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Pellet pipe 3 vs 4 inch

Post in 'The Pellet Mill - Pellet and Multifuel Stoves' started by irenearcher, Jan 28, 2008.

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  1. irenearcher

    irenearcher New Member

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    We are having a Harmon installed where we used to have a wood stove. The venting pipe will be 12 ft from start to finish but there will also be two 45's. I understand that means my length will really be 15 feet since factoring in the 45's increases the length. So we are just at the maximum length for using 3 inch ICC Pipe. Since we are at that limit should we consider using 4 inch just to be sure we have less flow resistance? You know just to be extra vigilant? Will the stove be more efficient in general if we do this?? Also is it really ok to adapt to the old woodstove box and chimney rather than run new pellet pipe all the way through the ceiling including the chimney? Will that adaption from 3 to 6 or 3 to 8 (not sure which it is yet) be ok with the fire regulations?

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  2. jtp10181

    jtp10181 Minister of Fire

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    Most manuals show adapting from the pellet vent to 6" wood stove chimney. Personally I would either transition to a liner at that point or run rigid all the way up. Ash will collect at thew transition point otherwise...

    I dunno... just read the manual.
  3. irenearcher

    irenearcher New Member

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    I did study the manual carefully and it does not really address the topic of the transition to a 6 inch wood stove chimney. They just go through the different options for ventilation of the Harmon Pellet stove. The option they show for through the roof ventilation seems to assume you will do it for the first time using just the 3 inch all the way. I can only rely on the man who is doing the installation. He is a Harmon dealer. But he is not very fussy at all. His own stove at home is a simple direct vent with no outside air. Therefore i feel i need to be pro active here. Would appreciate some help if anyone knows. My question was two fold. Should i go up to 4 inch pipe instead of 3 since the pipe run is just at 15 ft or would that be over kill? Other question was about the 3 inch pellet pipe to the wood stove box and if it is ok to connect to that with an adapter from ICC and use the old box and chimney. You suggested a liner but I am not sure what a liner is? And when you say run rigid all the way you mean use the 3 or 4 inch pellet pipe all the way right? What is the thew transition point? Thanks from a lady at the mercy of Iowa country bumkins.
  4. jtp10181

    jtp10181 Minister of Fire

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    What Harman model are you getting?

    Is the chimney 15' total, or is it 15' just to the old wood chimney?
  5. Justaddwater

    Justaddwater New Member

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    Hello Irene, I just installed (two weeks ago) a Harman xxv with the top vent adapter. It replaces my wood stove and outlets into the same chimney. I ran 6 inch black seemless to a 6 to 8 adapter. My prefab chimney for my wood stove is 8 inch. the 4 inch PL vent pipe only extends 12 inches above the stove (per manual) and then it is sealed 6 to the 8 prefab. Works like a charm. The added draw you get from the wood stove chimney will elimate/reduce any smoke issues during a power outage.

    You don't need a liner once your 4 inch ties into your chimney. Just make sure you seal all joints with high temp silicon (per owners manual) upto the chimney thimble.

    Good luck- which Harman did you purchase.
  6. irenearcher

    irenearcher New Member

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    Pyro: my new pellet pipe will end up being around 12 ft give or take but with 2, 45's i am told i should just consider that 15 feet. I am counting from the point where the pipe starts at the back of the stove to the very top of the chimney for the 12 feet estimate. The stove i am getting is the Accentra.

    Firestarter: So if i understand you are saying you have 4 inch coming out of your xxv stove for 12 inches and then that goes to 6 inches and up at the box or chimney at the ceiling it adapts to an 8 inch chimney pipe? Do i have that right???

    So with my new Accentra, I was considering asking him to use 4 inch pipe rather than 3 from the back of the stove all the way up to the box at the top of the ceiling. That box is probably for an 8 inch chimney pipe right now. I think the current sleeve coming out of the box is 6 and my woodstove pipe is 6 inch. but the chimney looks bigger. So for this new stove i basically need the 4 inch ICC pipe all the way up to the box and then an ICC adapter that goes from 4 inch pipe to 6 (the guy at ICC seemed to think i should measure the sleeve)?

    When you say to seal the joints up to the chimney thimble where is that? Just seal any joints all the way up to the very top of the chimney? Can you use that silicone tape or is the silcone better?

    Also what if my old chimney is not in good shape? Not sure of that till i have it looked at. But if it is not so great i assume i should just start with all new ICC pellet stuff all the way up?

    Or, if i have the choice to relocate the new pellet stove to another spot that would have a straight vertical, shorter pipe run and brand new chimney, would that be significantly better and justify the extra cost of a new hole in the roof?

    I sure am being a pest. Thank you.
  7. flueinc

    flueinc New Member

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    #1With icc pipe you do not need to use silicone it is self sealing. All you need is the three inch pipe with the adaptor to your chimney. your stove shop or chimney sweep should check your chimney before you install anything .
  8. irenearcher

    irenearcher New Member

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    Firestarter: OK great that the ICC is self sealing. What about the two 45's? Will those be self sealing too? I have lung issues hence my decision to go to a pellet from a wood stove. So you think i should just use the 3 inch pipe up to the box and not the 4 inch? I have the equivalent of 15ft which is the point at which they suggest up grading to 4 inch rather than 3 but i am not over 15 ft. By the way i just looked up the xxv and i see about the top vent adapter that comes with that stove. Sorry i did not understand that until l looked that up. Thanks again very much.
  9. MainePellethead

    MainePellethead Minister of Fire

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    I love the ICC pipe...looks nice, works very well. I went up 8' but plan on going above the roof later in the year.
  10. Justaddwater

    Justaddwater New Member

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    Irene, My xxv has a special adapter from factory to convert 4inch from back of stove to six inch black pipe. I'm not sure how the accentra exhaust. My point was that venting into an existing chimney will work. As long as the chimney is in working order. Justaddwater.
  11. pegdot

    pegdot New Member

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    Hey Irene! I can understand your discomfort with this installer. It doesn't sound like he much cares about safety or efficiency. There are several ways you can go with this installation. The first thing is to have your existing pipe checked out. If it's in good shape you can certainly attach to it but the problem with changing pipe size is that soot will catch in the adapter and make cleaning the vent pipe harder. If your existing pipe is in poor shape or you just really want to err on the side of caution you could have a flexible or rigid liner installed down through the old wood stove pipe. That would eliminate the cleaning issue and ensure the best exhaust without making any radical changes to your roof.

    I think if it were me I'd go with the four inch just to be sure. The pipe is pretty pricey and it would be a shame to install 3" and then have to replace it if it didn't exhaust well.

    One thing I'm confused about. Is your existing pipe inside a brick chimney? Is it inside the house or on an exterior wall?

    You might want to look through your local yellow pages and see if you can find a chimney sweep to do the pipe installation and just let the dealer deliver and set up the stove.
  12. galen

    galen New Member

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    Irene, I'm on the side of 4". It will draft better. As for the exiting pipe, since you are unsure of its condition, and feel uneasy about it, I would pay for a third party unbiased opinion. Then make your decision. But I believe all would think 4" is better than 3".
  13. irenearcher

    irenearcher New Member

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    Thanks Peggy. Sounds like i should go with the 4 inch then. It would be a shame to have to buy it twice! I know this guy will tell me i dont need to since i think he already has the 3 inch in stock. My existing pipe is for a wood stove so the whole thing is in the house. With wood stoves the pipe usually goes up through a black box at the ceiling as does mine. Yes i will have my local wood stove guy give me an opinion when he takes out the old wood stove. He is reliable and careful.

    I guess with all this expense of the long 4 inch and the two elbows (this helps to get the pellet stove closer to the wall) i should probably consider putting the pellet stove in the corner instead. This would require a new hole in the roof and patching up the old hole. But the pipe would be 3 inch and shorter and straight since our ceilings slope down. I also would not have to look at so much pipe in the house. I just wonder how big a deal it is to put in a new chimney through the roof.
  14. pete324rocket

    pete324rocket Feeling the Heat

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    Hmmm,should I give my 2 cents worth? I was going to use 4 inch icc pipe but the place I was buying the pipe said no-not necessary and a waste of money.I am venting into a chimney with a 6" stainless liner-I have 2 - 90 degrees and maybe 8 feet of pipe in total before it hits the pipe adapter to the stainless chimney liner. My point is that the chimney provides a huge draw to the stove-I knew this when I had the old wood stove hooked in-only problem I ever had was a normal one when it was really cold out and had to get the heat flowing first or the stove would smoke on start-up. The pellet stove beats this with the exhaust fan.
  15. irenearcher

    irenearcher New Member

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    Well i am not an expert but are you talking about a fire place chimney or just the wood stove's chimney? In our case it is the wood stove chimney that would be used and the pipe length for the pellet stove would equal 15 ft from the very bottom to the very top including the chimney. The manufacturer recommends that anything over 15 ft you upgrade to 4 ft pipe rather than the usual 3 ft. So since we are at 15 ft i thought to use 4 to be safe. I guess you are saying that since the wood stove chimney is larger (6 or 8 inches) that the draw from that will compensate for the longer pipe length and that i could use 3? Am i making any sense? Is that what you mean? We do get a back draft with our current wood stove on occasion...
  16. sparkydog00

    sparkydog00 Feeling the Heat

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    I believe the Harmen come stock with a 4" outflow (vent). That would simplify the question about 3 or 4 inch pellet pipe.
  17. pete324rocket

    pete324rocket Feeling the Heat

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    Wood stove...just trying to bridge the gap between technical specifications and common sense.
  18. irenearcher

    irenearcher New Member

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    The Harmon has a 3" outlet for the vent.
  19. pegdot

    pegdot New Member

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    ROFL! Now I'm confused! My understanding, and someone PLEASE correct me if I've got it wrong, is that the reason a pellet stove uses a combustion blower, double walled pipe, and a smaller diameter pipe for exhaust is because the exhaust gas is much cooler than that of a wood stove and the cooler exhaust has less natural rise/draw. The smaller double walled pipe serves to insulate the exhaust gas so that it doesn't cool too much before it exits the pipe. Have I got that right?

    If I do, then it just makes sense to me that attaching pellet vent to a larger single wall pipe or chimney would allow the gas to spread out and cool pretty rapidly which would inhibit the draw, not help it. Am I totally off base here?

    Sorry Irene, I know this doesn't directly answer your questions but maybe an understanding of how the exhaust system is designed to work will give you a better idea of what to do.
  20. galen

    galen New Member

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    Peggy, the big difference from wood stoves and pellet stove is wood stoves have a natural convection drawing flue, where a pellet stove has a blower that actually pressurizes the exhaust. The small fire pot blower doesn't have much force but with a concentrated burn area, it will allow direct venting,short distances. If the exhaust run is over so many feet, then a vertical run with an up sizing to 4" maybe required, to minimize back flow during high winds causing poor combustion. A wood stove's exhaust is much hotter and inefficient requiring larger flue sizes. There are other reasons, but this is a short answer.
  21. irenearcher

    irenearcher New Member

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    [quote author="pegdot" date="1201801080"]ROFL! Now I'm confused! My understanding, and someone PLEASE correct me if I've got it wrong, is that the reason a pellet stove uses a combustion blower, double walled pipe, and a smaller diameter pipe for exhaust is because the exhaust gas is much cooler than that of a wood stove and the cooler exhaust has less natural rise/draw. The smaller double walled pipe serves to insulate the exhaust gas so that it doesn't cool too much before it exits the pipe. Have I got that right?

    If I do, then it just makes sense to me that attaching pellet vent to a larger single wall pipe or chimney would allow the gas to spread out and cool pretty rapidly which would inhibit the draw, not help it. Am I totally off base here?


    I am pretty sure they recommend going up to 4 " pipe if your pipe length is over 15 ft. So there must be a reason. I should try calling Harmon to see if i can get an answer. They are not very willing to answer any questions. Maybe the reason for the 4ft is in the event of a power failure? Not sure. I am switching to another dealer so maybe i will be able to find out and get better information. Will post what i find out.
  22. sparkydog00

    sparkydog00 Feeling the Heat

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    Hmm Guess I got the 4 inch option on my Accentra.
    Wait go to the web site.
    The 3 inch is an option.
  23. irenearcher

    irenearcher New Member

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    I looked through the website and i dont see anything about the option of a 4 inch outlet. It just says 3. I assumed there was some sort of adapter. You ordered the actual stove with a 4 inch outlet?
  24. galen

    galen New Member

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    Irene, look at the fireplace insert. On the specs. page there is an option for 3" but 4" is standard.
  25. irenearcher

    irenearcher New Member

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    I looked through the website and i dont see anything about the option of a 4 inch outlet. It just says 3. I assumed there was some sort of adapter. You ordered the actual stove with a 4 inch outlet?[/quote]Irene, look at the fireplace insert. On the specs. page there is an option for 3" but 4" is standard.[/quote]

    I am not getting a fireplace insert. I am getting a free standing Accentra Pellet stove which comes with a 3 inch outlet for the vent pipe. So not sure how i would use 4 inch on that now. It is all rather confusing. Too bad Harmon has such lousy customer service.
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