. said:

I'm installing new trusses and changing the slope of the roof in my house, the chimney wont meet code with the new roof design. I submitted the plans to the building inspector and there was no mention of changing the chimney when the plans were approved.

I have all the permits to complete the project however does the inspector have the power to make me increase the chimney height even though there are no modifications to the chimney planned or permit requested for the work? The chimney protrudes from the roof over three feet however doesnt meet the 10' rule.

I would have to extend the chimney another six and a half feet to comply and it would look horrible as it is attached to the front of the house and exposed to view from the street. Thanks for any advice or help you can give.



The local building code compliance inspector has final legal authority over building permits and approvals and assertions of code compliance. More, if s/he does not approve of your chimney installation most likely it's a legitimate safety concern as well.

But there might be a misunderstanding of chimney height requirements involved. If you can show an authoritative source or can obtain a sign off from a local licensed design professional such as a licensed engineer or architect your local inspector may accept that alternative design.

My own preference is to meet the roof and chimney fire safety guidelines regardless. If it's a choice between aesthetics and burning down the new roof and house ... well enough said.

Question: chimney shared between two buildings: gas vs oil fired appliances

9/19/2014 Anonymous said:

I am a plumbing contractor and a month ego i installed a gas boiler and a gas water heater.When i wanted to connect the smoke pipe to chimney i found out that the house adjacent to the house i was working,was using the same chimney.One chimney for two houses.Is this common? The old heaters were oil fired boilers.Converting to natural gas boilers who has the right to use the chimney,since the combustion is atmospheric ?

Reply: shared flue may be unsafe

Wow Anon, that gives a new meaning to "shared flue" and creates obvious problems and, I'd expect surely violates local and state or provincial building codes. There are obvious safety and control issues incuding:

- fuel conversion normally would require a flue inspection, cleaning, possibly even modification, but since the flue continues to be used by an oil fired heater in a separate building control is just about impossible.

- Draft regulation is up in the air

- Where some jurisdictions do permit gas appliance venting into a flue that also vents an oil fired appliance there are flue entry guidelines to minimize the risk of backdrafting.

I'd give this problem to the owner with a red tag on the heating system noting that there are code, legal and safety issues that can best be resolved by determining first whose chimney it is.

Question: chimney shared between two houses - gas fired heaters

(Sept 17, 2014) Anonymous said:
I am a plumbing contractor and a month ego i installed a gas boiler and a gas water heater.When i wanted to connect the smoke pipe to chimney i found out that the house adjacent to the house i was working,was using the same chimney.One chimney for two houses.Is this common? The old heaters were oil fired boilers.

Converting to natural gas boilers who has the right to use the chimney,since the combustion is atmospheric ?


ocal and state or provincial building codes. There are obvious safety and control issues incuding:

- fuel conversion normally would require a flue inspection, cleaning, possibly even modification, but since the flue continues to be used by an oil fired heater in a separate building control is just about impossible.

- Draft regulation is up in the air

- Where some jurisdictions do permit gas appliance venting into a flue that also vents an oil fired appliance there are flue entry guidelines to minimize the risk of backdrafting.

I'd give this problem to the owner with a red tag on the heating system noting that there are code, legal and safety issues that can best be resolved by determining first whose chimney it is.

Question: wood stove chimney outlet height vs surrounding properties

(Oct 6, 2014) Anonymous said:
I have a single storey flat roof extension on the rear of my 2 storey semi detached house, into which I wish to install a wood burning stove. Would the outlet pipe need to be above the main roofline of mine and surrounding properties.

(Nov 8, 2014) Anonymous said:
can a wood burning stove flue be installed on a single storey extension if so how high does the flue outlet have to be?



Check the sketches in the article above. The 10 foot rule explains the clearance you need: both above the flat roof and 2 feet above the point at which a horizontal line from the chimney would touch the highest portion of the nearest roof.

Anon the chimney outlet needs to not only be proper height above the roof surface but proper distance from any opening that could take flue exhaust into the building. Details are given above using windows as an example.

Anonymous: if the chimney top is two feet above the ridge and assuming you're referring to gable end vents located in a roof end wall that is below the level of the same roof top the chimney should be in compliance.

Question: when measuring the chimney flue clearance to the adjancent structure, do I measure to the wall or would I measure to the edge of the overhang?


I am wanting to put in a fireplace on my covered patio. The patio roof is only one story tall and attached to the house which is 2 story. When measuring from the flue to the adjacent building, I'm very close to the 10ft rule. My question is, when measuring the flue to the adjancent structure, do I measure to the wall or would I measure to the edge of the overhang?

(Oct 23, 2014) Drew said:
I own a building in massachusetts that dates back to the early 1900's. After my building was built an adjoining building was erected and they subsequently had to raise my chimney to comply with code requirements since their building was 4 stories taller.

There's been a maintenance responsibility issue of late and I was under the assumption that my neighbor was required to maintain the chimney since they raised/extended it. I know New York law specifically cites this, section 27-860 adjoining chimney, but was curious if massachusetts has a similar code that you could provide me with.

(Oct 27, 2014) Anonymous said:
The brick chimney is adjacent to the gable vent. The gable vent is in the center of the wall.

The chimney is capped with openings about two feet above the roof line on the same side as the gable vent. I am worried that carbon monoxide from the chimney may be drawn into the gable vent. Is the chimney in compliance with Southern Building Code if it vents two feet above roofline even though it is also about two feet away from the gable vent? Thank you for your kind assistance.

Question: backdrafting from wood fireplace

(Nov 11, 2014) mohammad said:
I get backfire insde my house coming from my wooden fireplace


Mohammed what you describe is potentially dangerous. I would stop hpusing the chimney and ask for an inspection of the chimney for blockage, leaks, proper cap, and general safety. Let us know what you are told.


Question: Can we put a stovepipe through a window

(Nov 15, 2014) Ben said:
Can we put a stovepipe through a window

Reply: no

For ANY building wall penetrastion of a "stovepipe" - you don't say what fuel, fire clearances, etc - you need to be sure to respect fire clearances from combustibles, including whatever is being used to seal the window opening, outside on the building wall, chimney height, etc. In most jurisdictions you also need a building permit and appropriate safety inspections.

So "can" - meaning physically able, yes. "Safe" is another question.

Question: build stone around gas B-vent chimney

(Dec 4, 2014) Stacy said:
I have a b-type vent for a gas fireplace coming out my roof and I want to have a better look to it by putting stone around it. Are there rules about what material should frame around it to have stone to make it look 'pretty'?


Smart question Stacey.

If you can tell me the brand and other information stamped into your B-vent we can dig out the manufacturer's exact specifications on and rules about enclosing the vent with a chimney chase - air space, air circulation, fire clearances.


Question: height for outdoor furnace

(Dec 9, 2014) Anonymous said:
What is the correct height for an outdoor furnace and how close to property lines can the furnace be


Anon presuming you mean a chimney venting a furnace - of some unspecified fuel - the heights are given in the article above. Let me know if any of that is unclear. Thanks - Ed.

Question: extending a short chimney over a bungalow

(Jan 15, 2015) Gary S said:
I have a bungalow and my chimney is very short and is no way near the top of the roof. If i was to make this 2ft above the roof line this will make my chimney very tall.....will this also make it unstable in windy conditions?


Gary stability questions depend on the chimney materials and type of construction; two feet above a roof line is not usually enough to find wind damage but if the whole chimney free-height is substantial indeed you may need to add bracing.

Be sure you understand the height drawings accurately before extending the chimney height.


Question: making a hole in a B-vent for gas testing

29 January 2015 Anonymous said:
Is there an acceptable method of penetrating / sealing a double wall (B-vent) for CO testing?


For B-vent chimneys and gas fired heaters I would NOT recommend making a hole in a B-vent and I'm surprised that it seems necessary. Why not measure flue gases readily accessible via the draft hood or at the chimney top? Measure instead at the heating appliance, chimney entry point, or chimney top.

Conversely, for *oil* fired heating appliances it's common practice to drill 1 or even 2 small diameter holes in the flue vent connector at the breech to permit insertion of a smoke tester and a CO2 measuring device or other gas testing instrument.

See DRAFT MEASUREMENT, CHIMNEYS & FLUESfor photos of this flue testing opening


(Mar 18, 2015) r kilts said:
whats the best way to cut down a too tall chimney that,s hard and dangerous to get to.



I see contractors either erect scaffolding or use a bucket truck. Watch out: dropping chimney components by an inexperienced contractor or worker could kill someone.

Question: What height does that exhaust have to be away from the deck surfac

(May 17, 2015) Derek said:
I have a roof top deck that has a chimney top located next to it. the Brick and mortar stop at about 4' high from deck surface and then a arrestor is about 18" tall.

What height does that exhaust have to be away from the deck surface, and do I need to turn vent at a 90 deg away from deck.

Imagine you walkout on to a rooftop deck and on the side of the house there is a chimney across the deck where the handrail stops on one side and continues on the other. The clearance from structure is about 15' ( the span of the deck) Can I just add a metal chimney stack and if so, what height from deck surface does exhaust need to be. I have read a lot of things and the answer is varying. So I'm now asking it directly thank you



please lighten our workload by asking questions in just one place. Thanks.



(6 days ago) Nassrine Niemi-Farhoody said:

I posted this question on another section of this website, but not sure where it is - I am re-posting the question here - my mother's neighbor built a building next to hers that is one story taller - there is no separation/space between the buildings and the taller building dwarfs her chimney (it vents the heating system and hot water heater) - what can she do to correct the lack of air flow? I have a picture that shows the extent of the problem. Thanks.



Question: am I required to raise a too-short chimney when selling my house?

(Aug 14, 2015) Patricia said:
i am selling a 40-year-old home in New Jersey. The home has the original fireplace and chimney. The buyer's home inspector states that the chimney height does not meet code. Am I required to raise this chimney? We have never had any problems with smoke, etc. Also, there was no mention of any code violations 12 years Go when I purchased this house.



Watch out: Our first worry as a home owner, seller, occupant, or remote opinionater is that we should try not to kill anybody. So if a chimney is unsafe, your first concern as a home seller should be your safety and the safety of people who come after you in the home. You want to be certain that the buyer / future occupants, are aware of any safety hazards that you know about. That's a separate question from who pays for what when buying or selling a home.

ONLY the local building code official can properly and legally declare that a building component "does not meet code" as he or she is the final legal local authority.

However a home inspector, speaking somewhat generally, might opine that she or he would expect a local code inspector to call out a component as "not meeting code" based on what the inspector knows about building codes.

My opinion is that code citations are a shortcut to be avoided, not only because of lack of legal authority, but because there can be plenty of hazards at a building that could kill someone or be very expensive to repair but that would never be identified as a "code violation".

In your specific case, I'd want to know what the inspector actually saw - it would be a more useful as well as more professional inspection report if it contained specifics rather than a shortcut statement. If we were to *guess* that the inspector thinks the chimney lacks proper clearance above the roof (as you can see in the article above) that's an important call to make not so much because it could be called out as a violation by the local inspector as because it is unsafe: a too-short chimney increases the risk of a house fire.

The questions of draft adequacy are separate from the fire risk.

Happily for you the course of action is easy:

Have the chimney inspected by a professional such as a chimney sweep / repair company who is certified by the National Chimney Sweeps guild. If that pro finds any safety hazards regarding the chimney they should be repaired. Typically, extending a chimney top height to improve clearance is not a major expense and will certainly be less than 1/10 of a % of the price of a home in New Jersey.

About what was not noticed when you bought the home, presuming that the chimney has not lost height through damage, the conditions would have been present then even if your inspector didn't mention them - vs current conditions such as a deteriorated flue, blocked flue, creosote-coated flue that need cleaning or repair.

Question: how far must drywall be from a chimney?

(Sept 12, 2015) Wendy said:
Since installing a heat pump and an efficient furnace, only my hot water tank vents through my chimney. Doing some renos and want to know how far must the drywall be from the chimney?I am hoping to gain an inch or 2 in this area.


Wendy: I can't guess, given we don 't know the chimney type, materials, nor fuel being vented. I'm guessing you're discussing a metal chimney of some type. We give fire clearances for metal chimneys of various types at


(Sept 15, 2015) Alice said:
Hello- could you let me know what the specific code (perhaps IBC or IFGC) is for chimney termination as it relates to the proximity of a window? Also, any comment re an overhead trellis that will be directly adjacent to my chimney and the code concerns that may arise from that in relation to ventilation (perhaps NFPA). Many thanks!


please see

Question: chimney height from burner top?

(Oct 7, 2015) Goutam Pramanik said:
Is it possible to place the chimney at a height of 3'6" from the burner top?


I don't understand the question. "Burner top" ? What burner, what fuel, what kind of chimney, what total height, etc. remain questions that need to be answered.

Question: B-vent top near masonry chimney

(Oct 26, 2015) Nick said:
I have a vertical B-Vent from a furnace that terminates a few feet horizontally from a masonry chimney. The B-vent terminates vertically 2' above my roofline, but it is not above the masonry chimney. Does the masonry chimney count as a "vertical wall"? Does this mean that my B-vent is not high enough?


No, in my opinion a masonry chimney should not ocunt as a vertical wall.

Question: chimney for pizza oven on a screened porth

(Dec 22, 2015) Joe S said:
I have a very small pizza oven (terracotta)in a screened in porch with a metal roof, it's well ventilated. The stacks are thru the metal roof (straight up) with a cap. How far does this need to be from the top of the metal roof. I am assuming 3' would be acceptable, hopefully. Thanks, Joe S.


CHIMNEY HEIGHT for Types L & Type B Vents address this

Joe you don't name the fuel; if you are using gas fuel, take a look at the B-vent chimney to roof clearances in the table in the article just above.

(Dec 24, 2015) Joe S said:
Sorry about that. It's a small round (terracotta) wood burning oven just 22" in diameter and generates about 500 degrees(F) perfect for one 12" Pizza. Currently, I have it placed 3' (high) from the bottom of the slanted steel roof to the top of the stack. The screened room is an addition and the portable oven is 15 feet for the house. Another question for which I can't find an answer, is... what is the approximate temperature by the time the smoke gets to the top of the chimney if the temperature inside the oven is approximately 500 degrees and the stacks are about 8 foot from the oven to the top of the pipe/stack (on the roof). I am not too worried about that because here in Arizona that roof can get to well over 100 degrees when that outside temperature is 110 degrees in the summer but still curious to determine the temperature by the time it gets to the top of the pipes/stacks. Merry Christmas and thanks for the help. Joe S.

Mod said

Interesting question, I'll have to research it. The temperature drop vs height will depend on a number if variables including at least

Chimney materials
Outdoor temperature
Wonderful velocity
Temperature of entering flue gas
Gas density
Gas velocity or draft
Cleanliness of the flue
Site specifics
Sun gain

Question: neighbor's chimney too close to our house

(Feb 9, 2016) Stewart said:

Our neighbour has built an external brick chimney stack between his and our house. The original space was 105 cm and is now halved.

The stack faces our gable end which has an air brick and tiled roof air vent facing the stack. Their rainwater gutter which ran parallel to our gable end has been diverted around the stack and now overflows rain water down our gable end wall which bounces off the concrete passage well above our damp proof course.

What to do..I have already mentioned to the builder and owner that this would happen but to no avail.
Your help would be appreciated since we are about to sell.



It is certainly not acceptable for a neighbour to drain their roof onto another building's wall.

If the neighbor won't correct the problem you may get help from your local building department. Use our page bottom CONTACT link to send me some photos that illustrate the situation and we can comment further. Keep me posted.


(Feb 14, 2016) Stewart said:

Many thanks for your assistance.
Council Building Inspector on site in a few days and issued a 14 day remedy notice.
Builder back on site next morning.

Owner suggested that our cavity wall will absorb the gutter overflow without any damage as that was its function and not cause any damp.spector
It had been like that since Xmas and he knew about it all this time but said and did nothing.

A local builder gave the same advice.
What clinched it was I read out your first sentence to the Inspector.
If you would like photos do you have an email address ?

Moderator said:


Stewart: you will find our email at the page bottom or top CONTACT link. I'd be glad to see photos of the situation and I may be able to comment.

I'm not familiar with a good construction practice that deliberately sends water into a cavity wall and I'm doubtful that over the life of a building water can run inside of a building wall without making trouble.

I'd need to understand the construction of your "cavity wall" but if you mean that there is a masonry wall with an air space between the outer brick or stone and the rest of the wall structure, even with good wall-bottom drainage, it would be a poor practice to direct water against the wall.

The wall drainage system is likely to be overwhelmed by water way beyond its design level, and continued water and moisture in the wall invites sending moisture into the interior-side wall components where we risk - various troubles depending on the materials of construction. I'd worry about mold, effloresence, rot, and electrical wiring damage as well as damage to HVAC systems if the walls include ductwork.

Question: Godin Cervalou which needs a 15 cm flue but the fitters couldn't get this dimension down the chimney

(Feb 12, 2016) Sue Wilson said:
We bought a Godin Cervalou which needs a 15 cm flue but the fitters couldn't get this dimension down the chimney. How can we measure the width of the chimney please and can anything be done if it turns out to be 14 cm as suspected?


The chimney interior dimensions are ususally visible through the chimney throat, through a chimney entry thimble in the chimney side, or at the chimney top. You may however need a Chim-Scan camera inspection to find an obstruction or damage that you can't see from these openings. Try first inspecting from the chimney cleanout using a good light and a mirror.

Question: I would like to put a wooden stove heater into my conservatory.

(Mar 10, 2016) Craig said:
I would like to put a wooden stove heater into my conservatory. I believe where I could put the heater would be 10 feet away from the external walls of the house. The house is 3 stories. Does this give me enough clearance, would this be ok. I'd like to try and avoid a 3 storey flue. What are your thoughts?



In most places you need a building permit and fire department inspections to install a woodstove. Those steps will review your local clearances from combustibles. I can't answer a general safety question from a brief e-text as there could certainly be unsafe installation details that could burn down the building.

Question: short chimney in converted log home

(Mar 28, 2016) Anonymous said:
I'm purchasing a converted log home. It has a gas furnace and that chimney looks short, it also has a fireplace that was converted to gas, and the inspector said that chimney was too short as well. Can I use chimney pots to extend the chimneys?


Your local building or fire inspector might accept a chimney pot, depending on its design, materials, and height.


Question: gazebo next to outdoor free-standing fireplace

(Apr 7, 2016) Ernesto said:
I am building a gazebo next to an existing outdoor free standing fireplace. Does the chimney height and distance from the roof of the gazebo require the same code clearances as those for a home? i.e. 2 ft above the highest peak within 10 ft.


I would respect those clearances - after all, Gazebos burn too.

Question: replace masonry chimney that is detroratoring with metal?

(May 10, 2016) Becky said:
Our church has a masonry chimney that is detroratoring and we are wondering if we could replace that with a metal chimney. We have one estimate for repair for almost $13,000 and we were looking at maybe shorting the chimney but that appears to be against code. It is a forced air heating system.



You can usually replace a masonry chimney with a metal one, typically insulated stainless steel; But of course if the old chimney is a hazard it'll need to be removed. Removal is also an expense.

Depending on where the heating furnace is located it may be possible to eliminate the chimney entirely, going to a direct-vent installation. Ask your heating service company about this option.

That may be what you meant by "shorting the chimney" - I'm not sure. Certainly you can't just arbitrarily make a chimney literally "shorter" - without fire, function and other concerns.

Search for DIRECT VENTS / SIDE WALL VENTS to see details of that option.

Question: explaining the ten foot rule for chimney clearance

(May 18, 2016) Dean said:
Just want to be sure that I understand things correctly. If installing a chimney (framed chase to extend up from the roofline) the nearest part/structure of the house must comply with the 10' rule, which in my case would be the outside edge of the overhanging soffit of the higher roof line and not the outside wall of the house below that soffit?


Yep. Clearances address fire safety so IMO we need to include all building components that might be affected. See CHIMNEY HEIGHT & CLEARANCE CODE

Question: neighbor's unsafe pellet stove?

(June 3, 2016) Liz said:
My neighbor has a pellet stove with the chimney coming out the side of the house. The pipe goes up maybe 8 ft and is well below the roof lines! We r starting to see black in our ceilings and I'm thinking its from the smoke from their chimney. They told us that they are within the requirements but that just doesn't make any sense to me! Is there a specific code I could look at to show them that the chimney should be above the roof?


Possibly you're quite right. A chimney that does not terminate above the roof line is not likely to be correct and could be a fire hazard; it also is a clue that a system was installed without the required building permit and safety inspections and approvals.



(July 14, 2016) Andrew said:
O live in a bungalow and my neighbour is building a three storey house eight feet away from my house. It looks like he will have windows that are higher than my chimney - are there any code issues - will I have to extend my chimney height?


Sounds like a local building code and property line set-back problem indeed. I'd check with local building officials; you may want to extend the chimney height.


2016/07/21 Gary said:
We have a mason fire place ( fire brick ) and the installer says do not install a chimney cap. He says it is not required and it affects how the flu works




Continue reading at CHIMNEY HEIGHT & CLEARANCE CODE or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see BUILDING CODE DOWNLOADS - free downloadable PDF files of building codes & standards

Or see CHIMNEY HEIGHT & CLEARANCE CODE FAQS-2 - set #2 of questions & answers about chimney top clearance distances


Suggested citation for this web page

CHIMNEY HEIGHT & CLEARANCE FAQs at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia


Frequently Asked Questions (FAQs)

Click to Show or Hide FAQs

Ask a Question or Search InspectApedia

Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

Comment Box is loading comments...

Technical Reviewers & References

Click to Show or Hide Citations & References

Publisher's Google+ Page by Daniel Friedman