Effect of Coal Exhaust Gas on Pipe

Hello,
I am installing a Keystoker boiler in a insulated shed and plan to exhaust it via metal pipe up through the roof. While pricing insulated double wall stainless pipe today, the man behind the counter said I'd be lucky to get a few years use out the stainless and even less from galvanized due to the highly corrosive property of coal gas.
Is this how it really is? And if it is, can it be slowed down.
Also my boiler has an 8" outlet flange. Is it OK to reduce to 7" at the double wall? The manual says reduce at the thimble and I assume a reduction at the double wall as it goes through the ceiling and roof would be acceptable.

Thank you for your thoughts

Chris

This is a question that comes up a lot. Some hate stainless some like it. I have 20 year old metalbestos that is in ok shape on the inside of the pipe but has a couple pin holes on the outside of the top section of pipe.

I am in the minority with respect to SS insulated pipe performance. Others always report quick degrading of the SS. However, I used a hand fed from Jan 1993 to 2011 and a stoker last winter in this house using the same exterior SS insulated chimney. The chimney is still in good shape, the only part that corroded away was the screen on the chimney cap (lasted about 10 years) and the bracket on that cap (lasted until two years ago). I never replaced the screen and I MacGiever'ed some 12awg copper to hold the cap on last fall. The copper held up fine through last winter's use.

I was satisfied enough to install a SS double wall chimney for the stoker in the workshop two winters ago.

I clean it out each spring and fall with a metal brush.

I also have a the same SS thimble from the Jan '93 install and it is fine.

There's a small chance you'll get longer than two seasons out of it, but, why not just throw up a masonry stack for about the same price (materials/labor) and not have to worry? The 8" stainless pipe is pricey -and it's usually the same or less to pay someone to throw up a stack using chimney block. The few that have gotten good life from their stainless stacks are not the norm.

I've seen them fail firsthand - I've even seen 316 fail with heating oil. Coal attacks stainless especailly well through three mechanisms - pitting corrosion from deposition of iron particulate, Chlorine/HCL, and Sulfuric acid. The lack of oxygen in coal gas prevents replenishment of the passivation layer and any moisture rapidly accellerates this process. It's not so much a matter of "like" or "hate" but, rather, what has a significant chance of holding up what doesn't.

For every rule there is an exception, but, it's more likely that an individual install will have conditions that foster corrosion than having perfect conditions that do not. The man who recommended against the stainless you were trying to purchase from him is a VERY honest businessman and I would say that he was doing you a service by being so honest.

Block chimney was cheaper for me then SS one. Benefit for block its one time project, SS will need to be replace sooner then later. Where do live, maybe someone can refer a masonry

IMHO everything you hear, pro and con, is right on the mark. There's one thing that didn't get mentioned. Moisture. Acid can't work without a small amount of water. If it's in a year round dry location where there's minimal humidity, it should last. There are sulfur compounds in coal gas and fly ash that need moisture to become corrosive. If it's dry, nothing should happen quickly, just like the testimonies above. If it can get damp for an extended period or get below the dew point temperature when shut down, stay with a masonry chimney and choose your poison on which stove pipe you go with. My system (ss chimney & double walled SS pipe) stays warm and dry and is in good shape after 12 (+?) years.

i was at the same point untill I had someone point me in the direction of an amish fellow that makes stainless chimneys for a living. 10 ft of stainless single wall for in the garage, triple wall thimble, 12 ft of double wall outside. nice weathervane cap, all brackets, 90s, t's and straps, just under 500 $. but there is no arguement that a masonry chimney will last a lifetime. like the rest of the guys say, once and done. the shed being dry will help with the inside pipe from rusting. it seems like that most people that have problems have a wet basement, in a shed, or shop you shouldnt have that problem. good luck with your install. I put my keystoker boiler in my shop and absolutely love it!

sinistrafatboy wrote:Hello,
I am installing a Keystoker boiler in a insulated shed and plan to exhaust it via metal pipe up through the roof. While pricing insulated double wall stainless pipe today, the man behind the counter said I'd be lucky to get a few years use out the stainless and even less from galvanized due to the highly corrosive property of coal gas.
Is this how it really is? And if it is, can it be slowed down.
Also my boiler has an 8" outlet flange. Is it OK to reduce to 7" at the double wall? The manual says reduce at the thimble and I assume a reduction at the double wall as it goes through the ceiling and roof would be acceptable.

Thank you for your thoughts

Chris

Keep it 8" all of the way out, especially with a short chimney.

There are various grades of stainless. The 400 series is a cheap stainless that some chimneys are made of. Stay away from this for the inner liner. Ok for the outer liner.
316L is the best choice for an inner liner for coal.
Olympia has the best warranty for coal.
http://www.olympiachimney.com/products/cat/VCAA/

I used amish chimney made from 304 ss. I didn't know about Olympia at the time. My chimney on the keystoker looks ok after 1 year. Keeping it dry on the inside and brushing the ash out after the season is a must.

the olympia products look nice, and they are made in Scranton, PA. would love to buy from them but their site says they sell to installers only. Has anyone bought their products, and if so, where?

Has anyone bought their products, and if so, where?

PM Windago

Olympia Chimney Dealer

I had a 316L Stainless steel liner put in this fall buy Mauch Chunk Chimney Sweeps out of Jim Thorpe, they use Olympia Products.

I have customers with 25 year old Metalbestos 316 inner liner chimneys and 316 liners that are fine after all these years of coal use. On the other hand, non 316 product will probably fail. On the other Other Hand, I see people with what I consider lower quality chimney (400 series) who have been using it with coal for years without a problem.
So, I guess I would say.............I don't know.