selkirk vent and corn

johninwi · Aug 24, 2014

I have a pc45 with Selkirk model VP venting, the VP is a PL rated pipe.
Venting is out the stove to a horizontal T (easy access), 12" to a 90, into the existing chimney, 90 up and out from basement, total rise about 24 feet. In the chimney is all Vp pipe not flex, it was actually a bit cheaper.

Question is, at what % of corn does the exhaust become corrosive enough to damage the pipe? I've read most people will run 50% corn without combustion issue's but has there been any observations of the pipe deterioration?

I'd assume Selkirk would say pellets only and any corn or other biofuels would require the DT-M series pipe.

This brings another question to mind, what is the life expectancy of a vent? And when it does fail where is the most likely spot?

yep, my mind wanders

Bioburner · Aug 24, 2014

I have found the failure to be near the end of the venting outside where the exhaust cools and condenses eating holes in the pipes. I have posted some ugly pictures but not near main computer this afternoon. Enjoying the deck after its cleaning this AM and a strawberry daiquiri.

Bioburner · Aug 24, 2014

Outside and connected to the vent hood

Ignition temp of corn is almost 200 degrees higher than wood pellets and is why have to use a air pump or start with wood pellets mix.

Bioburner · Aug 24, 2014

Yes, pin holes in it. They stop as soon as the pipe enters the thimble. The weather is a factor as we sit at well below zero for months and sometimes need to knock off the ice off the hood.

Bioburner · Aug 24, 2014

Condensation theory very much so. But having run a straight pellet stove without it eating the pipes and a corn stove and having grief it is that the corn has far more acid. I should save and compare ph levels next season.I shoved a real piece of single wall stainless inside of the venting of one stove last year and it has no signs of corrosion. None, zip.They just make the venting to cheap to last. But only need to replace end piece every third season. This years price difference is over $120 a ton. If use over 4 tons that's $480 to go to replacing a less than $50 pipe. Now having looked at the Harman that burnt 50% blend seems to have no issue after one season and one season of straight pellets. Will be burning a blend this season as the boiler loop in stove does not like to idle well on straight corn as it wants to cycle on and off as the corn burns hotter so easier to blend and keep the stove from wanting to shut down and keep the infloor nice and toasty. Yes I know this post is a bit long.

johninwi · Aug 24, 2014

Bioburner said:
Yes, pin holes in it. They stop as soon as the pipe enters the thimble.

Bioburner said:
I shoved a real piece of single wall stainless inside of the venting of one stove last year and it has no signs of corrosion.

This is much appreciated, i have a few inches of pipe above the chimney and the top foot or so of chimney is stuffed with fiberglass, I have a cleanout into the chimney and know it's quite warm inside at basement level and guessing the top is warmer still. Looks like i'll be doing a detailed inspection of the top few feet of pipe. Also thinking of adding the sacrificial sleeve while i'm at it. Bio, might i ask what you used as the slide in?
Also, the pic, i'm guessing that was a horizontal direct vent? Were the pin holes evenly distributed or were they at the bottom where the ash lay (still assuming horizontal).

Mt Bob · Aug 25, 2014

chickenman said:
Too long, nah perfect.
So you reckon that the creosote composition has higher ph in the corn? Sounds feasible. And quality pipe that doesn't actually cost much more is well worthwhile.
Mixing fuels can also give an improved burn as you can get the best from both sources. WE run a 2/1 mix of pits and wheat for the extra heat of the wheat and the longer burn time between clean outs of the pits.
It is like "hybrid vigour" in cattle breeding. Equally running different grains together or pits with pellets has the impact of running worse than any of the original fuels as they are to close together.

Just have to disagree,no true creosote from grains,Damage comes from the residual acids left over from the burn process.Bio has been doing it for years,trust himLook up old info on dove stoves(corn stoves)they figured it out in the 80's,dual(preheated) vent,still many of them running.But creosote from grain?don't think so(unless there is a language difference).I may be wrong,if so,sorry.

Mt Bob · Aug 27, 2014

chickenman said:
Hi Bob,
OK I might have used creosote as a generic term for the black muck that comes out of a cool burn from grain. My hypothesis is that if the exhaust stays hot and dry then the corn exhaust is no more corrosive than pellet exhaust. That the residual acid is in the damp build up rather than the clear exhaust.
Yes the old dual vent is best, it surprises me that in is still not in general use.

I will disagree about being dry keeping corrosion down,but the corn burners here would know way more than me.I cannot see battery acid in the air(vapors) but it will kill.Have been doing a lot of research lately,appears preheating the combustion air(pellet stove) over a tall heigth or long length cools the output too much,causing much more buildup.Also tall regular stacks do the same.Probably why more places are reccomending an insulated liner inside a chimney.All this affects the units efficency.The old bixby/snowflame and your system is best,short straight out.Another thing people do not realise is when running an oak it is the same as a direct vent heater,when it is not running the firebox becomes a reverse heat exchanger.Found this out many years ago,which is why my lpg wall unit is a pilot system,even though it does waste some fuel.I think the direct vent system was designed back in the 30's?

rich2500 · Aug 28, 2014

I have been burning 20 - 30% mix for 10 yrs. with the duravent pipe(non multifuel) and it looks like brand new yet,I completely disassembled the vent last year and inspected it when installing the new stove and all is good.

Bioburner · Aug 28, 2014

johninwi said:
This is much appreciated, i have a few inches of pipe above the chimney and the top foot or so of chimney is stuffed with fiberglass, I have a cleanout into the chimney and know it's quite warm inside at basement level and guessing the top is warmer still. Looks like i'll be doing a detailed inspection of the top few feet of pipe. Also thinking of adding the sacrificial sleeve while i'm at it. Bio, might i ask what you used as the slide in?
Also, the pic, i'm guessing that was a horizontal direct vent? Were the pin holes evenly distributed or were they at the bottom where the ash lay (still assuming horizontal).

The holes are primarily where the ash and condensate lay. I can't remember what the stainless was that I used as a sleeve. Got from Guy metals as a swap. Told them what I was trying to do.

Mt Bob · Aug 28, 2014

The way corn prices have tanked wish there was some local,I would get some.Going to make some more calls.

johninwi · Aug 28, 2014

Bioburner said:
The holes are primarily where the ash and condensate lay. I can't remember what the stainless was that I used as a sleeve. Got from Guy metals as a swap. Told them what I was trying to do.

If the corrosion is limited to the outside section of pipe and where the ash lay that help a great deal, mine is vertical and about 10" exposed out of the chimney, i may not worry or i'll add a few feet of single wall and let it take the corrosion, toss it when it's done and add another.

rich2500 said:
I have been burning 20 - 30% mix for 10 yrs. with the duravent pipe(non multifuel) and it looks like brand new yet,I completely disassembled the vent last year and inspected it when installing the new stove and all is good.

that was good to read, i get started thinking about the "what if's" and it tends to get expensive.

chickenman said:
The exit temp is the best gauge for flues; horizontal or vertical we have many 20' high balanced flues

elaborate please, both the temp gauge and a balanced flue, I had assumed the exhaust temp was controlled by the ESP. Or is the extra length of vertical adding to the draft of the vent and the temp?
I would assume it would.
I had thought that doing anything to the flue was forbidden, it's for exhaust only. Or is this just the US. Or i could be totally wrong. Remembering a conversation with a fireplace builder and i was asking about the wood stove pipes that had the cross holes and a fan to blow air thru . His experience was they were responsible for more house fires than any other single device and insurance companies wouldn't allow them. He had a number of reasons and examples, what i took from it was to not touch the flue, period.

As a kid i would ask mom why, and rather than tell me she's say, "go look it up", it was no longer a request at this point, reporting back was implied. I guess i learned the lesson well. off searching i go.
Thanks guys, appreciate the info

johninwi · Aug 29, 2014

chickenman said:
No mystery behind the balanced flue. You just bring the intake air down the outside of the hot pipe.

chickenman said:
Extra length definitely adds to draft. Extra draft means higher flue temp. It is a balancing act to get it right.

Makes better sense, was first envisioning a barometric damper or something added to the vent and since these are really a pressurized system that would be a very bad idea.
A magnehelic gauge or manometer would aid greatly in this, for those of us that don't setup stove on a daily basis that is.

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