Hi, should the inside of a cinder block chimney have some type of insulation? The chimney measures 16x32 inches on the inside with 7x11 inch clay tile liner (running pretty much up the center) and a sheet metal chimney cap. Also the chimney is 13 feet tall to the top of the wood burner. Thanks

Looks like we need to start with the basics here, a chimney should never be build from cinder block or even concrete block. That being said, you have one so lets start from there. No insulation needed but make sure the clay liner is intact. Cinder block has not be made in the US for decades so we'll assume you mean concrete or cement block. This stuff leaks and wicks water and will crack/slit if exposed to water and freezing temps. Where do you live and how's your climate?

I think he means cement block hopefully. This may be the by product results form one of those DYI shows or even Holmes and Holmes and to many shows that use the word "Cinder" block and they obviously don't' have a CLUE what a block is made of. Personally one of these days I need to tell them this. What a poor research the show has when they don't even know what the block is called. Many times they will even call a cement block a cinder brick! What idiots
Sorry parttime
Lets check the chimney height it should be 2 foot above any object 10 foot in radius. You have a very cold chimney and its really a highly susceptible chimney for fire. That chimney will be way to cold if there is a air tight stove hooked to it. They actually make Insulated chimney block since the last 25 years. Reg chinner block is basically for a furnace/boiler exhaust. Not for a wood stove so we thought in the 70s wood stove boom. YEP Ive ripped enough of those down before because the chimney gets to cold and the flue gas take to long to reach the top and cools and actually 'rains" in the chimney when it goes to shut down. You can tell that by looking at 1/4 down from the top and if you see black soot at the mortar joints then there is a serious problem. Thats condensation mixing with creosote and bleeding through the block and block joints. If this get to wet and freezes the flue and block joint will freeze and split. Now the flue joint will keep getting worse and let gas escape between the flue and block and then is where the fire eventually starts. The other problem I see if the wood stove has a 6" exhaust to the chimney the flue is TOO big. We call them a 8x12 in the trade. If the stove is even 8' exhaust the chimney is still to big. Gees I can use a 8x12 flue on a standard 36" fireplace with a 27" high opening. By the flue being so big the flue gas semi stall in draft. Its like putting a house floor fan in a gym and expecting it to move air to the other side. The old days they thought bigger is better wood stoves and did not really take time to understand the Mechanics in fossil flue gas. This is coming from a mason of 30+ years and not something I read. So check the chimney and once a week keep it wide open a day to help crystallize the creosote built and turn that into an into a inert stage
here is some info on chimneys I just found and still some things are missing in it but gives a good general outline

Chimney draft: how to diagnose and repair chimneys with inadequate draft and smoky fireplaces.


Signed 21 Boat

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Ballenger, l live in southern wv, and it's been real cold this last week.
Boat, you guys are right about the blocks, I've concrete. The woodburning stove connected to chimney works fantastic, great heat, no smoke in the house, and easiest I've ever seen to start a fire. What brought about the question, l am seeing some discoloration at the seams of the concrete blocks. I was wondering if that space between the clay liner and blocks had some type of insulation would eliminate this staining? If so what could I use? Thanks again for the help, you guys are great.

Balengerb1 The NEVER build a chimney from concrete block is incorrect.
I'm not sure what you do in your neck of the woods for a chimney for a boiler or a wood stove to put up a chimney? I guess its all brick or the SS chimneys ouch!
Especially when it comes to a boiler needs a chimney. Must be the 'hoffa" thing :D

Our Concrete chimney block is for rectangle flues or square flues. Is a 16x16 concrete block or a 16x20 concrete block. These both come insulated or non since the 80s here. The reason Balengber1 came up with the never is because nobody understands the fossil fuel chimney to begin with just read the sites and the problems with them. How about if I told you I put up a chimney in 1976 and went to clean it for the first time in 1981 and it was a waste to get my chimney brushes out. The flues were CLEAN all the way to the first flue set. I got a Dixie cup of dust out of the clean out door. This was a frontier stove that solely heated the house.

Our block plant make thousands a week here. As A matter of fact my town in the 70s was used as a pilot program for the state of PA as to set new state codes and NFPA codes. I was fortunate to be a part of that. Thats also was when the Stainless Steel chimneys were coming out of double and triple walled to insulate the chimney. I was doing chimney sweeping back then I noticed the Inner walls of the double and triple walls were corroding. I contacted the manufacture and my supplier and told them I noticed the ones that were going bad had wood coal combustibles using them and the worst was the all coal burners. The coal produced acidic acid witch ate the Stainless Steel out. Hart and Cooley along with all major manufactures were mandated by state and the feds in the quality and concentration of the Stainless Steel Chimney. It was so wild back then that a WHOLE county was banned here for any fossil fuel stoves to be put up. The insurance companies were also involved in this. I also brought to the counties inspectors that I had 1 year old 8" crocks that some of them cracked on the 6" stoves. I had a 8' clay crock with 8' of masonry around it with a 1' air space to any combustibles. I relayed the crocks and wrapped them with SS flashing to provide that micro expansion of the clay crock to get jammed in expansion and crack.

As a mason I will never forget in 1979 I personally laid up over 60 chimneys in that year alone It was so strong here I couldn't get Concrete chimney blocks at any of our 3 major block plants nor in upper Maryland

Sorry more history on the misunderstood concrete block chimneys

Parttime If you re read my first post and the quote above I mentioned the Soot staining the block joints and about where it shoes up on the chimney. Your chimney is to cold at the last 1/4 or 1/3 of the chimney. Typically this is where it stains the block joints.
Give me very accurate details on what your stove metal smoke pipe is. How you burn the stove heavy or bank down the inflow of air. How much adjustments it has on air. How you have your damper in the smoke pipe if you have one. What the manufacture of the stove is. Is there an ash pit below the crock with a clean out door on the outside of the chimney. How often do you burn the stove and do you let it cool down and re fire in the morning? I need EVERY detail to try and fix your chimney problem and worst case scenario is it needs taken down. The 8 x12 flue is completely to big for the stove like I mentioned in my first post. Is this chimney just for the wood stove? What is the OUTSIDE measurements? You mentioned 16x32 inside. Is there another 8"flue in there for a boiler?
Which would be 4"blockside12"flue4"centerblock to separate the next8"flue4"block side. Which is a chimney 16 out from the side and 32"wide Outside. So how did you get 32"inside?

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Boat, thanks again for help, loved the little history on blocks.

I sure didn't know this was so exacting, I'll try and give you the best info I can, I also have one photo that might help, I'll try and send it.

Here goes: first it's a wood burning fireplace insert not a stove as I referred to it originally. It has no name or model tag on it, it was in the house when I bought it in 1991. I use it around the clock when it's cold, reducing the air intake and closing the damper a little at night and I only let the fire die down a little to clean out ashes, it has no clean out on the chimney so I use the bucket method for ashes. I only burn seasoned hard wood. I just measured the outside of chimney it's 32"X56", which gives an inside measurement of 16"x40" ( I think) with the 7"x11" clay flue tiles coming up the middle. The pic I'm going to try and send is of my son inside when we replaced the tile because of a crack in the old tile, replaced all the tiles at that time.
The insert has a rectangluar metal connector that slides up inside the clay flue tiles about 8" and bolts to the heater. I hope I answered all questions. Thanks again

Parttime It is a fairly exact science as I mentioned early and why all the blogs on cement block chimneys. A lot of the Exact science can't put in print is because it's the intelligent mason that knows by life's experiences. Even that is not always working. The masons weren't the chimney sweeps to see how it went and the chimney sweeps didn't build the chimneys. I personally never saw a mason that was a chimney sweep nor vice a versa except me. The engineered could only state basic science of heat and drafts. There are to many variables for them to get a handle on and the different ways of adjusting air flow into the chimney This is way more complicated then sewer venting.
Oh so it's a fireplace insert which changes the whole picture and brings up a whole another hosts of issues.
Is this a basic 36" fireplace that the finished opening in the house would be about 34"wide by 27 to 29" high? The 8x12 flue basically dictates its a standard 36 and not a 48" fireplace if it was done right in the first place.
Was there a damper laying around somewhere that was pulled out to install the insert or was it left in wide open and the insert pipe was shoved in the corbeled brick throat inside?
You have a very good set up as far as the flue in relation to 8" of masonry to combustibles. You still haven't answered me on where the soot stains on the chimney is. This will give me some answers as to how bad of a rain forest you have in the chimney flue? Did you ever pull the insert to clean out the smoke shelf behind where the damper was and the corbbled brick throat above the damper where the first flue would sit.
When you went to reline the flues was there a throat above the damper?
So next set of questions
1. Did you ever pull the insert to clean and check the fireplace throat out and how did that look inside.
2. Did you see at all a shiny black sheen of tar like soot hanging looking like little stalactite's?
3. Is the fireplace all in the house and only the upper chimney through the roof exposed to the out side, or is the back of the fireplace exposed to the outside?
4.When you relined the chimney was there a fireplace throat below the first set flue.
5. The picture you showed me was all of this space just for the 8x12 flue and not a furnace flue?
6. If and when you pulled the insert out did you happen to see a little flip door on the bottom of the firebox it would be about 4"x6" plate?
7. Still waiting on where the stain/soot on the block joints are located on the chimney?
I was on another post answering a question about a homemade wood stove in a shop and everybody freaked out and stated it probably didn't have a UL listing not approved etc. And yet to date the most dangerous fossil burning device is a fireplace UL NFPA approved insert in a fireplace and can be very dangerous if not handled right. The manufactures across this country get there product approved to Gov specks but NO ONE has a freaking clue the danger is in the throat of the actual fireplace and then the flues. And there Are no real precise written specks for that end of the whole system and how it really works. The fireman keep putting them out and all they say is the chimney needed clean. Ha.
Don't panic. We can get this to work for you but I need some answers. It may be a pain but it can work. I'm the only person that I know of that built a fireplace inside a walk in fireplace that worked fine on a very old farm house. It was fine until the put all new windows in. I was only 21 then. Ha. The best one is I did set a piece of glass by the first flue in a fireplace and completed the job and I felt I was going to get stung by the customer. So when He went to fire it up it smoked. He looked up the throat and couldn't see the glass blocking the draft. I made a deal and said the day I get cash in hand I will fix the fireplace to work It takes a brick down the chimney and now a little cleanup of the smoke shelf and bingo draft.
A little more history of the masonry world which is a dying breed and I'm one the last of its kind in age. A real mason not a young kid or a Million Mexicans building like Mexico. No offense but what do they know about a fireplace of the 19th centurary let alone the 30 year old Americono.



Signed 21 Boat

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I'll try to answer your questions in the order you ask:
the fireplace measures 36"x27". The chimney was built for the insert, it's wide open and the damper is inside the insert. The soot stain starts about a foot from the top of the chimney. I tried to take a pic, but with the sky background it was to dark. I had the insert out when I relined it, the throat was clean. I'm not sure what you with "corbbled brick throat.
next set of questions:
#1. did have insert out, looked clean
#2. No shiny black sheen anywhere.
#3.the fireplace is built on an outside wall, the back is to the weather.
#4. the first flue starts level with the top of the opening for the insert, so I say no fireplace throat below the first set flue.
#5. The only thing in the chimney is the 7"X11" clay flue tiles. That space is what I thought should have insulation?
#6. No flip door on the bottom, solid concrete
#7.The stain is about the first block from the top of the chimney. I'll try to get a pic tonite.
I'll not panic, we can do this,"Yes we can". Oh yeah, I loved the little glass trick, a man got to do what a man got to do. I guess you got your money?

Would it help the insulate the area around the flue? Thanks

Boat here's a pic, if you can make anything of it.

partttime . The flue in there now, What was the rest of the void filled with around the flue?

By the pic your chimney is getting beat up on the spark arrestor and condition of cold to warm air mas creating a rain cloud.
You have serious drippsy! The best chimney is mass to remain hot.
Your combo here is the flue should have been and 8x8 flue unless you have a massive exaust on the insert. Your not getting enough hot air flow up and out the chimney in relation to the wood stove being banked down to low intake of air flow. The stove pipe connected to the bottom flue, how was that done? Is there any portion of the flue below where the stove connects
Here are some options. You need to get another adjustable air supply into the chimney to make up for the stove being banked down so the gas while still be hot or fairly warm to get OUT of the chimney before it wants to condensate.The spark arrestor doesn't/t help but it may be code in your area.
NOTE: spark arresters were originally designed for fireplaces and how many of those burned down a house in the last 200 years. The most common fireplace fires is because the fireplace screen wasn't put in front of the actual fireplace
If the chimney catches fire because of creosote its goes like a freight train and MELTS the spark arrestor and while that freight train is going the spark arrestor actually defeats the sparks TOO the roof below and doesn't allow the hot gas to go higher in the air. Take a piece of plywood over a camp fire and a stick to disturb the fire and SEE where the sparks GO sideways and to the ground to your feet. Go figure basic science. Again our society pushing sales against what BASIC science shows differently
explain the 'gap" your are talking about to fill with insul.
remedies
1. Smaller 8x8 flue
2. Remove spark arrestor If code allows ( I personally get rid of it) Your choice
3. Need an auxiliary air supply for big flue
4. cut through back of chimney from outside below crocked in pipe from stove for ash clean out and allow more air in chimney form clean out door not being air sight.
5. Is void in chimney fill in with more block and perlite insul fill be twee block to block wall inside of chimney.
6. rig up a possible air flow inside side of insert and below crocked stove location.
7 "standard" Bun stove full open in draft once a week to really heat up the flue and dry out the whole chimney itself and to insure dangerous creosote is naturalized and turned to ash.
Note a higher chimney will improve draft but become a Moot point since the stove controls the gas speed in the flow of the chimney.
So get back on the inside fill and location of the areas I need to know please.
Sorry for the wait I got hung up here.

Boat, The void iside the chimney around the flue has nothing in it, that was the area I was asking about putting some kind of insulation. You mentioned Perlite, what is that?
Smaller flue is not really and option right now, insert drafts great now.
Spark arrestor will come off today
I'll see what I can do for additional air intake
I burn stove wide open at least once a day.

Ok, I just read a little about Perlite insulation, that's what I was wanting to find out about, didn't think that area of the chimney should be left empty. Thanks again

Wow that's your problem. I never would have imagined putting up that chimney without masonry fill around the flue at all Never!
You don't want perlite touching the flue. I your situation perlite would have been perfect to be poured in the block cores that are laid there now and then block fill around the flue It comes in bags and pours real well in many courses of block (2 core) that are laid up. You can pour it in 8 foot lifts ( block wall height sections)
Who originally built this?
How does the flues stay in place??
No my other concern here is if the flues are just floating in there and since there is NO protection in mass that the flue joints have now hair line cracks in them from freezing. What did you do for the wash/mortar cap st the top. Obviously there has to be something for the soot to come down and over the outside flue.
Perlite has been used as insulation in open block cores in commercial buildings since I was a kid in the trades in the 70s. We used to use vermiculite but that compacted after a while and now we find out it may contain some asbestos. Perlit is used for so many banine applications and is relative safe and can take some heavy heat.
Check with your commercial insl companies and call the masonry supply house the can help direct you or a BIG mason contractor. Perlite is a generic name.
I posted a good website to direct you and the specks on it and where its mined
Get back on that.
Perlite Institute, Inc.
www.perlite.net

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I made the cap for the chimney out of sheet metal, it can be removed. So your saying there's no insulating material that I could fill that void with, that could come in contact with the flue tiles?

Correct no insul directly against the flue. And the flues need block around them to hold them in place. A perfect way to insulate this is take that metal cap of Inspect the flue liners mortar joints. I could just about guarantee they have hairline cracks in them. The main objective is to stead the flues from falling over wow.
To do this right tap flues off and out of chimney save good flues. Lay block around for the flue opening and build that up inside three courses. You can lay them and stand on the fresh laid block just try to keep the wobbles out. Lay three courses up and pour in the perlite in the hollow cores. Now set the 24"flue where you left open inside thoes three courses Repeat that.
I know you want so badly to lower block in from the top but bumping a flue and braking its mortar joint loose could be real easy to screw that up.
personally this is when I would go to a 8x8 flue. Think about I don't know how big the exhaust is on the stove but a better matched flue would send the gas up quicker and keep the chimney warmer. Its up to you. By size to size match is what its all about.
Either way the flues need masonry support. And mass or mass with insul around it to keep the chimney warm.
I know it's a pain.
How was the stove insert hooked to first flue? And how much drop if any would be below the crocked tie in. If there is several inches the you Cord come in from the outside block and use a 6' round crock mortared below the crocked insert pipe and the ash pit in the flue can be accessed from the outside.
What Size is the pipe coming off the stove into chimney?
What is you Geo location so I can get as Idea of how could it gets there?

The pipe coming off the stove is just shy of the 7"x11" flue tiles, it slides up into the flue tile and temporarily secure it, then you slide the insert in and line it up, remove temporary hook and slide it on top of insert and install four bolt, 3/8 I think. I live in southern West Virginia

If That's the size of the stove pipe then stick with the 8x12 flues great match!

OK

Happy burning!
I've never tried this product before but once you get it all done and all is good try this possibly for the stain removal

http://www.greenwoodusa.com/Tech_Doc...te_Cleanup.pdf

Or just pressure wash it and make sure it real clean and a scratch coat and finish coat of stucco and it can go on bare clean block no wire required.