Help! Chimney liner issue question

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.
Status
Not open for further replies.

StumpFJ40

New Member
Jan 14, 2011
5
Philly 'burbs
Hi,
I've been lurking for a while as I decide on a wood burning insert. I've done a ton of searching and can't quite find the answer to my specific situation.
I knew the chimney in our house had been relined... upon close inspection I identified the liner as a 7"x9.5" rectangular stainless steel line set in some type of cement medium. Our house is a 250yr old stone farm house. The chimney is inside the house and is approx 25-30 ft tall. The fire box is 36"w x 25"h x 15"d. The flue damper is a spring loaded unit at the top of the chimney. I am looking at a Regency I1200 or Dutchwest size insert due to the depth constraints in my fireplace.

So I humbly submit the following question: Is it feasible to use a length of 6" flex pipe between the insert and the bottom of the 7x9 rectangular liner? I know the rectangular liner has a cross-sectional area of approx 63" and the 6" flex pipe's area is approx 28.2"... Will this cause significant draft issues? From what I've read, I could put another 6" liner in the chimney, but that will certainly be difficult with two corrugated liners passing along 25 feet.

Thank you in advance for your help/guidance

Cheers,
Stump
 
Welcome Stump. The flue is tall and may draft ok. But I'm wondering if a small insert will do the job. How large a space will you be trying to heat? Is the insert room open to the rest of the house or closed off by small doorways?
 
My Jotul insert was professionally installed. The chimney tile liner was too big to suit the new stove. The stove was designed to work with a 6 inch, no larger, stack. I believe the space between the old tile and the new liner is where the combustion air comes in. So the stove will not suck heated air from your house.
 
Cal, I'm not sure that is correct. The chimney is a sealed space with a limited air supply. Unless an OAK is connected, the stove is pulling its combustion air from the house.
 
BeGreen said:
Cal, I'm not sure that is correct. The chimney is a sealed space with a limited air supply. Unless an OAK is connected, the stove is pulling its combustion air from the house.
Well then, your insert is designed differently than my Jotul 550 is. Mine does not use room air. When all else fails, read the manufacturer's instructions. <<g>>
 
BeGreen...... this is one of those moments where your quote in your signature rings true........ the second one.
 
Cal-MI said:
BeGreen said:
Cal, I'm not sure that is correct. The chimney is a sealed space with a limited air supply. Unless an OAK is connected, the stove is pulling its combustion air from the house.
Well then, your insert is designed differently than my Jotul 550 is. Mine does not use room air. When all else fails, read the manufacturer's instructions. <<g>>

You are just flat wrong. End of discussion.
 
Cal-MI said:
BeGreen said:
Cal, I'm not sure that is correct. The chimney is a sealed space with a limited air supply. Unless an OAK is connected, the stove is pulling its combustion air from the house.
Well then, your insert is designed differently than my Jotul 550 is. Mine does not use room air. When all else fails, read the manufacturer's instructions. <<g>>
It sounds like you have an outside air kit somehow rigged up, I am not sure how outside air would be hooked up to an insert. In order to pull combustion air from around your liner, the liner could not be terminated at the top properly.
 
BrotherBart said:
Cal-MI said:
BeGreen said:
Cal, I'm not sure that is correct. The chimney is a sealed space with a limited air supply. Unless an OAK is connected, the stove is pulling its combustion air from the house.
Well then, your insert is designed differently than my Jotul 550 is. Mine does not use room air. When all else fails, read the manufacturer's instructions. <<g>>

You are just flat wrong. End of discussion.
You are making assumptions. The installer said it did not use room air. I am just quoting the professionals. The manual shows the stove drawing combustion air in the back. I do not personally know what that space is connected to, how it was installed. The manual shows different installations for the US and Canada and for masonry and manufactured fireplaces. It also showed one with the space between and tile and the liner vented at the top and another installation sealed at the top.
 
If there isn't a OAK installed, OAK meaning outside air kit, that insert is burning using air from the living space. Not some dream world outside.
 
BrotherBart said:
If there isn't a OAK installed, OAK meaning outside air kit, that insert is burning using air from the living space. Not some dream world outside.
Yup. I assume there is one. I know there is room for one. Two different types. Maybe in the summer I will disassemble a few things and check. YMMV.

Back to the original question, some installations require an air space between the liner and the old flue. And most modern stoves work best with a certain sized flue, smaller than old style stoves needed.
 
Hi -

I'm familiar with some old stone work.

If it was mone I'd verify that a weighted can of about 6 1/2" can be lowered all the way down. Then i'd slide 6" ridgid or flex in there.

My reasoning is I'd reduce the termal shock/cycling on the old chimney, and is easy to clean. I'd also consider a stove backed up to the FP opening if the room will hold it. It's a good deal more efficient for heating.

ATB, sound like a nice old place,
Mike
 
StumpFJ40,

"The flue damper is a spring loaded unit at the top of the chimney."

If this is what you have, note the last line of the desription: "SEAL TIGHT Dampers are made for use only with open burning masonry fireplace chimneys and are NOT suitable for use with fireplaces burning gas logs, or where wood stoves have been installed."

http://thefireplaceandchimneyshop.com/product.asp?intProductID=84
 
All,

Thank you for the responses! I cherry picked a few of your inputs that address my issue.

BeGreen said:
Welcome Stump. The flue is tall and may draft ok. But I'm wondering if a small insert will do the job. How large a space will you be trying to heat? Is the insert room open to the rest of the house or closed off by small doorways?

Thank you for the welcome! I've found this site incredibly informative to a wood stove/insert NOOB like myself. I am sold on wood heat and continue to strive to understand the science and art of the burn.

I knew I forgot some details! The room the insert will be placed in is about 528sqft with an 8'6" ceiling ( 28'x24' main house with 18" stone walls with a 36" opening in the middle of the 28' wall going into the dining room that is 20'x16') The chimney is on the north wall of the house. The kitchen is beyond that and is the back end of the house. The total sqft of the house is approx 2150 sqft. I have a VC Intrepid wood stove in the dining room that I have restored and am close to putting into service. There are two stairwells that are fairly open and allow heat to rise to the second floor.
I am looking to warm the main room as well as cut some vents in the floor to allow the heat to rise into the bedroom that is directly above the fireplace.

zzr7ky said:
Hi -

I'm familiar with some old stone work.

If it was money I'd verify that a weighted can of about 6 1/2" can be lowered all the way down. Then i'd slide 6" ridgid or flex in there.

My reasoning is I'd reduce the termal shock/cycling on the old chimney, and is easy to clean. I'd also consider a stove backed up to the FP opening if the room will hold it. It's a good deal more efficient for heating.

ATB, sound like a nice old place,
Mike

Thanks for the advice Mike, I will certainly try that... I have a VC stove I mentioned above, but I'm not sure if it would fit.
Deep down, I know the right thing to do is send a 6" liner down the chimney, but I seems a shame to waste a perfectly good lined chimney by putting yet another liner in.

The house is a great old place the original farmhouse probably the most well constructed part of the house!
Cheers,
Stump

DanCorcoran said:
StumpFJ40,

"The flue damper is a spring loaded unit at the top of the chimney."

If this is what you have, note the last line of the desription: "SEAL TIGHT Dampers are made for use only with open burning masonry fireplace chimneys and are NOT suitable for use with fireplaces burning gas logs, or where wood stoves have been installed."

http://thefireplaceandchimneyshop.com/product.asp?intProductID=84

Yes, I understand that I would have to remove the damper or pin it open once I install an insert. If I were able to hook directly to the existing 7x9.6 liner, I would pint the damper open and put a stainless steel screen around the top.

Does anyone have some math/formulas that would allow me to calculate my draft if connected the 6" liner to the 7x9.5" liner with the stoves mentioned in the OP?

Thanks again for the inputs! Keep 'em coming... What are the potential issues relating to efficiency and safety with my idea of connecting directly to the 7x9.5" with the 6" flex liner? I do not believe in running the 6" part way into the chimney and using a block-off plate because I know that makes cleaning difficult. So, it's either adapt 6" round to 7x9.5" square or run 6" all the way up.

Cheers,
Stump
 
Another question:

Most installation manuals state that the insert must not be connected to a chimney with an area more than 3 times the area of the flue collar. 6" round liner= 28.27 sqin; 7x9.5" square liner= slightly less than 66.5 sqin (with rounded corners). My flue is approx 30 ft tall. Again, the chimney is built into the house. I can't find anything that dissuades me from fabbing a 6" round to 7x9.5" square funnel to join the 2 liners. If anything, I'm concerned that 30 feet of 6" liner will draft like a blast furnace and over fire a small to medium insert.

What say you?
 
jotulguy said:
BeGreen...... this is one of those moments where your quote in your signature rings true........ the second one.

:lol:
 
StumpFJ40 said:
Another question:

Most installation manuals state that the insert must not be connected to a chimney with an area more than 3 times the area of the flue collar. 6" round liner= 28.27 sqin; 7x9.5" square liner= slightly less than 66.5 sqin (with rounded corners). My flue is approx 30 ft tall. Again, the chimney is built into the house. I can't find anything that dissuades me from fabbing a 6" round to 7x9.5" square funnel to join the 2 liners. If anything, I'm concerned that 30 feet of 6" liner will draft like a blast furnace and over fire a small to medium insert.

What say you?

So Stumpy, a 6 inch liner has a cross section area of about 28.27 inches squared, then X 3 = about 84 square inches, the maximum flue liner size allowed for an inside chimney for an appliance having a 6" flue collar. So if your existing SS liner is 7X9.5 = 66.5 square inches, then connecting two SS liners would not violate code, assuming that the existing rectangular liner meets code. That's where the rub comes in, I think, is that you don't know if the existing liner is UL listed, or what are it's temperature operating limits. It may be perfectly OK. The problem is that you may not know what you've got.

Both NFPA 211 and the IRC require masonry chimneys to be lined. Each specifies the type of material allowed for different applications and the methods and materials for installation of liners. I suggest that you might want to check with the experts and see what these codes require.
 
volemister said:
StumpFJ40 said:
Another question:

Most installation manuals state that the insert must not be connected to a chimney with an area more than 3 times the area of the flue collar. 6" round liner= 28.27 sqin; 7x9.5" square liner= slightly less than 66.5 sqin (with rounded corners). My flue is approx 30 ft tall. Again, the chimney is built into the house. I can't find anything that dissuades me from fabbing a 6" round to 7x9.5" square funnel to join the 2 liners. If anything, I'm concerned that 30 feet of 6" liner will draft like a blast furnace and over fire a small to medium insert.

What say you?

So Stumpy, a 6 inch liner has a cross section area of about 28.27 inches squared, then X 3 = about 84 square inches, the maximum flue liner size allowed for an inside chimney for an appliance having a 6" flue collar. So if your existing SS liner is 7X9.5 = 66.5 square inches, then connecting two SS liners would not violate code, assuming that the existing rectangular liner meets code. That's where the rub comes in, I think, is that you don't know if the existing liner is UL listed, or what are it's temperature operating limits. It may be perfectly OK. The problem is that you may not know what you've got.

Both NFPA 211 and the IRC require masonry chimneys to be lined. Each specifies the type of material allowed for different applications and the methods and materials for installation of liners. I suggest that you might want to check with the experts and see what these codes require.

Good point, I think I am at that point where I need to have the AHJ come and take a look. Unfortunately, I find that I often have more information and understand the issues better than the local AHJ's I've dealt with in the recent past. I just installed a new kitchen, meaning moved the entire kitchen to a different location and installed new plumbing, electrical, lighting, flooring... everything using zero contractors. The inspectors/AHJ's seemed more interested in getting their buddies some work than actually assessing my plan and issues on it's merits. I also seemed to know more about the codes than they did. It reinforced my impression that the system is nothing more than a money grab.

Is there any simple method for calculating the draft potential of a chimney? Like height vs. cross sectional area?

Cheers,
Stump
 
StumpFJ40 said:
volemister said:
StumpFJ40 said:
Another question:

Most installation manuals state that the insert must not be connected to a chimney with an area more than 3 times the area of the flue collar. 6" round liner= 28.27 sqin; 7x9.5" square liner= slightly less than 66.5 sqin (with rounded corners). My flue is approx 30 ft tall. Again, the chimney is built into the house. I can't find anything that dissuades me from fabbing a 6" round to 7x9.5" square funnel to join the 2 liners. If anything, I'm concerned that 30 feet of 6" liner will draft like a blast furnace and over fire a small to medium insert.

What say you?

So Stumpy, a 6 inch liner has a cross section area of about 28.27 inches squared, then X 3 = about 84 square inches, the maximum flue liner size allowed for an inside chimney for an appliance having a 6" flue collar. So if your existing SS liner is 7X9.5 = 66.5 square inches, then connecting two SS liners would not violate code, assuming that the existing rectangular liner meets code. That's where the rub comes in, I think, is that you don't know if the existing liner is UL listed, or what are it's temperature operating limits. It may be perfectly OK. The problem is that you may not know what you've got.

Both NFPA 211 and the IRC require masonry chimneys to be lined. Each specifies the type of material allowed for different applications and the methods and materials for installation of liners. I suggest that you might want to check with the experts and see what these codes require.

Good point, I think I am at that point where I need to have the AHJ come and take a look. Unfortunately, I find that I often have more information and understand the issues better than the local AHJ's I've dealt with in the recent past. I just installed a new kitchen, meaning moved the entire kitchen to a different location and installed new plumbing, electrical, lighting, flooring... everything using zero contractors. The inspectors/AHJ's seemed more interested in getting their buddies some work than actually assessing my plan and issues on it's merits. I also seemed to know more about the codes than they did. It reinforced my impression that the system is nothing more than a money grab.

Is there any simple method for calculating the draft potential of a chimney? Like height vs. cross sectional area?

Cheers,
Stump

Hi Stump:

The technical calculation results in answer, I think, given in inches of water column. I'll have to consult my air quality engineering books on this one. Some years ago I used to perform what is called stack sampling of industrial plants - and I used such calculations...Oh so very long ago... We were interested in SO2 emissions, etc. Then I changed careers.

Anyway, an answer in "inches of water column" is probably not useful to you as a guide in how your particular stove will draft. Qualitatively, however with a 30 foot flue, you should be able to create quite a draft. There is a point of diminishing returns, of course, where a taller flue results in reduced draft. But I don't think you've reached that at 30 feet.

If you are going to purchase the wood stove anyway, you could obtain a short length of 6 inch SS Flex, connect it to your existing flue with a fabricated connector and see what happens. Here again, one still has to consider what that existing 7x9.5" liner is all about. But I think that you will have plenty of draft. Worst case is that you have to install a full 6 inch liner inside your 7x9.5" liner. Seems like it should fit.

Dang, I guess I'll have to root for the Steelers. My favorite New England Patriots just got eliminated...
 
volemister said:
Hi Stump:

The technical calculation results in answer, I think, given in inches of water column. I'll have to consult my air quality engineering books on this one. Some years ago I used to perform what is called stack sampling of industrial plants - and I used such calculations...Oh so very long ago... We were interested in SO2 emissions, etc. Then I changed careers.

Anyway, an answer in "inches of water column" is probably not useful to you as a guide in how your particular stove will draft. Qualitatively, however with a 30 foot flue, you should be able to create quite a draft. There is a point of diminishing returns, of course, where a taller flue results in reduced draft. But I don't think you've reached that at 30 feet.

If you are going to purchase the wood stove anyway, you could obtain a short length of 6 inch SS Flex, connect it to your existing flue with a fabricated connector and see what happens. Here again, one still has to consider what that existing 7x9.5" liner is all about. But I think that you will have plenty of draft. Worst case is that you have to install a full 6 inch liner inside your 7x9.5" liner. Seems like it should fit.

Dang, I guess I'll have to root for the Steelers. My favorite New England Patriots just got eliminated...

Volemister,

Thanks for your continued input and advice regarding my "issue". Indeed I have a couple feet of leftover 6" SS flexpipe from my stove install, where I used a full liner. My consideration for the mating of the 6" round to the 7x9.5" rectangle is to try to make the transition as "funnel like" as possible in hopes of eliminating the need to dismantle the stove to chimney flue connection during cleaning. Not to mention the underlying motivation of cost... not a huge motivator but always a consideration.
Also, it may be of little consequence, but there is no lower damper or typical "jog" at the top of the firebox and the chimney is a straight vertical shot bottom to top.
Cheers,
Stump
 
Status
Not open for further replies.