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Single vs double wall, could use some input

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by rudysmallfry, Jul 29, 2006.

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  1. rudysmallfry

    rudysmallfry Feeling the Heat

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    Hi all,

    I had installed a new hearthstone stove last year. I had a 90 degree elbow in my setup which I believe was contributing to my semi-poor draft. I plan to ammend that to two 45's this year. I figure it can't hurt to try it out.

    The thing I'm grappling with is, should I stay with the single wall pipe, or upgrade to the double wall? There's several pros and cons here which I'm sure some of you have already debated.

    Pros of single wall

    1. Since I have a soapstone stove and do start it from cold on almost a daily basis, I do get my initial heat from the stove pipe while the soapstone is coming up to temp.

    2. I'm also a compulsive stack temp watcher which is very easy to monitor with single wall. I understand is much less accurate with double wall.

    3. It's already there. Double wall is big $$$.

    Pros of double wall

    It's much safer in the event of a creosote flare up. While double wall can handle up to 2100 degrees, I could kiss my house goodbye if my single wall went up. This one alone could be the reason to do it.

    Any advice on which way to go?

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  2. Shane

    Shane Minister of Fire

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    What is the total length of connector? That would be a major factor for me. I wouldn't worry about creosote build up as you are a responsible wood burner who properly operates his appliance and has his appliance serviced at regular intervals, correct? The double wall being SS inner could potentially out last the single wall two to one so that lowers the cost a little. Honestly the only time I really push double wall is when the amount of connector is excessive or for clearance issues.
  3. MountainStoveGuy

    MountainStoveGuy Minister of Fire

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    Your confusing double wall chimney for interior double wall. I dont believe interior double wall can take a 2100 degree chimney fire
    1) you are loosing draft because your single wall is robbing the chimney heat
    2)Its very easy to moniter double wall tems acuratly with a stove thermometer probe.
    3) interior double wall is not as expensive as the class a stuff, but its still more then single wall by a long shot.
    4) stay with the 90 and switch to double wall, i realy dont think that 2 45's will make a huge difference, if your having draft problems its likeley something else, like a lot of exposed exterior chimney on the side of the house, to short of a chimney considering the 90's in the system, to big of a flue for the stove being used, maybe a negative pressure problem that is prevelent untill the stove gets warmed up.
    The first thing i would do is try the double wall black pipe and go from there.
  4. Todd

    Todd Minister of Fire

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    I never used double walled pipe, but seems that most people here are in agreement that double wall and 45 elbows verses 90 degree help draft. How high is your chimney? Can you add on? As far as a thermometer you could use a probe thermometer.
  5. KP Matt

    KP Matt New Member

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    You could go with heavier single wall - say 22 gauge... isn't there even stainless single wall?

    And maybe keep that 90 degree but make it a clean-out T, assuming the 90 degrees is pretty close to the stove. That would make it easier to clean out the stovepipe, if you're worried about creosote. Doesn't help your draft though unfortunately.
  6. rudysmallfry

    rudysmallfry Feeling the Heat

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    The reason I'm attributing the 90 to the draft problem is that, the elbow is the only place that creosote collects. Maybe that's due to the 90 angle itself or some type of temp difference when the air makes the turn up from the stove out toward the wall. Not sure which, but it's the only place I ever see buildup.

    My stove calls for minimum 13' chimney height. Mine is 18'. Subtract a few feet for the 90 where the wall thimble meets the class A chimney, and more for the 90 elbow inside. I don't find any fault with the chimney itself. It's packed insulation. Even with a few bad pieces of green wood last winter, this summer's cleanout showed 0 buildup in the chimney. The sweep said I wasted my money by having him come out. If the draft was due to the chimeny not holding its heat well, I'm thinking there would have been a substantial amount of creosote near the top, yes?

    My draft was measured at .01 on a 25 degree dry day, so I'm thinking it's an accurate measurement.

    The current setup is 3' from stove top exit to 90 degree elbow, another 3' to wall thimble. I was going to try to amend that to three 2' sections with the 45s.

    Sounds like not much reason not to switch to the double wall. The probe thermometer sounds good, and if the double wall alone might help the draft, that's good too.
  7. elkimmeg

    elkimmeg Guest

    Welcome back Rudy ever get that Popular cut up? See I do remember?

    Practicality first of all , you only need one more 90 degree elbow, If you have 24 gage common single wall pipe. Then chances are you have the variable angle elbows that adjust from 90 degrees to straight. You adjust the one in place to 45 degrees and buy another adjustiable one, and you are there. You may even be able to use that verticle piece inbetween or you may need a longer piece. Before you go all out with double wall try this first. Technically 2 45= one 90 but smoke is traveling upward path instead of the abbrupt right angle all at once. Yes 90 elbows are where you will see cresote build up this is common.
  8. rudysmallfry

    rudysmallfry Feeling the Heat

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    Yeah, I'm still working on that poplar pile. I got all of the small stuff split in May. The big pieces are yet to be tackled. Luckily this rippin' hot summer has accelerated the seasoning process. Most of the splits are already cracking on the edges. By the time I get to the rounds, they'll probably just fall apart. I'll get there with my little maul someday.

    Sounds like a good plan. I'll get a second elbow and play with the setup to reduce the sharp angle. The elbow that's there now is pretty solid stuff. I didn't even realize that it was bendable. Silly me.
  9. Todd

    Todd Minister of Fire

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    How long is your total horizontal run including the thimble? That might be the problem. Do your clearances allow you to reduce this run? Also there should be a rise in the horizontal run of pipe from the stove to the thimble. I noticed an increase in my draft when I cut down my horizontal run from 3' to 2' and kept the 90 elbows. Infact I have 3 ea 90's with a 20' outside wall chimney and my draft is great.
  10. hearthtools

    hearthtools Moderator Emeritus

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    Hearthstones are very draft sensitive.
    The build up near the 90 could be from the joint leaking especially if you are using the thin gauge black pipe with an adjustable 90

    Having the double wall pipe will help with draft and faster start ups. The joints are tighter and it will help get the pipe hot sooner and stay a consistent temp. Life time warrantee on most brands of Double wall with 6” clearance to combustibles.

    Your 36”horizontal run to wall thimble might be the problem also. Do you have a rise in the horizontal run? ¾ of on inch rise is what would be need for 3 feet of pipe (1/4” per foot) but then it makes it hard to have a good connection on the Flue in the wall.
    (WHY SO LONG OF A HORIZONTAL RUN?)
    If it is clearance issue then use Hearthstones optional heat shield and double wall pipe and move the stove closer to the wall. What model do you have?
    Use a 24” section with an 18” slip section over it to make up the 36” so you can pull the pipe apart to clean the 90 when needed.

    95% of our installations we use UltraBlack ICC double wall pipe. Or we use Heatfab Heavy gauge welded seam Black single wall pipe.

    Make sure your Screen in you cap is not getting plugged up.
    Do you have high winds, are you on a hill side or a bluff? Wind beater cap might help.

    I don’t like to use Black pipe for up and out the wall installations due to the fact that you do not have 18” clearance on the horizontal pipe that is connected to the Class A at the Thimble/wall radiation shield unless you have a masonry wall.
  11. rudysmallfry

    rudysmallfry Feeling the Heat

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    There'e supposed to be a rise in the horizontal section? I didn't know this. Boy my installer sure did this thing as simply as possible. I'll have to check, but I think I can only shorten by about a 1' with the single wall, more with the double. Maybe I should shorten the vertical piece a few inches, open the 90 elbow up a bit to something like 110, and that would give a bit of a rise to the thimble. Is there a formula of how much rise per foot? Mine's about 3', I'd have to measure again for the exact. I'm at work goofing off right now.
  12. hearthtools

    hearthtools Moderator Emeritus

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    To answer the question about heat rating on some double wall. Here is ICC's Ultrablack rateings.

    Allowable Flue Gas Temperatures
    Max Continuous 1200°F
    Brief Forced Firing 1700°F
    Tested To 2100°F
  13. hearthtools

    hearthtools Moderator Emeritus

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    Thats funny 3 of us were asking the same questions at the same time but it took longer for me because I was chasing around my 21month old.

    what model I will let you know how close you can go?
    See my post about if you missed it.
  14. Todd

    Todd Minister of Fire

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    I think the rise should be 1/4" per foot. I would try cutting out that extra foot and see how she burns before spending big bucks on double wall pipe.
  15. MountainStoveGuy

    MountainStoveGuy Minister of Fire

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    Rod i agree completey, now that we have more information, the horizontal run with no rise, and the long horizontal run are a bad combo. You have plenty of rise on that chimney. If you can, get a little more rise per foot then recomended since you have that long run. You should see a significant improvement with that alone, if not switch to double wall, and as suggested, get that heat shield and move the stove closer.
  16. hearthtools

    hearthtools Moderator Emeritus

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    What Model of hearthstone??
    Do you have just Drywall on the wall or do you have a NFPA21 firebacking with airgap?
    Give us the info and we can tell you just how close you can get to the wall.
  17. elkimmeg

    elkimmeg Guest

    Rudy all prior suggestions are good advice. There is a cheap way to test out your theory first. The min pitch is 1/4" per ft
    the more verticle you make that run the easier for draft hot air and smoke to rise. That's why 2 45 works best you have a better upward path. The adjustiable elbows do not bent but both sides rotate changing the degree pitch of their angle.
    My syggestion is to setup your stove with the existing single wall adjustable elbows with the 45 degree pitch in place of that horizontal run and see if you have better draft. If it improves, which I think it will, Then you have other options like using fixed 22 gage 45degree elbows and pipe or even more expensive double wall connector pipe. To me it makes no sense to spend the money guessing it will improve your situation.
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