Galvanized Exterior vs Stainless Exterior Chimney Wall

[builderbob]

Chimneys. Looking at a model of solidpack chimney which comes in two flavors.

One has stainless walls both interior and exterior. Said to be for harsh climates. The other flavor has stainless interior wall and galvanized exterior wall.

If the chimney is going to be installed enclosed within heated envelope of house, except for last 5, 6 feet or so above roofline and even then only maybe 2 feet above a rooftop chase, and in a moderate climate area (3 dozen days/nights below freezing a year), any special reason to need the stainless exterior?

BTB
(the old builderbob)

 

[Gooserider]

Chimneys. Looking at a model of solidpack chimney which comes in two flavors.

One has stainless walls both interior and exterior. Said to be for harsh climates. The other flavor has stainless interior wall and galvanized exterior wall.

If the chimney is going to be installed enclosed within heated envelope of house, except for last 5, 6 feet or so above roofline and even then only maybe 2 feet above a rooftop chase, and in a moderate climate area (3 dozen days/nights below freezing a year), any special reason to need the stainless exterior?

BTB
(the old builderbob)

Mixed answer... You don't need the stainless exterior on the parts of the chimney that are inside the house, regardless of the weather. IMHO you should use the stainless exterior on any parts that are weather exposed REGARDLESS of the climate. The galvanized WILL rust sooner or later if exposed... The other option is that if you build a "chase" to fully enclose the pipe, which many people like to do for cosmetic reasons plus possibly improved draft, then you can go galvie all the way.

Good news - it is possible to mix and match the flavors in most brands as long as you stay with the same product line, thus you can purchase the galvie for most of the distance, and only get the more expensive stainless for the bit that is actually exposed. This lets you get the best advantage of each type for the needed application.

Gooserider

 

[builderbob]

Thanks Goose.

 

[elkimmeg]

Goose gave good advice stainless steel will out live Galvanized. where exposed. But from a code stand point the exposed sections have to be weather resistant and galvanized treatment qualifies as weather treatment. So code wise you could use all galvanived exterior facing. Practicality be prepared for it to rust out sooner tha Stainless much sooner

 

[builderbob]

Goose give good advice stainless steel will out live Galvanized. where exposed. But from a code stand point the exposed sections have to be weather resistant and galvanized treatment qualifies as weather treatment So code wise you could use all galvanived exterior facing. Practicality be prepared for it to rust out sooner tha Stainless much sooner

Thanks. So if a chase enclosed the chimney where it protrudes through the roof, then only the chimney cap would be totally exposed.

Unless code also requires some length of actual chimney pipe (a foot, 8 inches, or whatever) above the top of the chase?

BTB

 

[jtp10181]

All our pipe is galvanized on the outer.... we have ripped out a lot of 20-30+ year old units with galvanized pipe and it rarely has any rust on it.

 

[elkimmeg]

Code wise one has to be 2' taller than the roof or any other part of the structure with in 10' One also has to extend 3' above any part of the roof known as the 10/3 /2 height code
the height is at the point of exit not the top of the cap

 

[builderbob]

All our pipe is galvanized on the outer.... we have ripped out a lot of 20-30+ year old units with galvanized pipe and it rarely has any rust on it.

So galvanized outer skin goes at least 20 years with barely any rust in your experience, meaning it could go 30 years perhaps before serious rust?
And was that exposed galvanized, or were those jobs enclosed pipe, or some exposed some enclosed? And that was in Wisconsin with not the driest or warmest weather around. Wisconsin probably be somewhat similar to western Oregon weatherwise--except maybe a tad colder on average.


BTB

 

[builderbob]

Code wise one has to be 2' taller than the roof or any other part of the structure with in 10' One also has to extend 3' above any part of the roof known as the 10/3 /2 height code
the height is at the point of exit not the top of the cap

I am trying to get an idea, if one has a chase that extends above the rooftop, how far above the top edge of the wood chase itself would the pipe have to extend. Assume the wood chase itself is taller than the roof peak by 3 feet. Then top of pipe could stop right even with top of chase?

Or does it have to go 8" or a foot or something higher than the chase top?

BTB

 

[builderbob]

Or the 2' rule applies to the chase itself, even when the chase is 3 ' over top of roof peak. So metal pipe would have to be 2' exposed above top of wood chase?

BTB

 

[elkimmeg]

No the chimney and chase are consired as one meaning if the chase extends above the roof then that height is factored for code clearance

Maybe not code but I would extend the chimney 8" to a foot . Practical reasons not the have black smoke dirting up your chase exterior then the cap

I would definitely have some separation distance Speaking of a chace assuming it is on the exterior of the building if at all possible I would use a tee to make the first 90 bend I then would install an acccess door in that chase at the tee level when it comes time to clean it you will know the reason why plus it also gives you access for inspectiond what is going on in that chomney without going to the roof. One can use a flashlight and angle a mirror to see. I may have to check code but I believe an access is required If exterior I would also insulate that chase If the chase is interior NFPA211 requires it to be one hour fire code protected..Layman terms 5/8" fire code sheetrock

 

[jtp10181]

All our pipe is galvanized on the outer.... we have ripped out a lot of 20-30+ year old units with galvanized pipe and it rarely has any rust on it.

So galvanized outer skin goes at least 20 years with barely any rust in your experience, meaning it could go 30 years perhaps before serious rust?
And was that exposed galvanized, or were those jobs enclosed pipe, or some exposed some enclosed? And that was in Wisconsin with not the driest or warmest weather around. Wisconsin probably be somewhat similar to western Oregon weatherwise--except maybe a tad colder on average.


BTB

I am just talking about the whole chimney. The top section of which would be exposed. And this is OLD pipe we are talking about. The modern galvanization is much better than it was 20-30 years ago. The only thing I have ever seen get bad is the cap, which is from creosote buildup. Under normal conditions the galvanized is going to last a long long time.

 

[stoveguy2esw]

were it me doing the install even with the chase i would run galv. up to the last section ( the one protruding) and use stainless outer for the last , as elk stated it is better to have the cap elevated a bit to prevent staining of the chase, this is NOT a code requirement but is definately better than having just the cap exposed as you will end up staining the chase over time. this allows the exposed part of the pipe to be stainless outer wall which will not only be more resistant to the elements , it will not stain from soot where it cannot be washed off which happens with galvie, but its nice and shiny up there and looks better. dont get me wrong either pipe would be safe and would last, i just think the stainless looks better up there than the galvie.

note: the pro's who have already posted have hit the nail squarely on the head as far as the code requirements go, heed what they say. and ask questions on anything you are not sure of, this group will not steer you wrong.

 

[Gooserider]

Just as a minor plug for the stainless - if you get galvie, and it gets ugly in the exposed section 20 years from now, I wouldn't put bets on being able to get a replacement section. OTOH, the stainless should stay looking nice for the entire service life of the system. IOW, I'd think of it as insurance for increasing the entire useful life of the chimney setup.

Gooserider

 

[hearthtools]

ICC has two types
Galvalume (Galvanized Aluminum) Paintable
Stainless.

At first We used only the stainless but my Local competitor was using Galvalume and was beating our price so now I only quote the Galvalume and ask if they want to pay extra for the SS

hight out of roof:
3 feet minumum
2 feet above ANTHTHING with in 10 feet.
Straight line from the pipe level to the roof where it hits the roof go above that 2 feet
Or above any AC unit ect.

Pipe out of the chase. I think the manufactures say 9" out of a chase to bottom of cap.

I personally dont like a chase because it has more mantainence (Paint, Roof Flashing) and normally more pipe is needed.
We are in a mild climate and most roofs are 4/12 to 6/12 so pipe out the roof works just fine and is less noticeable.
http://www.hearthtools.com/install/iccpipe.jpg

 

[builderbob]

Thanks all. Very good discussion.

So do I see a consensus for galvanized IF it is in the ENCLOSED chase. Or do some vote for stainless EVEN inside the enclosed chase?

So if I did a chase, one that goes above the roofline, and had pipe go exposed only above top of chase, then I could do galvanized pipe all the way from the zc firplace top to just below top of chase.

Then put a stainless pipe section maybe 18" at the top. Then it could stick above chase 9" or 12", and start 6" to 9" below the top of the chase.

In other words, the galvanized INSIDE an enclosed chase--even the part of the chase on top of the roof--ought to wear perhaps as long as stainless?

But EXPOSED pipe, stainless is going to wear better and longer.

And if I did not have the interior chase extend on up on top of the roof, then I would definately want to go stainless pipe from roofline itself on up.

BTB

 

[builderbob]

ICC has two types
Galvalume (Galvanized Aluminum) Paintable
Stainless.

At first We used only the stainless but my Local competitor was using Galvalume and was beating our price so now I only quote the Galvalume and ask if they want to pay extra for the SS

hight out of roof:
3 feet minumum
2 feet above ANTHTHING with in 10 feet.
Straight line from the pipe level to the roof where it hits the roof go above that 2 feet
Or above any AC unit ect.

Pipe out of the chase. I think the manufactures say 9" out of a chase to bottom of cap.

I personally dont like a chase because it has more mantainence (Paint, Roof Flashing) and normally more pipe is needed.
We are in a mild climate and most roofs are 4/12 to 6/12 so pipe out the roof works just fine and is less noticeable.
http://www.hearthtools.com/install/iccpipe.jpg

I'll have to think about the chase extending on up on the rooftop. Your "maintenance" comments do give pause on that issue. If I went exposed chimney right from the roofline, then might I have to do some brace for the chimney? Say 8 feet or 10 feet above roofline?

You say you used to do all stainless. How has your experience been since then on galvanized rusting or not?

BTB

 

[hearthtools]

8 -10 feet?
what is your pitch 12/12

Most Standard pitch roof your pipe is only out 4.5 to 6 feet depending on pitch.

See the link to photo on the bottom of the last post I did
this show a Taller than normal chimney (for us) with roof brace

 

[builderbob]

This will be for a new house to be constructed. Roof pitch will be probably 4/12 or 5/12 most likely. I was guessing at how far above roof plane that would put the chimney---I never stopped yet to figure out the 10/3/2 stuff for our house plan. The chimney will penetrate the roof near the lower edge.

BTB

 

[builderbob]

FYI,

Wondering about just how long galvanized could last before rusting, I went web surfing.

First I checked the major chimney manufacturers. It seems they all offer an option other than stainless steel, and that is "Galvalume" for the outer skin of solidpack chimney.

This is a coated steel different than simply "galvanized". Galvalume is a patented steel coating process which combines 55% aluminum, 1.6 % silicon, and 43% zinc.

At the below link, website of the Canadian steel manufacturer licensed to use "Galvalume", is a brochure describing the advantages of Galvalume over plain jane galvanized.

In short Galvalume, in actual outdoors field exposure tests lasting 36 years in the US and 17 years in Canada, offers at least twice the corrosion resistance of galvanized. The brochure shows samples of galvanized, Galvalume, and Alum coated. Drastic difference between galvanized and Galvalume per that picture. In all except severe marine exposure, they are projecting 35, 40,45 year useful service lifes.

(broken link removed to http://www.dofasco.ca/bins/doc.asp?rdc_id=516)

Take a look see.

All that said, if I can get a section of stainless steel outer of the pipe I end up choosing, I will use it for the top exposed section. I believe in lots of saftey margin. But I will feel a lot better about the chase enclosed sections of chimney made of Galvalume outer skin, and won't worry about condensation in the chase corroding that outer chimney skin.

BTB

 

[builderbob]

Just as a minor plug for the stainless - if you get galvie, and it gets ugly in the exposed section 20 years from now, I wouldn't put bets on being able to get a replacement section. OTOH, the stainless should stay looking nice for the entire service life of the system. IOW, I'd think of it as insurance for increasing the entire useful life of the chimney setup.

Gooserider

This brings up another question in my mind: IF one were to want to/have to replace a section of chimney (say to top section) some years down the road, can one "untwist" the old section, take it off, and put another new section on?

I was wondering, if when you first assemble chimney sections, if the "twist together", one-eight turn or one-quarter turn, locks the sections together more or less permanently. Or can you untwist an old section without damaging the end of the section below, so that a new section can twist on and fit good and tight?

BTB

 

[builderbob]

Another thought on using stainless steel exterior wall for the top section, despite the good things said about Galvalume corrosion resistance while exposed to weather, is the smoke and especially *creosote* deposists at the chimney area right near the top going to be harder on even Galvalume treated steel than just plain old rain and weather?

BTB

 

[hearthtools]

ICC is not a twist lock

My personal opinion is you seem to overthink some things.
Dude its a chimney
If it is Rated at 2100 deg UL listed and has a life time warrantee Get it

 

[Metal]

I would only use SS if I were using it for oil or coal burning, otherwise it is for looks only(if you like to see your reflection in it). As far as safety goes, the flues are all SS, and if the casing is exposed, you will see any corrosion long before the chimney would be deemed "unsafe for use." Drive around your city and look at roofs, all that B-Vent you see sticking out is galvanized, how many do you see corroding?

 

[builderbob]

ICC is not a twist lock

My personal opinion is you seem to overthink some things.
Dude its a chimney
If it is Rated at 2100 deg UL listed and has a life time warrantee Get it

Speaking of overthinking, after I got the well put in on our property, and was shopping for a pump, I think I drove one of the pump service companies nuts with all my questions. But I gained an understanding, made an informed selection, and am happy with what I got "for the long term". I guess when it comes to questions, I'd rather risk asking the useless question ahead of time rather than find out I did not ask the important question until afterwards.

I really appreciate this forum for not only the specific answers, but also for getting perspective on which questions are the important questions and which are not.

Thanks all.

BTB