Thread: wood stove chimneys vs. others

Is it possible to tell a chimney from a wood stove from other metal prefab chimneys? I've been trying to find out myself, but no luck.

Similar Threads:

• Fuzzy wood under front porch
• Fireplace Wood to Gas
• Wood Structural Panel Sheathing or Siding Used to Resist Combined Shear & Uplift
• Exposed wood joist in return air
• Wood Burning Fireplace

Solid fuel such as wood requires the factory chimney be listed to UL103HT, which is a 2,100F rated chimney. Older factory chimney such as used on oil fired heaters was listed to UL 103 without the optional HT high temperature rating. Those chimneys are rated for 1,700F. Look at the listing stickers to tell the difference.

Also, wood stoves will emit creosote deposits in the chimney.

HTH,

I should have explained myself better. While doing exterior surveys, I'm supposed to look for signs that there are fireplaces or wood stoves within the house. So ideally I'd like to be able to tell from the ground if there's a solid fuel burning appliance within. The part about the creosote helps. That's kind of what I've been going by so far. For instance, I reported the first chimney below but not the second, but to my uneducated eye they look pretty much the same, more or less. Is there anything special to look for in the way the top bit is designed, or are the main differences in the number of layers and insulation of the pipe?

Look for stacked wood piles in the yard. While not totally conclusive, it may add to the suspicion.

Also, hopefully Bob could answer this. Could looking at the height of the chimney provide any clues?

Hmmm, yes, height may be something to look at. Wood stove chimneys should be 3' higher than the roof where they pierce it, and 2' higher than the highest point within 10'. Not sure about other chimneys. Tired of searching for rules at the moment!

I'm a little confused about bends. The IRC says offsets must never be at an angle greater than 30 degrees from vertical, but there are all sorts of photos and diagrams on the 'net of metal chimneys making 90 degree angles, piercing a wall or masonry chimney horizontally.

There are several types of metal chimneys. Start here:
Types of Chimneys & Chimney Materials

Metal-Fab, Inc. - Residential Products for residential and light commercial venting applications

DuraVent : Old Browser Notification

You are allowed to make bends in the 'connector' or stovepipe up to almost 90 degrees from vertical while the 'chimney' cannot be more than 30* from vertical. That means while it's visible in the room, it can zig and zag a bit. You still must slope up 1/4" per foot, male end down, be properly secured and supported, etc. I would recommend never have seams down between 5 & 7 O'clock positions so condensate does not settle in the seam.

The 3/2/10 rule is for all 'chimneys', whether factory built or masonry. 'Vents' can be shorter per the code and appliance listing.

I hate to say it but you really need to inspect the pipe up close to determine what it is. This usually involves removing the rain cap to inspect inside as well.

My strongest advice is to take Dale Feb's FIRE course from the ad button below.

Originally Posted by Kristi Silber

Hmmm, yes, height may be something to look at. Wood stove chimneys should be 3' higher than the roof where they pierce it, and 2' higher than the highest point within 10'. Not sure about other chimneys. Tired of searching for rules at the moment!

I'm a little confused about bends. The IRC says offsets must never be at an angle greater than 30 degrees from vertical, but there are all sorts of photos and diagrams on the 'net of metal chimneys making 90 degree angles, piercing a wall or masonry chimney horizontally.

Most of these chimneys are tested and listed as "all fuel". While modern wood stoves are limited to UL 103HT type chimneys, as long as the chimney is properly sized they can also be used to vent gas, wood or oil. It is unlikely that you can look at the chimney and determine what fuel is in use unless you see a collection of creosote on the rain cap.

A factory-built fireplace is unlikely to have the same UL103HT type chimney. That kind of chimney typically complies with the UL103 standard as it is included in the UL 127 testing and listing for the fireplace. As mentioned, that chimney is tested to 1,700 degrees rather than 2100. The UL 127 listing includes the chimney. That chimney cannot be used for anything other than to vent the fireplace with which it was tested and listed.

Ashley Eldridge
CSIA Director of Education
Chimney Safety Institute of America

Location can also be a clue. If near an outside wall it would almost always be for a fireplace. Not 100% conclusive, but it would be likely.

Originally Posted by Ken Harbeck

Location can also be a clue. If near an outside wall it would almost always be for a fireplace. Not 100% conclusive, but it would be likely.

This is not a good way to determine what is venting into a chimney.

Originally Posted by Kristi Silber

I should have explained myself better. While doing exterior surveys, I'm supposed to look for signs that there are fireplaces or wood stoves within the house. So ideally I'd like to be able to tell from the ground if there's a solid fuel burning appliance within.... Is there anything special to look for in the way the top bit is designed, or are the main differences in the number of layers and insulation of the pipe?

I look for a size difference. It's been my experience that a normal gas vent is around 6"-8" whereas a wood fireplace chimney is more like 24".

(It's my understanding that the fireplace does not have a maximum limit on the amount of btu's it can handle (you can stack to logs on to any extent) and that's why it's so much larger).

I'm surprised that no one has differentiated between a chimney and a vent.

Well, yes Eric, you're right but there's also a limit as to how much we can and should discuss here. I mean, the best way to answer this information is to take some professional training on the matter because there are many aspects to this issue. It is not practical to teach an entire course here.

FYI, most factory built fireplace flues are 8-11" ID.

You need to document what you find but also what is venting into it then verify that this type of venting is suitable for that appliance and vice versa.

At the level of knowledge expected of me and considering how little I'm paid, a course on the subject is probably overkill. (I am not a regular HI, I survey/inspect houses for the insurance industry.) So I guess I'm going to have to make some educated guesses, based on viewing these things from the ground. No big deal, just thought there might be something particular to look for besides creosote.

Wood stoves ("solid fuel burning appliances") are major concerns to the insurance industry. Fireplaces aren't considered nearly the hazards wood stoves are.

Krisit1,

Just curious is to why Wood stove in the insurance eyes is worse then Open fireplaces.

Originally Posted by Mike Schulz

Krisit1,

Just curious is to why Wood stove in the insurance eyes is worse then Open fireplaces.

Good question. According to my training literature, solid fuel burning appliances are the single largest cause of heating fires in the US, the cause of 5-10% of "all fires" in the US (which I imagine means structural fires, or maybe home fires) and 300 deaths/year. They are considered a 5% value feature and 95% hazard, whereas fireplaces are 5% hazard and 95% value.

I can think of a few reasons why this might be. Wood stoves are more often used as a source of heat, so when people have them, they use them more often than people generally use fireplaces. They leave them unattended. Wood stoves are often added to a home, so proper installation of the chimney and maintaining appropriate clearances to combustibles may be more of an issue. Metal chimneys routed through a wall to the exterior before going to the roof may have more issues with creosote build-up than masonry because they're cooler.

There are probably other reasons, but those are ones I can think of offhand.

Take Bobs advice and take the FIRE course. Or in Canada WETT. I had a pretty good knowledge of wood burning until I took the code compliance course. Much of what I new was skewed by years of misinformation.
Stove are dangerous, a runaway stove will get very hot. If combustable wall and ceiling surfaces get to 90c, over time it can lead to pyrolisis and can ignite below normal temperatures (451f). Insurance companies keep me busy. It is one of the best courses I have taken as an HI.

I completed my WETT education and conduct level 1 SITE inspections.
Wood stove are installed in the most interesting places and combustables are overlooked, you would be amazed. When the fireplace was built the mason planned its location and included, in most cases a hearth pad. Its only later that someone added carpeting right up to it.

The variables and clearances are many for each wood burning appliance. We even a have a generic standard for unlisted stoves covered under CSA B365. Get a copy.

I think if you plotted a graph of the fire losses over the last 40 yrs. you'd see a spike in the incidence rate and deaths back in the early '80s then a steady decline with a few rises or humps over time. Now, correlate that plot with the economy and you'll find when the economy tanks, these rates go up as people turn to burning wood (and coal) for heat. Afterall, every man was born with the biological ability and knowledge to make fire and unfortunately, sometimes they do. The loss rates where a qualified professional did the installation, responsible owners operated it within the mfrs. instructions and did their due diligence in regular inspection and maintenace is very very low indeed.

You see, the insurance companies were paying us to inspect woodstove installations back in the early '80s, directly in some cases and in others by offering discounts in premiums to their clients if they called us to inspect. Everyone made money and less homes were incinerated. Then the insurance companies dropped the programs and people hardened to it so the rates rose a little. However, as time marches on, more and more of these blatantly dangerous installations get flushed out. The problem is unqualified installers (called "builders") who send the lowest paid most unqualified guy they can to do the install or install combustible shrouds and facings over hot things then marvel when it lights up.

If we took the approach of Europe making it a State controlled service, the losses would plummett but taxes would soar since this is a very political issue (another form of socialism). It seems to me the best solution would be to return to the days where the insurance companies put an incentive to get professional inspections. We have an excellent training certification program available to qualify inspectors so we have the knowledge and a lot of experience with fire losses and carbon monoxide injuries from hearth appliances, solid fuel appliances and combustion venting in general.

Originally Posted by Kristi Silber

Good question. According to my training literature, solid fuel burning appliances are the single largest cause of heating fires in the US, the cause of 5-10% of "all fires" in the US (which I imagine means structural fires, or maybe home fires) and 300 deaths/year. They are considered a 5% value feature and 95% hazard, whereas fireplaces are 5% hazard and 95% value.

I can think of a few reasons why this might be. Wood stoves are more often used as a source of heat, so when people have them, they use them more often than people generally use fireplaces. They leave them unattended. Wood stoves are often added to a home, so proper installation of the chimney and maintaining appropriate clearances to combustibles may be more of an issue. Metal chimneys routed through a wall to the exterior before going to the roof may have more issues with creosote build-up than masonry because they're cooler.

There are probably other reasons, but those are ones I can think of offhand.

Actually Kristi the double-wall insulated factory-built chimney is much more likely to keep the flue gases elevated and provide more draft to the appliance while keeping heat transfer to surrounding combustible materials minimized than a traditional masonry chimney exposed to the exterior will.

Ashley Eldridge
CSIA Director of Education
Chimney Safety Institute of America

Ashley, thank you for the correction. I had read that exterior metal chimneys have more problems with creosote build-up than interior metal ones, but the comparison with masonry chimneys was a guess, and I should know better than to guess about something like that!

I can definitely see the value of taking the course suggested if I'm going to be an HI, but right now it would be wasted. Most insurers require a fairly detailed form be filled out if I come across a wood stove, including things like who installed it and was it inspected, whether it's serviced regularly, lots of questions about clearances, the chimney, UL listing, etc. Completing this form is the single reason I'm allowed to enter a house if I'm doing an exterior (and not interior) survey - a measure of how important to them it is. Apparently many insurers have switched from using better-trained (and more expensive) inspectors to using field representatives like me to provide their data about the stoves, but at least someone is doing it.

One day maybe I'll take the course, when I can afford to spend a few thousand to do it.

Thanks very much everyone for your input!

Old tripled walled air cooled thermosyphon chimneys can run so cool they actually gunk up with creosote faster than some masonry chimneys at similar burn rates, especially when located on an outside wall.

To Dennis, the UL 127 test makes it hard to overfire a factory built fireplace compared to the Flash Fire test during listing but that is not a condition of normal useage. These things are not trash incincerators. For those who approve of vented gas log installation, they typically limit them to a max. of 100,000 BTU/hr.

Kristi, it would be prudent for the insurance companies to at least recommend all fireplaces and hearth appliances be installed by a qualified inspector annually. That's what most mfrs. put in their manuals btw. You are to be commended for the work you do but also for striving to continue your education and raise the bar. Thx!

Originally Posted by Bob Harper

Old tripled walled air cooled thermosyphon chimneys can run so cool they actually gunk up with creosote faster than some masonry chimneys at similar burn rates, especially when located on an outside wall. Yeah, I was just reading about these yesterday. That's another thing I wish I could tell from the ground.

To Dennis, the UL 127 test makes it hard to overfire a factory built fireplace compared to the Flash Fire test during listing but that is not a condition of normal useage. These things are not trash incincerators. For those who approve of vented gas log installation, they typically limit them to a max. of 100,000 BTU/hr.

Kristi, it would be prudent for the insurance companies to at least recommend all fireplaces and hearth appliances be installed by a qualified inspector annually. Yes indeed! Unfortunately I'm not supposed to make any type of recommendations to homeowners, which is one of the most frustrating parts of my job sometimes. I often wonder what safety issues get passed on to them. That's what most mfrs. put in their manuals btw. You are to be commended for the work you do but also for striving to continue your education and raise the bar. Thx!

And thank you for the compliment, and for helping me to continue that education!