flue too short?

Extend a flue ?

https://www.hearth.com/econtent/index.php/forums/viewthread/8/

diyguy said:

I'm installing my vermont castings small dutchwest catalytic stove in my living room through the existing fire place. From the top of the terracotta to the floor of the fireplace is 13 feet. That gives me a funtional flue length of 11 feet from the top of the stainless steel flex liner to the Tee. I'll have about 1 foot of horizontal pipe connecting the Tee to the stove. I plan on insulating the top and bottom of the chimney liner, as well as installing a blockoff plate. My concern is that the stove manual tells me the chimney should be at least 16 feet! The existing chimney top is about 2 feet above the peak of the house and has one warm inside wall and 3 sides of unheated garage around it. The flue interior dimensions are 6 5/8" by 10 1/4". My concern is whether this is workable insulating with the ceramic blanket top and bottom. I don't think there is adequate room for wrapping the liner with the faced insulation. The other possibilities I've been considering are as follow:
1. pouring the liquid insulation around the liner
2. using a flue stretcher (I'm skeptical of this one: smoke hitting cold stainless stretcher will slow down/cool negating the extra length)
3. extending the terracotta above the existing chimney. I'm not a big fan of this one either, because I'm no mason.

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option 3 just extending a clay flue, besides not code compliant, is not a way to achieve the length, unless you are building the chimney surounding it

What about retrofitting a Class A stainless steel flue to extend your length.
Actunally why not purchases a prodect tested to solve your problem Extenda flue?

Calling extenda flue to the answer desk. Paging extenda flue guy.

Insulation around your existing liner will help create better draft but I don't think anyone can tell you the insulation makes up for 5' missing of verticle length.

diyguy said:

ok, so you guys like extenda flue. Will it fit into the top plate that came with the SS liner kit? Is it possible to install what I have; if that doesn't draft satisfactorily, then add the extenda flue? The extenda flue models range from 30 to 40 inches of additional flue and range from $425 to $795. Are they a cost effective solution considering that they don't bring the chimney to the 16 feet either?

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There is certainly no harm in trying what you have to see if it works - you might get lucky, some folks do. It certainly won't hurt to do everything you can to improve your draft, such as insulating the liner as much as you can, keeping the horizontal run as short as possible, and pitched up as much as you can, etc. If you are lucky it will "just work" - if not, you will need to figure out some way to increase your effective stack height, but how much is an unknown... The extendaflue is certainly one way, but given it's cost, I would probably try to figure out some way to improvise some temporary extensions (note that this isn't really legal or 100% safe) to experiment and find out just how much extra you need. After determining that, then you will have to decide the best way to accomplish it permanently that is safe and legal. If they will do the job, the extendaflue is probably the easiest and least expensive approach - hiring a mason to extend the brick chimney would probably cost more, and might require you to get a new liner to fit the taller chimney (I'm not sure about that - it may be possible to just splice on an extension....)

The only way to find out for certain is to experiment because every setup is different, and there are too many unknowns to make any kind of prediction without the experiment.

Gooserider

goose are you adviing this guy to install a stove that does not meet the listing requirements? Verticle heigh is a listing requirement needed to be obtained to pass inspections.

First of all I would not have issued a permit if the verticle height could not be satisfied. Are you advising of a non compliant .non permitted, listing violation. installation ?

We are not talking about 6" but 5.' Are you willing to take on the responsibility, when that chimney does not produce enough draft and tell him his home filled up with smoke and carbon monoxide its ok?

elkimmeg said:

goose are you adviing this guy to install a stove that does not meet the listing requirements? Verticle heigh is a listing requirement needed to be obtained to pass inspections.

First of all I would not have issued a permit if the verticle height could not be satisfied. Are you advising of a non compliant .non permitted, listing violation. installation ?

We are not talking about 6" but 5.' Are you willing to take on the responsibility, when that chimney does not produce enough draft and tell him his home filled up with smoke and carbon monoxide its ok?

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Well, according to the OP, the extendaflue that you are reccomending at 40" max extension is not going to be compliant either.... (5 feet = 60")

What I was reccomending was EXPERIMENTATION - there is an outside shot that a short flue that is otherwise OK (he does have the right X section diameter, meets the 2/3/10 rule, and the chimney's at least protected from the wind) MIGHT work, and if not I was suggesting he try TEMPORARY extensions to see how much length he needs to get a *functional* setup. THEN making whatever permanent changes he would need to get that amount of extension....

I may be misinterpreting the manual, but when I see them talking about chimney height, they say "RECOMMENDED minimum height" - they did NOT say that this was a required height the way they say that clearances are REQUIRED.... My usual interpretation is that when something is "reccomended" it is considered desirable, but is not an "absolutely must have". IOW, I don't thing VC is saying that the stove would be unsafe or not work with an 11' chimney, but that they think a 16' or higher chimney is best.... I did NOT see a listed REQUIREMENT for a minimum vertical height (and note that their recomendation changes with altitude, something that the OP hasn't even mentioned)

I don't know what the "minimum stack height" is on my smoke dragons, but I had quite a nice draft with a FOUR foot high stack at one point when I was testing it outside, in warm weather... I also see lots of single story ranches with chimneys that certainly don't look like they came off of factories, so I feel sure that at least some homes may draft allright with shorter than reccomended chimneys.

I didn't define conditions when experimenting, but that usually would imply extra levels of alertness, and doing small fires that could be dealt with if a given test did not work... Obvioiusly getting smoke and CO in the house is not OK, this is why I said TEST to find out what is needed to NOT get smoke and CO problems. (Something that neither you or any of the other extendaflue advocates suggested.... ) I do not think it makes sense to go out and spend $800 on a 40" extendaflue (that still doesn't bring him up to the reccomended 16') without evidence that doing so would actually give him a working installation.

If I was in his shoes, I would probably get a few peices of 6" single wall and stick it into the top of his chimney on a TEMPORARY basis. (If I could figure a way to secure it adequately, I might use 8/8 flue tile instead)I'd try that in different lengths until I found what length gave me a properly drafting chimney - and then modify the existing chimney IN A COMPLIANT MANNER to give me that height - the end result is a compliant installation that WORKS, without wasting money on expensive approaches that might not be adequate.

Instead of flaming me about suggesting that the OP might want to experiment before spending lots of money, you might have answered the question I raised about IF he decided to extend the masonry chimney to give him more height would he need to replace his entire liner, or would it be OK to splice another peice onto it? IMHO that would be more useful...

Gooserider

if the liner is in good shape he probably could remove the top section anf the cap area and extend up but again even masonry chimneys need support when not supported on the side or threw the framing. the other issue is if it contained another flue t probably that too would need extending.

Another way to solve the issue is review other comparable manufactures stoves and go with the one with the lowest verticle height requirement

It would be asking me a lot and a reach to expect me to issue a permit when the height is 5' short. remember that is the miniun distance beyond that lead to better drafts ans stove preformance

Good that it can be extended if he needs to, and agreed that any overly tall chimney needs added support (not sure what the definition of "overly tall" would be, but thats a seperate question) If it's a multi flue chimney, that adds to the problems but it's still something that would be doable.

Your idea about looking at a different stove isn't bad, but from the OP, it looks like this is an already owned stove, so that isn't a real palatable idea - plus I'm not sure that there are many stoves out there with shorter height recomendations - most every stove I've looked at has been about the same - not that I've worried that much about it since our setup tends in the opposite direction.

I agree the 11' height is pretty bad, but I didn't feel comfortable advising him to go straight to the Extendaflue until he had experimented to find out what he actually needed. He might get lucky with the 11' setup, but frankly I'd be surprised. I'm more inclined to think that the 40" extendaflue might not be ENOUGH so he should find that out first.

Gooserider

diyguy said:

ok, that's more like it. I was worried that you guys were too sedate, but you proved me wrong.
I already own the VC stove, so there's no shopping for shorter flue lengths. I think 16' is pretty much the standard recommended flue length out there anyway.
In my ideal world I would have woodstoves both upstairs and downstairs. The VC stove is probably a little too much for the upstairs; I'd prefer to install it downstairs.
I posted here a few weeks ago when I tried to install the stove in the basement using a comealong to rip the liner into place. I think y'all responded to that sad story as well. I pulled it back out and amazingly enough only about 3 feet are beat up and even that is only dented and ovalized with no tears. I have 22 good feet of liner left. Dare I ask it, but I have another question about my basement chimney. It requires you to use your imagination. Picture yourself with a hammer and chisel. You're removing the firebrick from that back of the fireplace, especially the smoke shelf. You remove the brick, ash, and debris. You are all done. All of the firebrick, dirt, and cement is gone. What do you see? Remember, you are below grade working on a basement chimney. The house is a ranch in a northern rust belt suburb.

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Well, I believe its sort of uncool to take bricks out of the fireplace, though you might need to IIRC your previous posts... That said you tone sounds like it was something alarming - and I would have three guesses...

1. Structural wood that shouldn't be there.

2. Since you are below grade - Dirt or equivalent, as in no foundation or fill that should have been there....

3. Construction debris that shouldn't be there either, but gets found in such places all to often.

Gooserider

Well. all I've seen says that it is OK to cut the metal damper box frame, although if you do the firebox must be permanently marked as having been modified and no longer suitable for use as a fireplace - Some inserts come with signs to do this. I believe if you modify the damper box, the bottom blockoff plate needs to be lower than the modifications, or at least seal them in some way.

However AFAIK it is NOT OK to actually remove bricks from the firebox itself.

Can Elk or one of the other code guru's confirm?

You have a bit of a dilemma, that is plain. Most folks say that it isn't a real good idea to put a stove in the basement as that can give less than optimal heating. OTOH, it sounds like your upstairs flue isn't tall enough. Have you thought of adding a second floor? ;-)

Gooserider

To clarify goose, you can remove masonry or steel from the smoke shelf (the back of your fireplace) and/or damper frame if necessary to accomodate a chimney liner provided it doesn't weaken the structural integrity nor reduce protection for clearance to combustibles to less than required by the national building code. Currently, my fireplace has the firebrick removed from the smokeshelf in the back, my mason afterward to be safe covered the entire inside of my fireplace with some insulation good to 2300F I think it's made of slag.

I knew it could be done because my manual page 12 last paragraph says something to that affect. I was happy to see that, couldn't have gotten the liner in otherwise.

Chimney sounds short - on the extendaflue end, what you can do is buy the external castings only and an adapter and then run your liner up through it - not masonry, etc. needed. Gives you about another 3 feet which can make a big difference.

If you want to experiment first, run that liner up an extra three feet, wrap insulation around it and fire away for a day or two. If this works, then the extendaflue will work - and of course look and function much better.

I think cutting or grinding the damper plate is OK, although I prefer when possible to ovalize the pipe so fireplace can be restored easier in the future if desired. Removing an inch or so of the masonry right there in the rear of the damper frame would also be safe if FP was properly constructed....but I would personally not remove whole bricks if possible. As a rule of thumb I'd want to see 12" min of solid masonry between the pipe and the framing on the rear of the fireplace (if fireplace is interior). If it is exterior, then there should not be any danger at all from rearward radiation.

Depends on which size, etc.

You may need the larger castings if you have a large flue tile sticking up (12x12). This would be approx $500 including the castings/adapter/cap, etc.

PM or email me if you have more interest - let me know flue size, whether it sticks up from cement crown, etc.

diyguy said:

I have a bit of a dilema here and the core of it really revolves around installing the stove in basement. That's what I started to do, but I couldn't get the 6" liner into place. I had an estimate from a local company to come in and install a liner a couple of years ago. They wanted to do surgery on the downstairs fireplace to make it work. That's why I asked earlier about what I might find if I dig into the smoke shelf area. I think it would be best to install the liner I have in the basement chimney, since I have said liner. However, it seems to be a technically more difficult to do. I'm wondering if I should repost and start a new thread about how to make this project work.

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Your choice on starting a new thread. My personal preference is to keep everything in one thread as it makes it easier to keep track of the background info, and / or saves you reminding us of stuff again, but it's up to you.

To me the big question about a basement install is whether you are really trying to heat the basement because it's active living space and heat to the rest of the house is a bonus, or if you are really just wanting to heat the rest of the house.

It is hard to make the heat go down, so usually the best choice is to install at the lowest floor you need the heat at, and let it work it's way up. However if you don't NEED to heat the basement, there are multiple reasons not to go there - Basements are hard to heat efficiently, as they tend to be heat sinks that will hurt the stove performance. Because of the various issues detailed in other threads, it can be hard to get good draft in a basement. Last, but far from least, stoves are space heaters, not furnaces, and they are most effective when installed in the places that you are most wanting to heat, rather than heating one area and trying to move the heat to someplace else...

That said, minor surgery on the basement fireplace shouldn't be a huge problem, unless you have reason to think that it wasn't built to code, or is otherwise problematic (which should also mean that you don't want to use it as a normal fireplace either....) See some of the earlier posts about what level of surgery is safe.

Gooserider