Rusty Stove Pipe Mysterie

[mxyplx]

We replaced our airtight sheet metal no-longer-legal-but superior stove with a "modern" contrivance (stove) because age took its toll ie it burned out. With the new "modern" contrivance (stove) we then got a big rust streak down each side of the roof below the stack. Oxalic acid removed the stain but we never had that happen for the 25 years we used the airtight no-longer-legal-but superior stove.

What was rusting? Detailed investigation revealed that the inside top 1/2 portion of the single walled stack between the stove and ceiling is rusty; about 2.5 feet. The triple walled pipe thru the ceiling/attic is not rusty.

Certainly one of the products of combustion is water. Of course the wood is not perfectly dry - it is dryed in 100º heat most of the summer - but absorbs some moisture from the air even tho its stored in a shed. So that's the source of the water. The said water must condense on the inside of the pipe to cause it to rust. For that to happen the temp of the pipe must be below the dewpoint of the water in the hot xost gases rising from the stove. How can that be?

I often at bedtime throw in a relatively large bunk log, get it burning then damper the stove down for overnight. In the morning the house is warm but the pipe is or may be touchable - you can lay a hand on it. The stove likewise. The log is sometimes gone and sometimes there is still some of it left.

I believe it is during this cooler operation that the condensation and rust formation occurs. I believe it did not occur with the airtight no-longer-legal-but-superior stove because it had an automatic damper which would be wide open in the morning. That is, it would open as the stove cooled, increasing air flow and preventing the relatively incomplete combustion and lower xost gas temperature which must occur in the "modern" contrivance (stove) with its non-automatic damper.

There must be a temperature gradient up the pipe. The single wall pipe radiates to the room and cools. The top 1/2 is coolest. The triple wall pipe inner surface thru the roof probly stays hotter the whole time since it is shielded by its 2 outer walls.

So it would seem that the most practicable solution to prevent rust is the use a double wall pipe from the stove to the ceiling thus shielding the inner wall and allowing it to stay (hopefully) hot enough that condesation does not occur. A caveat is that we'd not get the heat previously radiated from the 1-walled pipe.

Is my analysis valid? Is there another solution? Should I heat the upper half of the pipe ? Waddaythink?

 

[Backwoods Savage]

Some of your comments rather confuses me. For instance, you keep mentioning your, "no-longer-legal-but-superior stove." Just exactly why do you feel your former stove was superior? It seems that you feel there is something wrong with your present stove. What is this present stove that you have?

btw, we also replaced our airtight stove with a, "modern contrivance (stove)" and couldn't be happier! The top three things we like about our present stove is:
1. We burn a lot less wood. A lot less.
2. We stay much warmer. A lot warmer with less wood burned.
3. It is a beautiful stove.

Another of your comments also confuses me. Your wood is absorbing moisture from inside a woodshed?! That is a new one on me. If that wood is dry when it is put inside the woodshed I don't see how it would draw enough moisture to cause any problems in the least.

Also, if that wood has drawn moisture, you would have creosote inside the chimney rather than rust.

When you put wood on the fire, the first thing that happens is the remaining moisture is evaporated and that is why you get so much smoke at the start of a new fire. That also is hot while going up the chimney and would not cause rust.

It seems to me you have some other problem and I'll allow the more professional stove people answer that.

Hope this all works out for you. Good luck.

 

[begreen]

Could be right. Double wall pipe will help, it's stainless lined. The best solution is a combination of the double-wall pipe and dry wood.

 

[mxyplx]

Never woulda thunk it.

The new stove originally had double wall pipe. Telescoping. I just now went out and lookt it over - sure enough the upper portion is stainless (non-magnetic anyway). One might presume then that this problem has been addressed before. I had replaced it with the single wall. Must not have used it much - only thin amount of soot in it. I'll reinstall it for this winter; see how it goes. Hope the bottom part don't rust - we'll see.
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1. The airtight was a sheet metal stove and setup strong convection currents which heated the whole house. The new is a cast iron stove which is primarily radiant heat and very very secondarily convective heat and does not really heat the whole house. For that reason a blower is not too effective - helps yes - but not substantially.

In fact the double walled sheet metal stove actually shielded the firebox so radiation was extremely minor which, of course, enhanced the natural convection.

2. Wood for the new outfit has to be cut just so - the old one you could throw in odd size and odd shaped stuff - open the door and toss. Not this dude.

Its a Regency 1100 which is the only one that would legally fit our geometry w/o drastic remodeling. I bot it for that reason only. Sun don't rise and set on it. For Sure!

I stated the sources of water so I wouldn't get a lecture on using dry wood and/or basic combustion processes. Actually wood is hygroscopic ie it absorbs water from the atmosphere. Since the humidity is higher during the rainy season presumably the stacked wood absorbs some even in the shed.

Certainly creosote forms in the chimney and has to be and is clun out periodically. But the creosoe is black and light and what doesn't cling to the pipe floats away in the smoke; the rust must exit the pipe as rusty water vapor which is heavy and condenses onto the roof.

Maybe I shoud heat the roof?
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Perhaps if the stove was run totally hot at all times neither creosote nor rust would occur but it completely escapes me how a stove can be ran totally hot at all times and still live in the house same time.
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Thankyou gentlemen - that should be the end of all my problems. Well maybe not all....

 

[begreen]

I believe the Regency 1100 is a small steel stove, not cast iron. Is this the new stove or the old stove?

 

[fossil]

I think this Regency is a steel stove with a cast iron framed door. Rick

 

[RedRanger]

Mxyplx: where on the left,west coast are you? I am curious because I used to put my wood directly into the sheds when it got delivered and it didn`t dry worth sh8*&!! Matter of fact it seemed to attract mold and mildew. We get a fair amount of rain here on Vancouver Island, but even still my wood dries very nicely when stacked in rows outside from March till Sept. Then I bring it into the sheds if there is room or else just cover with tarps. Wind and sun is our friend for wood drying.

As for the new insert with your 1.4 cu.ft firebox. yes its small but it should burn hot and clean. Just got my new one in april this year and noticed that it is not as tolerant with semi-seasoned wood as my older PE. Indeed, these new puppies seem to demand perfectly seasoned wood, that is to say that any wood over 25% moisture content will be a problem. 20% is ideal. Maybe invest a couple of bucks in a moisture meter? Then later this fall, split a couple of pieces and take the reading from the inside of the split. You might find your wood isn`t as dry as you thought? That little gadget sure opened my eyes!!

Good luck and happy burning.

 

[Redox]

You left coasters and moisture! C'mon over here, I'll show you moisture! ;-)

It would seem to me that your climate may not be extreme enough to allow a full hot burn. Triple wall stack and single wall connector will make this problem worse. Insulation is your friend in this case and the double wall connector inside will help. Those EPA approved contrivances put less heat up the stack and will show up cold spots. You might even consider replacing the triple wall with an insulated double wall system that will help out even more.

After you get some more burn time under your belt you will come to appreciate the contrivance. Less wood and more heat is a good thing. The differences between the old and new amount to idiosyncracies that you will soon learn and develop workarounds for. Relax and work with it a bit; you might be surprised what it will do over the long run.

Chris

 

[mxyplx]

Yah its steel - execute me please. Used it 4 seasons now.

BC:
I live in N. Calif. The split wood gets stacked log cabin style or what we used to call council fire style from May thru Late August and the temp gets over 100ºF many days in a row during July and August. Except this year the smoke is keeping the temp down in the low 90's so far. Anyway the wind blows thru ---its dry. The lumber mills hereabouts air dry lumber this way but they're mostly gone now.

Yes it burns nice and hot and clean till it gets too hot then what are you sposed to do? Put it out? When you start to shiver start it up? Waste all your kindling? Matches? Newspaper? Naw, I just damper it down, let it smolder, throw some wood in now and then. Long as it don't rust is all I care.

Mostly we need the fire from maybe 3am till 10am. If I fire it up at 10pm and let it soak all night the front of the house is warm when we get up at 5am. (Bedrooms are open and cold [60º eat your heart out] less it rains). We feed it till about 10am but it has to be dampered down or it drives us out of the living room.

Conversley if we fire it up at 3 am the place never really gets fully warmed up till 8am then its too late.

OX:
You are correct, the climate is not extreme enough for a full hot burn, by which you must mean a long hot burn. I am looking forward to using my SS lined double wall pipe and no rust on the roof.

 

[Redox]

Yup, sounds like a P R O T R A C T E D learning curve due to environmental factors. Let's call it "terminal shoulder season", if you will.

Kinda like a motorcycle, it's easy to ride fast and hard and harder to ride slow and graceful. You should not have to be making large changes in the air control to maintain a burn. I'm not familiar with your particular stove, but I've found that mine burns best around 1/2 open. Damper back to 1/4 or so in mild weather and keep more than 1 piece of wood in the firebox at a time. I've found that it really helps to have 2-3 smaller pieces next to each other as the heat reflects off its neighbor and helps keep a clean burn. Anything between 1/4 and closed is chancy as to how well it will do. Full closed will generally still allow some air, but will really slow things down if your are running hot.

Ceiling fans and other forms of air movement are also helpful in spreading the heat through the house.

Chris

 

[mxyplx]

Hello Again-

I removed the single wall pipe. I could find absolutely zero rust inside that pipe. None in the triple wall pipe thru the attic, none in the exposed stack above the roof and none in the stove except:

1) red droplet spalsh marks and
2) red color or stain on the baffle blocks.

It would appear like rusty water precipitated out.

Beats me where the rust came from.

I put the single wall pipe back in cause it fits and there seems to be an adapter missing for the doudble wall pipe.

Guess there will be one more weekly chore this winter - spraying oxalic acid on the roof and washing it off. What a drag.