Ovalized liner or cut out larger damper (sic?) opening?

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Daniel

New Member
Sep 11, 2007
25
Eastern PA
Had my chimney cleaned yesterday and now I am getting ready to install an insert, but damper opening on existing fireplace is 4" X 36". Any advantages or disadvantages to ovalizing 6" liner or would it be best to use saw and cut out a 2.5" section of non-moving metal portion of damper to keep 6" round the whole length. I know that once I cut out a section of damper the insert is going to be a permanent fixture. I am planning on making a sheet metal block off plate after liner is in place. Any insights are appreciated. Thanks!

dan
 
I vote for cutting out the damper frame. That is what I did. Mashing the liner down just makes for a hassle cleaning the pipe plus you will have to "re-round" it to fit the flue adapter on the insert. Too much chance of screwing up the liner for my taste.
 
BB
Thanks for your insight. I actually found a forum thread that dealt with this topic in some depth and I think your advice makes sense. If I sell the house years from now I can't imagine taking the insert with me so why not do the job in a way that will help with draft. I got a kick reading your old post about being creamated in a woodburner. The humor (and good practical advice and insights) is what makes this sight enjoyable.

Dan
 
I cut my damper and the liner came almost straight onto the insert. Makes real nice for cleaning the liner.
Theres a thread with photos I posted somewhere.
 
Best thing I have heard to use is a grinder and a cut-off wheel. You can prob find one to borrow or rent one cheap, or just buy one for like $40, could come in handy for other stuff. A Sawzall with carbide or metal blades don't work that great on the old dampers, trust me we have tried it before. You go through quite a few blades.
 
I took my damper out. There were only two cotter pins holding it in. I cut a whole in for the liner and then cut it in half to make it easier to put back in. All I have left to do is seal it and I have an instant precut block off plate, and through a PM. I can say it's Elk approved.
 
I cut mine out with both a 4-1/2" grinder with carborundum blades thats plural BLADESSSSSSSSSSS.
And a sawzaw with heavy duty blades. Both made the job much easier than it could have been.
Both had their uses and could get where the other could not, or make it easier than the other.
 
I started off with all of that stuff and on the third Sawz-All blade I just went and got the hacksaw and it was done in a few minutes. With just one blade. No sparks, no teeth shaken out or anything.
 
Thanks Guys:

Just got out of the shower and removed the layer of soot, concrete dust, ash, leaves, and whatever else accumulates behind the damper edge. I actually found a tennis ball that looked like it was there from the 70's. So far so good the sawzall has cut two East - West cuts....now the hard part is going to be connecting them with a North - South cut. I think I might give the old grinder a crack at that line. Next question how stringent / important is manufactured recommended chimney height? Unit calls for at least 15' chimney and mine is 12' (live in a rancher) so I'm planning on a rigid pipe to get the extra heigth. Do most stoves have chimney height requirements? Never saw this figure in the basic specs of any stove manufacturers brochures or websites.

Thanks for your insights,

Dan
 
Log-a-rhythm said:
Thanks Guys:

Just got out of the shower and removed the layer of soot, concrete dust, ash, leaves, and whatever else accumulates behind the damper edge. I actually found a tennis ball that looked like it was there from the 70's. So far so good the sawzall has cut two East - West cuts....now the hard part is going to be connecting them with a North - South cut. I think I might give the old grinder a crack at that line. Next question how stringent / important is manufactured recommended chimney height? Unit calls for at least 15' chimney and mine is 12' (live in a rancher) so I'm planning on a rigid pipe to get the extra heigth. Do most stoves have chimney height requirements? Never saw this figure in the basic specs of any stove manufacturers brochures or websites.

Thanks for your insights,

Dan

Most say 15 feet. What is the elevation where you live?
 
Elevation in PA is not as high as say Colorado and such. There's mountains, but I don't think enough elevation to affect a chimney & stove.
I went about 1-1/2' out the top with the rigid. I didn't need to, but thats the shortest I could get without being about a few inches too short.
We don't have the thin air like out west.
 
Whoops. Elevation 39 feet. I would get as close to fifteen feet on the pipe as I could.
 
Log-a-rhythm said:
Not sure of my elevation exactly, but I live in the Philadelphia suburbs.

dan

I grew up in the Philly Burbs. Well Feasterville, then Southampton, Langhorne, Warminster, Hatboro, then lived in Warrington for almost 18 years. Now I am a hick in the sticks of Berwick :)
 
Some locals/installs 12' will work just fine, other places it won't. I'm a strong proponent of good draft, I had bad draft and don't wish that experience on even my enemies. You can't keep your glass clean, really hard to get your fire started, reloading causes tons of smoke to pour into the living space (and often set the whole house smoke detectors off), the spilled smoke made the place dirty, and I couldn't even think about lighting a fire if it was warmer than 45F outside. I had a number or problems, a short chimney, the chimney wasn't enclosed in the attic space which made my inside chimney part of the outside envelope, an overly ovalized flex pipe going through the damper, and mis-branded connection pieces caused gaps in my liner. I ended up ripping out my entire install, enclosing the attic space around my chimney with metal, cut my damper so I didn't have to ovalize, purchased a new round flex pipe, removed the mis-branded connectors, and purchased an extend-a-flue to increase my chimney height 4'. It's such a joy to use now, and no more dirty glass (except the extreme edges) or smoke spilling into the living area.

I believe 15' is mentioned in most as it pretty much covers most situations. Here's what I learned about draft so I could figure out what I could do to improve mine. The chimney height helps draft, the more surface area the more it sucks your draft. A short chimney doesn't have a lot of surface area so it doesn't have as powerful a draft.

Since draft is determined by temperature differences between inside & outside, the warmer it is outside the more powerful your draft needs to be to overcome it. That's to say a short chimney since it has less power will have more problems trying to have a fire going when it's warmer outside vs. a longer one. You'll probably experience this after you get your insert installed you'll want to light it off and see how it does when it's 65F outside and find it difficult, maybe impossible and your glass dirties up. There's a certain temperature outside you'll eventually find where you simply can't get draft. I've lit a fire in my insert at 58F outside since I redid my install and was able to do it, it was previously impossible unless 45F or less outside.

Inside chimneys draft better than outside (in part they're already warm, and outside chimneys can be reverse drafting when not in use).

Outside environmental influences play. I live in New England, and find those cold foggy thick days it's hard to get a draft going, like there's heavy air above your house that won't let smoke through. I can tell those days when I start a fire and the smoke comes out my chimney then spreads horizontally unable to penetrate this "barrier" above my house. The smoke sort of makes a cloud above my, and my neighbors houses instead of flying up and away (until secondary burn gets going). Those days it takes a bit more babysitting. On real bad days the smoke comes out my chimney and falls to the ground. Once secondary burn gets going, there is no more smoke so you don't see it anymore.

Flex pipe restricts draft more than rigid, Insulated pipe heats up hotter than non-insulated giving stronger draft, bends interfere with draft so the longer your straight run the more draft you'll have.

Case in point, a 12' insulated, internal chimney, straight run, rigid pipe, not ovalized will draft better than a 15' flex run, with a couple bends, ovalized, on a exterior. Also, I believe the closer you are to sea level the better your draft. Those in Colorado as I understand should err on longer runs.

So, you may not need 15' but will find your experience and enjoyment better. That part that sticks out of your chimney if longer than 4" or so needs to be insulated else it'll hinder your draft more than help. If not insulated it'll rapidly cool the exhaust down causing creosote to form and slowing down the exhaust at the end, causes a slowdown in the whole system. To extend my chimney I continued the single-wall stainless 4' out of my chimney, did the storm collar & sealing, then insulated the part sticking above with kaowool, and protected the whole thing from the elements with an extend-a-flue.
 
I'll count myself lucky on the draft issues. It was 80deg when I did my first beak in fire and had just minor smoke spillage into the room and the fire lit right up! :p
 
I started out by ovalizing mine, but then decided to cut the damper. I am quite fussy and had difficulty getting the liner perfectly round again. So I marked it with a sharpie, pushed the liner up out of the damper and made the cuts. A 4" angle grinder with a cutting wheel only takes a couple minutes. Then put a grinding wheel back on it and smooth out the sharp edges. I had enough extra liner to pull a couple feet through the damper and cut it off again. Leave the pieces in the back of the fireplace incase anyone would ever want to go back to a standard fireplace. A good welder could weld them back in. I can't imagine that ever happening after having an efficient insert in there though.
 
Thanks for the insights! I'm definately committed to cutting out the damper piece since the cutting has begun! I will be running extra rigid pipe above chimney along with insulation. I don't want to be outside in the winter trying to make improvements. Hope to post a picture once the job is complete. Thanks again for sound advice.
 

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One suggestion, look for a ridgid piece compatible with your system that is double wall pre-insulated. I think it will looks nicer than trying to use single wall and just wrapping insulation around it. Maybe Hog has some pics?
 
Twelve feet might work for you IF you are using rigid liner w/ few or no bends - some folks do rigid in the chimney with 4-5' of flex at the end to make the connection to the insert, which should also work fine. It will also help to have an inside chimney, and to insulate the liner. This will give an optimal setup aside from the height, and may make up for the "works everywhere" 15' generic listing. However your code official might insist on the 15' minimum - some do, some don't... In either case it won't hurt to have the extra, as long as you insulate the extension as mentioned earlier.

Also looking at your picture, you might need to think about extending your hearth - remember that current requirements are for 18" in front of loading doors, doesn't look to me like you'd have anything near that, and the hearth rug does NOT meet the requirement. It would be possible to extend by taking up an area of the wood flooring, and possibly part of the subfloor, then building back up with non-combustibles to the required minimum R-value and covering with stone or tile to have something flush with the floor.

Gooserider
 
Gooserider & Co.

Appreciate the insights. I ran the flex liner already and have plenty of extra liner. I am using rigid liner at the top of the chimney to support the flex liner that I will run up thru the rigid to get 15' and will look for the double walled rigid liner. If it's double walled do you need to insulate it, especially if I'm running the flex inside of it? If so what is the advantage of using double walled liner? The photo is old and after the insert is installed the chair, books, and hearth rug will be removed and a hearth pad will be put in place. Is there such a thing as a soapstone hearth pad. I have a friend that has a marble fabrication shop and he could give me a good deal on an 18" scrap piece.
 
If you are running the liner inside the rigid, you just made your own double wall. Just make sure you insulate the liner before sticking it through the rigid piece.
 
How do you insulate the liner prior to insertion. What do I use.....some type of insulation wrap? My flex liner is 6" and the rigid is 7". Does this leave enough room?
Thanks
dan
 
Log-a-rhythm said:
How do you insulate the liner prior to insertion. What do I use.....some type of insulation wrap? My flex liner is 6" and the rigid is 7". Does this leave enough room?
Thanks
dan

Dan what kind of rigid pipe are you using?
 
I was told I didn't need to use stainless because I'm running the liner into the rigid. So I was planning on using 7" galvanized sheet metal hvac pipe. Sound good?
 
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