How long does stainless steel chimney last with coal?

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charlesosborne2002
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Post By: charlesosborne2002 » Sat. Aug. 18, 2018 10:40 pm

I bought a Vigilant II and it will replace a wood stove. The new stove will be replaced by the same contractor that sold me the wood stove 7 years ago. It was installed with Class A chimney, which will be used for the coal stove. I have seen comments here and elsewhere that coal produces acid deposits that eat away stainless steel chimneys. Is there an approximate lifespan for the chimney burning coal? I have a good chimney sweep, knowlegeable husband and wife team, who have swept it ever other year--they said that is about right for my use. But they don't have coal customers around here. I am sure if I give them the manual they can check all the required maintenance and continue to clean the chimney, though I wonder if it it needs it every year with coal. And I wonder how far down the road I can expect to replace the chimney. I expect to burn about 2 tons a year (small house, usually moderate winters in western KY)--I can use gas heat in fall and spring if needed. I guess the same question applies to the ash pan--how long do they last?

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Post By: franco b » Sun. Aug. 19, 2018 9:48 am

Make sure coal is not wet. I had to replace a chimney in 7 years. The first year was wet coal and cleaning in the first spring revealed a muddy rusty slurry.

Burning some wood after cleaning and again before starting in the fall is recommended, as is leaving the bottom cap off to allow air circulation in the summer.

Used this way the chimney has little rust except perhaps for the rain cap on the top. A friends chimney is over 20 years old. A metal chimney rots from the top down because the gasses are too cool at the top and condensation occurs. The hotter the chimney is run the longer it will last. An inside chimney will last longest because it has less heat loss.

Burning dry coal and cleaning once a year I think you can expect at least 10 years or longer. This is with Metelbestos (Selkirk) who has honored their guarantee in my case with free replacement parts. There are better alloys said to last longer.

charlesosborne2002
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Post By: charlesosborne2002 » Sun. Aug. 19, 2018 11:04 am

Thanks--sounds reasonable. That tells me what to do. I have already opened a few bags and poured them into plastic tubs in the garage where the coal is stored to be sure it dries out. I have not noticed the coal is wet, but some were soaking wet on the outside of the bag, so I was suspicious. I can easily dump bags into plastic tubs for a day or two before using them to watch for water in the bags. At the least I can put fresh coal in the coal shuttle after filling the stove, and let it dry near the stove for 12 hours, yes? The garage will be cold, so drying would be slow.

My hook-up will have the bottom cap in the T connector (for rear venting the stove), so that is a good idea too. I guess I should have the chimney sweep after the season rather than before. Is there any odor from the open chimney in summer? Does the stove or ash pan need a desiccant in summer? Some people put rice in the salt shaker in humid climates to keep the salt dry. I am in The South, but not the deep south. The stove is in an air conditioned room all summer.

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Post By: franco b » Sun. Aug. 19, 2018 11:32 am

The Vig ll is cast iron, so rust should not be a concern as steel would be. A coat of William's stove polish every couple of years should preserve the looks. Use a round shoe polish brush to apply and buff.

You can get odor if the chimney back drafts when cold. The bottom cap I referred to is at the tee outside if your chimney is piped that way.

Order coal early and poke some holes in the bags to allow drying over time. Nut coal will dry much faster than pea. i prefer nut to pea in the Vig, but the stove can burn either.

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warminmn
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Post By: warminmn » Sun. Aug. 19, 2018 1:02 pm

I want to emphasize a word Franco said, to burn wood in it "AFTER" cleaning it in the spring. You do not want to clean it after burning wood as you want a little creosote coating in it thru the summer.

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Post By: charlesosborne2002 » Sun. Aug. 19, 2018 6:21 pm

Ah--I never would have thought of creosote as a protective coating--but it works on railroad ties, yes?

The gives us a chance to burn a wood fire on cool spring evenings after winter is done.
warminmn wrote:
Sun. Aug. 19, 2018 1:02 pm
I want to emphasize a word Franco said, to burn wood in it "AFTER" cleaning it in the spring. You do not want to clean it after burning wood as you want a little creosote coating in it thru the summer.

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lsayre
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Post By: lsayre » Sun. Aug. 19, 2018 6:24 pm

For what its worth, 316T stainless has generally been considered to be the stainless that holds up best to the acidity of coal, given that the liner must also be approved for wood burning.

There is an appreciably more acid resistant stainless liner material available, but it is likely to be found marginal as to durability with regard to its exposure to potential coal flue temperatures, and it would be rapidly degraded at higher wood fire flue gas temperatures, and it is a code violation to use it for either purpose. It is only approved for NG and Propane to my knowledge.

The T in 316T indicates that it has been impregnated with titanium. There are very few choices available that are made of 316T.

As to creosote, I believe it has a caustic nature, as does wood ash, whereas coal and coal ash are acidic. Caustic does not degrade stainless steel to anywhere near the extent that acid does.

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VigIIPeaBurner
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Post By: VigIIPeaBurner » Mon. Aug. 20, 2018 12:31 pm

My interior SS chimney is nearing 19 years of use with no signs of rot. For acid to form from coal fly ash, water is needed. The best practice it to keep the inside as dry as possible.

Run it inside the house with the least length exposed to help maintain internal temperature. Dry coal produces very little water vapor and a hot chimney eliminates the chance for condensation. Summer humidity is a factor if the ash layer isn't thick enough to isolate the SS from the damp acid forming humid air/fly ash mix. My stove room is air conditioned in the NJ summer weather and I keep the air flap open to draw some dryer room air up the chimney to help keep the top sections as dry as possible.

I've burned wood in my stove to light an anthracite fire and for conditioning new cast iron parts. Maybe a 1/2 dozen 'fire place mode' fires for viewing. I can't find anything other than anecdotal evidence that wood creosote preserves SS (Coal tar creosote is what"s used to preserve wood and as bituminous concrete driveway sealer). Burning wood produces a lot of water vapor which could react with dry ash to form sulfuric acid and become sealed against the SS surface. It's a hit and miss thing IMHO. The pH of wood creosote is right around neutral (7-8 pH) and will do little to neutralize any sulfuric acid produced by the water vapor from the combusting wood. I'd never do it as a preventive measure nor would I swab the SS chimney with a baking soda/water slurry for the same reasons as above.

Your best steps toward preventing water vapor is to burn dry coal. I've burned quite a few tons of damp to wet bulk coal and haven't seen any issues yet. It's just not a good practice when venting with a SS chimney. Draining the bags of coal a good idea. I refill my two hods right after filling the stove and sit them next to the Vigilant II to dry for the next 12+ hours.

Here's a couple pics of my chimney before & after brushing. Th before pic is after about 5 years and burning ~20 ton (4/winter).
ImageImage

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gardener
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Post By: gardener » Fri. Oct. 19, 2018 10:01 am

Anyone try using a protective coating of vegetable oil on stainless steel liner?

( oiling metal flue liner )
I read this in a DS Machines manual, and asked them about it, they replied "Our install crew applies the oil by running the poly brush to clean it,then you wrap a rag soaked in oil to the brush to coat the inside."

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Post By: Bubbalowe » Fri. Oct. 19, 2018 10:54 am

Does formation of sulphuric acid occur with anthracite? Bituminous has 0.7%-4.0% sulphur and anthracite 0.6%-0.8%, trying to understand how SS will rust out burning coal. I have 20' of 6" double wall stainless inside a masonry chimney which looks as good as the day it was put up 12 years ago. Every fall when I dropped a brush down no more than a couple cups of soot came out when burning wood with an Encore cat stove. Don't want to think I'm going backward on chimney life switching to coal.

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Post By: franco b » Fri. Oct. 19, 2018 11:14 am

Do not burn wet coal for longest life. The hydrogen in coal will also condense as water, so a stack temperature high enough to keep it as a vapor will also help.

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