Does an interior masonry chimney stay as hot inside as a metal one?

[MI Feller]

Planning to take down an old metal thru the attic and replace with new interior masonry. New one will run up to a cathedral ceiling eliminating need to go through attic. Will be block with a fake brick covering for appearance. Seriously looking at SS liner. Anyways, came upon interesting article which said that in masonry, you don't have the insulation present that most metal chimneys contain and that the entire masonry structure acts like a "heat sink." Made me wonder if the flue temp stays as hot, which is desirable to keep creosote down. One more question, if the block is properly installed using the right mortar should I be worried about any deterioration above roof over next 10 years? Also would it hurt/help if the above roof section is also covered with a brick like facing? Thank you for any ideas.

 

[Rob From Wisconsin]

We have an interior masonry flue, and the only reservations I have
on it are it is that its diameter may be a bit too big - I may re-line it.
Otherwise, it's good. After several hours, it begins to throw-back heat
into the house (a secondary heat source), and being that it is interior,
it always drafts pretty good, even from a "cold" start.

 

[Dave_1]

Does an interior masonry chimney stay as hot inside as a metal one? ... Made me wonder if the flue temp stays as hot, which is desirable to keep creosote down. One more question, if the block is properly installed using the right mortar should I be worried about any deterioration above roof over next 10 years? Also would it hurt/help if the above roof section is also covered with a brick like facing? Thank you for any ideas.

Does an interior masonry chimney stay as hot inside as a metal one? - No, there will be more ash / creosote build up in a masonry chimney.

So while deterioration will began it will take longer than 10 years for such to become a problem.

Good luck with it

 

[oldspark]

Does an interior masonry chimney stay as hot inside as a metal one? ... Made me wonder if the flue temp stays as hot, which is desirable to keep creosote down. One more question, if the block is properly installed using the right mortar should I be worried about any deterioration above roof over next 10 years? Also would it hurt/help if the above roof section is also covered with a brick like facing? Thank you for any ideas.

Does an interior masonry chimney stay as hot inside as a metal one? - No, there will be more ash / creosote build up in a masonry chimney.

So while deterioration will began it will take longer than 10 years for such to become a problem.

Good luck with it

I think there is more to it than a yes or no answer, what type of metal chimney vs what type of masonry chimney, if the block chimney is done right it will give you many years of service with out any problems as well as a metal chimney.

 

[Dave_1]

Does an interior masonry chimney stay as hot inside as a metal one? ... Made me wonder if the flue temp stays as hot, which is desirable to keep creosote down. One more question, if the block is properly installed using the right mortar should I be worried about any deterioration above roof over next 10 years? Also would it hurt/help if the above roof section is also covered with a brick like facing? Thank you for any ideas.

Does an interior masonry chimney stay as hot inside as a metal one? - No, there will be more ash / creosote build up in a masonry chimney.

So while deterioration will began it will take longer than 10 years for such to become a problem.

Good luck with it

I think there is more to it than a yes or no answer, what type of metal chimney vs what type of masonry chimney, if the block chimney is done right it will give you many years of service with out any problems as well as a metal chimney.

Read the op's question & the answer given again.

It was not stated or implied that a metal chimney was superior to a masonry chimney.

Deterioration, whether in metal or masonry, is the result of burning procedure & cleaning practices. The drier the wood, the more frequent the sweeps, etc the longer it will take either chimney to deteriorate.

 

[Highbeam]

I understood the question a little differently. The inside of the metal chimney will GET hot more quickly which is the most important thing to minimize creosote build up since it is during the cold start phase that the fire is puking lots of pollutants and a cold flue is where they will accumulate. The masonry will stay colder longer and so will condense more junk out of the colder fire's smoke. Once both are up to temp, the masonry will stay warmer longer. Don't be confused by the masonry's ability to retain some heat via thermal mass, that is not the same as the flue staying hot enough to prevent creo from forming with the next fire. It'll just be warm vs. room temp with the steel.

Due to the conductive properties of masonry, the masonry chimney will be a greater heat sink than the steel pipe so I believe that you will experience more creosote with a masonry vs. an insulated steel flue.

Why on earth would you build a masonry chimney with all it's flaws and then line it to try and gain back the performance of a steel flue by lining it? Have you considered boxing in a regular steel flue and applying your brick veneer to this chase? I understand the aesthetics of masonry are superior to a pipe but you can have both since you're veneering it anyway.

 

[oldspark]

I understood the question a little differently. The inside of the metal chimney will GET hot more quickly which is the most important thing to minimize creosote build up since it is during the cold start phase that the fire is puking lots of pollutants and a cold flue is where they will accumulate. The masonry will stay colder longer and so will condense more junk out of the colder fire's smoke. Once both are up to temp, the masonry will stay warmer longer. Don't be confused by the masonry's ability to retain some heat via thermal mass, that is not the same as the flue staying hot enough to prevent creo from forming with the next fire. It'll just be warm vs. room temp with the steel.

Due to the conductive properties of masonry, the masonry chimney will be a greater heat sink than the steel pipe so I believe that you will experience more creosote with a masonry vs. an insulated steel flue.

Why on earth would you build a masonry chimney with all it's flaws and then line it to try and gain back the performance of a steel flue by lining it? Have you considered boxing in a regular steel flue and applying your brick veneer to this chase? I understand the aesthetics of masonry are superior to a pipe but you can have both since you're veneering it anyway.

So metal chimneys are better with out a doubt in every case?

 

[dvellone]

As a professional Stonemason I've built many masonry chimneys and am intimate with their design and performance. I'm always astonished at the attitudes toward masonry chimneys, and in particular the comparisons between masonry and steel. Masonry chimneys have gotten a bad rap primarily from the fact that, unlike an insulated steel chimney which is built to exact specs in a controlled environment on an assembly line, they are custom constructed one at a time and are only as high in quality (and performance) as the Mason's skill allows. The many incorrectly designed and poorly built masonry chimneys unfortunately have set the standard used when comparisons are drawn with insulated steel. The fact is that a correctly designed and constructed masonry chimney will provide as good a draft as steel ( if not stronger) and will build up no more creosote than steel will. Some of the most critical design features are that: the chimney would be constructed inside the house; properly sized round ceramic tiles rather than rectangular or square are used; and the entirety of the clay liner is separated from the outer masonry by a space that is filled with insulation. There are numerous other requirements relating to the integrity of the masonry construction itself, but these are the factors most important to the chimneys function, and those that when ignored will severely limit the chimney's performance. Ceramic flue tiles won't build up creosote more rapidly at start up than steel will if the two are within the home and at the same temperature. The tiles heat quite rapidly, retain their heat much better than steel, and when properly insulated the masonry construction will not act as a heat sink drawing critical draft temperature away from the flue. Ceramic tiles are also not affected by the corrosive products of combustion which ultimately will degrade metal flues resulting in a much shorter life span than the tiles'.
As I've said before, insulated steel chimneys are a great and high quality product. They are simple in their design, take up a limited space and require none of the sub-structure, mass, and time and money that a masonry chimney requires. You can put up a safe and quality chimney on a weekend and not break the bank. I have one venting my castine. It was sensible given my space here and my investment limits in my cabin.

If you want to compare the two though for your own decision you need to compare them in terms of your aesthetic desires and architecture of your home. In terms of performance (and proper construction) you'll be pleased with both. If you want to save time and money (and your back) you'll use steel. If you're into the look of masonry and you have the time, patience, skills, and enjoy building impressive structures you'll go with masonry.

 

[Highbeam]

I understood the question a little differently. The inside of the metal chimney will GET hot more quickly which is the most important thing to minimize creosote build up since it is during the cold start phase that the fire is puking lots of pollutants and a cold flue is where they will accumulate. The masonry will stay colder longer and so will condense more junk out of the colder fire's smoke. Once both are up to temp, the masonry will stay warmer longer. Don't be confused by the masonry's ability to retain some heat via thermal mass, that is not the same as the flue staying hot enough to prevent creo from forming with the next fire. It'll just be warm vs. room temp with the steel.

Due to the conductive properties of masonry, the masonry chimney will be a greater heat sink than the steel pipe so I believe that you will experience more creosote with a masonry vs. an insulated steel flue.

Why on earth would you build a masonry chimney with all it's flaws and then line it to try and gain back the performance of a steel flue by lining it? Have you considered boxing in a regular steel flue and applying your brick veneer to this chase? I understand the aesthetics of masonry are superior to a pipe but you can have both since you're veneering it anyway.

So metal chimneys are better with out a doubt in every case?

It's not so simple. What is "better" to you? I tore down a masonry chimney to install a steel chimney and everything is better. I can only see two benefits to masonry, the aesthetics of masonry though a good mason can make a chase look pretty good, and the thermal mass properties which really depend on design and is a double edged sword. I prefer the thermal mass in the stove.

Sure if both flue materials (clay and steel) are at the same temp then they both accept creosote at the same rate. The difference is in how quickly they heat up to operating temp where creo won't form. The clay flue liners are quite thick compared to the very thin stainless steel (pretty non-corrosive) material of a steel flue. Is it not obvious that the thin steel will rise in temp much faster than a very thick (like 20x as thick) clay layer?

So what do you think Oldspark? Is there ever a time when masonry is a better building material? It's not in cost, it's not earthquake stability, it's not in flue temps, it's not as leakproof, it's not in maintenance. I would have a hard time recommending a masonry chimney built by even the best mason to my mother or anyone else.

 

[oldspark]

Nice post dvellone and my thoughts exactly, I have a 30 year old masonary chimney with a 7 1/4 inch round liner with insulation around it and it has always served me well, it now needs some TLC and hope to have that done this summer.

 

[oldspark]

I understood the question a little differently. The inside of the metal chimney will GET hot more quickly which is the most important thing to minimize creosote build up since it is during the cold start phase that the fire is puking lots of pollutants and a cold flue is where they will accumulate. The masonry will stay colder longer and so will condense more junk out of the colder fire's smoke. Once both are up to temp, the masonry will stay warmer longer. Don't be confused by the masonry's ability to retain some heat via thermal mass, that is not the same as the flue staying hot enough to prevent creo from forming with the next fire. It'll just be warm vs. room temp with the steel.

Due to the conductive properties of masonry, the masonry chimney will be a greater heat sink than the steel pipe so I believe that you will experience more creosote with a masonry vs. an insulated steel flue.

Why on earth would you build a masonry chimney with all it's flaws and then line it to try and gain back the performance of a steel flue by lining it? Have you considered boxing in a regular steel flue and applying your brick veneer to this chase? I understand the aesthetics of masonry are superior to a pipe but you can have both since you're veneering it anyway.

So metal chimneys are better with out a doubt in every case?

It's not so simple. What is "better" to you? I tore down a masonry chimney to install a steel chimney and everything is better. I can only see two benefits to masonry, the aesthetics of masonry though a good mason can make a chase look pretty good, and the thermal mass properties which really depend on design and is a double edged sword. I prefer the thermal mass in the stove.

So what do you think Oldspark? Is there ever a time when masonry is a better building material? It's not in cost, it's not earthquake stability, it's not in flue temps, it's not as leakproof, it's not in maintenance. I would have a hard time recommending a masonry chimney to my mother or anyone else.

I was just asking and looking for views on the subject with the OP in mind.

 

[dvellone]

It's not so simple. What is "better" to you? I tore down a masonry chimney to install a steel chimney and everything is better. I can only see two benefits to masonry, the aesthetics of masonry though a good mason can make a chase look pretty good, and the thermal mass properties which really depend on design and is a double edged sword. I prefer the thermal mass in the stove.

Sure if both flue materials (clay and steel) are at the same temp then they both accept creosote at the same rate. The difference is in how quickly they heat up to operating temp where creo won't form. The clay flue liners are quite thick compared to the very thin stainless steel (pretty non-corrosive) material of a steel flue. Is it not obvious that the thin steel will rise in temp much faster than a very thick (like 20x as thick) clay layer?

So what do you think Oldspark? Is there ever a time when masonry is a better building material? It's not in cost, it's not earthquake stability, it's not in flue temps, it's not as leakproof, it's not in maintenance. I would have a hard time recommending a masonry chimney built by even the best mason to my mother or anyone else.

In terms of cost to lifespan its pretty hard to not recognize masonry as being advantageous. I think most of us in the construction field would say that masonry is a better material in that regard and that is a factor in its cost that does deter it's use. But most of us aren't concerned with longevity in construction. We're more of a disposable society putting up tract houses in remarkably short times.
Flue temps? Based on the chimneys I've built I'd say that the masonry has to be just fine in this regard. Your old chimney? How was it built?
And I have to disagree strongly as far as leakproof goes. Properly built and flashed a masonry chimney will not leak. Look at all the masonry structures in cities that continue to be built. That statement flies in the face of tried and true construction practices. In fact only 24% of the worlds 100 tallest buildings contain a purely steel structure. The rest, including Burj Khalifa the current tallest building are built with composite or reinforced concrete which is much more prevalent. By the way that 24% is down from 57% in 1990 so the newest and tallest structures are using more concrete. Reinforced concrete also does pretty well in earthquake zones when that is taken into consideration.
By the time you'd even need to consider repointing a well built masonry chimney (only above roofline) you'd have replaced at least one if not two steel chimneys. Maintenance aside from regular flue cleaning or flashing checks is nil for many, many years. With all due respect, if you can only see two benefits to masonry construction chances are you're not seeing the whole picture or have a certain amount of bias based on experience with poor masonry construction.

 

[vvvv]

Something to consider is the boiling point of water which is 212*f so if the chimney stays above 212*f the water won't condense?

 

[Highbeam]

Please, comparing a reinforced concrete skyscraper to a pile of concrete block and mortar is hardly apples to apples. You ought to know that masonry construction is not the same as reinforced concrete construction. Masonry chimneys are known to fail in earthquakes, tip and crack, they are known to be very likely to leak through either the crown the flashing or even the mortar joints. This last one that I knocked down had cracked liners, cracked masonry block on the rear of the fireplace, and plenty of rot damage to the wood framing around the chimney due to water leaks. I suppose I do have a bias due to my bad experience and also I am a civil engineer, they teach us about masonry construction.

Longevity is a funny thing. The lifespan for a steel system is not expected to be nearly as long as the lifespan of the best masonry chimneys. So yes, you would conceivably have to pop in a new steel pipe after 20(?) years. Ever notice how many folks are lining their masonry chimneys to resolve the issue of a cracked flue liner?

To avoid the pretty much guaranteed 20-30 year steel replacement you could install a masonry chimney and hope that you find the rare good mason to build it for you at great cost, you would also have to live with the mild inferiorities of the masonry system for those 20 years. Of course who lives in the same house for 20 years anymore? I thought the average was 7 years.

I do appreciate good masonry work but when the average mason builds a chimney, well, it is almost never that good. At best you can hope it lasts longer than a steel pipe.

 

[dvellone]

Please, comparing a reinforced concrete skyscraper to a pile of concrete block and mortar is hardly apples to apples. You ought to know that masonry construction is not the same as reinforced concrete construction. Masonry chimneys are known to fail in earthquakes, tip and crack, they are known to be very likely to leak through either the crown the flashing or even the mortar joints. This last one that I knocked down had cracked liners, cracked masonry block on the rear of the fireplace, and plenty of rot damage to the wood framing around the chimney due to water leaks. I suppose I do have a bias due to my bad experience and also I am a civil engineer, they teach us about masonry construction.

Longevity is a funny thing. The lifespan for a steel system is not expected to be nearly as long as the lifespan of the best masonry chimneys. So yes, you would conceivably have to pop in a new steel pipe after 20(?) years. Ever notice how many folks are lining their masonry chimneys to resolve the issue of a cracked flue liner?

To avoid the pretty much guaranteed 20-30 year steel replacement you could install a masonry chimney and hope that you find the rare good mason to build it for you at great cost, you would also have to live with the mild inferiorities of the masonry system for those 20 years. Of course who lives in the same house for 20 years anymore? I thought the average was 7 years.

I do appreciate good masonry work but when the average mason builds a chimney, well, it is almost never that good. At best you can hope it lasts longer than a steel pipe.

The OP lives in Michigan. I'd hardly think he has much concern about earthquakes. And as far as masonry chimneys known to tip, crack, and be very likely to leak through, anything poorly constructed will suffer in it's integrity. To continually point out the worst case scenario while ignoring the quality of proper constructed masonry chimneys does little to offer the OP some informative input on the subject. You're bias is clearly evident and I'm genuinely surprised that as a Civil Engineer that that is all you can pass on. Seems that there are posters here that need to expound on every subject regardless of the depth of their knowledge. Help the poster with facts if you can or leave it alone. Does an interior masonry chimney stay as hot as a metal one? Yes. it will certainly stay as hot as a metal chimney. And the heat will be more consistent throughout the burn cycle.

 

[Dave_1]

Hi MI Feller,

consider this fwiw

Concerned about my then 25 year old Metalbestos chimney I called Selkirk & asked for the average life expectancy.

Was told that they did not have such stats but had heard of customers with 35 years & still going strong.

In a metal chimney the last section before the rain cap is where the corrosion buildup is usually the worse.

So I swept the chimney then disassembled the last 2'-0" section & scrubbed it with scotch pad. No pin holes.

Next changed out the stovepipe from the stove flue to the first Metalbestos section & inspected that section, no pin holes.

This is my 30th year of burning a pre_EPA Fisher stove in that chimney.

Plan to install galvanized pipe within the Metalbestos chimney next month.

Figure the galvanize pipe will last ten years before self destructing into the clean out "T" behind the Stove.

That buys me ten years to see if Pug_lucy, owlore, et al succeed in their version of "cap & steal". ;-)

@ 1990 was asked to inspect a masonry chimney in a beautiful home that was less then 10 years old.

The complaint was that it would not draw in cool weather.

It was a large two flue chimney that really complimented the house.

But one flue was completely blocked at the ceiling height with creosote, soot, whatever.

If you plan to dump an EPA stove output into a masonry chimney your buildup will be worse.

So suggestion:

Search masonry chimney on this forum & get your learning the easy way, & for free.

Can't beat free.

Again, good luck with it & welcome to the forum.

 

[MI Feller]

Thanks All. Great Discussion. When punched a hole in the roof 30 years ago and stuck in the insulated metal, I never dreamed it would serve faithfully this long. At first this was a second home, so it didn't get the full time use lke now. In northern Mich stove burns 10 months of the year. Don't like to bank it down, so mostly wide open using size and type wood to control output. Anyway, a reputable experienced building tradesman would construct the chimney along with an addition. He's had experience building masonry chimneys but maybe not the "expert" a full time mason would be. Footing could go in outdoors prior to constructing the addition but would end up on an interior wall fully visible up to the roof. Yes, cased in metal would work and you have me thinkking. But it's hard to duplicate the look and feel of real masonry. Also desire a clean out door just above floor which masonry would easily allow. Potential cracking of tile flue due to accidental over-firing is a real concern and reason to go SS liner. To be honest, with a chim fire I'd rather be standing next to a block chimney. Imagine that's been discussed here before. Don't know why, just a feeling of added safety in the thickness of the concrete. BTW: the metal stays so warm going through the attic that cleaning it twice per year more than enough (Doesn't do much for those roof boards however) Question: Could someone explain the type of insulation that should be used in a masonry chimney. Is it loose fill and how tightly packed? Also wondering how much heat they throw out. Would you expect chimney exterior to feel hot to the touch after a while? Finally, wonder how the cleanout would work on a metal up the side. Would guess there'd be a removable plug at the bottom a few feet off the floor??? Final thought: years ago a neighbor pulled out an old metal thu attic that had served him well and built his own masonry up the side outdoors. Within a year or two he had a bad chimney fire and came close to losing the house. Food for thought. Good Evening.