Chimney height & horizontal clearance distance questions & answers, set #4:

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.

Chimney Height & Clearance Distance Codes Q&A#4

These questions about chimney or flue height & clearance from various building features were posted originally

at CHIMNEY HEIGHT & CLEARANCE CODE

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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

Reply:

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

Reply:

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.

Reply:

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 correct?

Reply:

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.

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?

Reply:

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?

Reply:

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

Daniel

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?

Reply:

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
see
inspectapedia.com/electric/Electrical_Service_Drop.php

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?
Patricia

Reply:

Patricia,

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

• Make sure the damper is fully opened and that the chimney is not blocked and not damaged - hire a certified chimney sweep to inspect the flue for safety and to clean it if necessary.
• Light some newspaper placed at the back of the logs in the fireplace to help establish draft when you're first getting your fire going
• Make sure the ash pit door for your fireplace is closed = if the ash pit door is open air entering at that location will reduce draft seen in the fireplace. There may be ash pit doors both in the floor of the fireplace and also in the basement below the fireplace.
• Be sure that the chimney cap is properly installed and is the right type - a bad or missing chimney cap can cause bad draft as well as allowing downdrafts.
• Open a window or door near the fireplace so that there is plenty of good air flow into the room when you are lighting the fire - you can close this opening again once the fire is established.
• Best practice: after correcting chimney height, making sure the chimney flue is sound and not blocked or dirty, provide outside combustion air for your fireplace

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

Reply:

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 between the upper chimney extension and the roof surface.

See BRACING for METAL CHIMNEYS.

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?

Reply:

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

Reply:

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: 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

Reply:

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:

• The chimney top must be two feet above the ridge of the roof (If the chimney is at or very close to the ridge)
• The chimney top must be three feet (or more) above the roof surface (measured right next to the chimney, at the up-slope side of the chimney - see our sketch above)
• The chimney top must be high enough above the roof surface such that a horizontal (level) line drawn from the chimney top to the nearest roof surface will run ten feet or more before that line touches the nearest (up-slope) roof surface.

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

Reply:

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

Dom,

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

Reply:

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

Reply:

Roman,

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

Reply:

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

Reply:

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

Reply:

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

Reply:

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

FLUE SIZE SPECIFICATIONS

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?

Reply:

Tony,

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?

Follow-up:

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.
Bazzer

(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).

Reply:

Tony

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.

Commen:

(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.

Reply:

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 ARTICLE INDEX to RELATED ARTICLES that includes a live link - ) for articles about wood stove safety.

 

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

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• CHIMNEY CODES & STANDARDS
• CHIMNEY HEIGHT & CLEARANCE CODE

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