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2 wall stove pipe not as efficiant?

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by cruise1521, Dec 25, 2011.

  1. cruise1521

    cruise1521 New Member

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    We had about 6 feet of single wall pipe running from our wood stove to our double wall stove pipe chimney that runs through the upstairs. The single wall pipe worked well and radiated a lot of heat back into the room. Well when the owner of the company whom installed the pipe came out he realized we were 2 inches short of the 18 inch clearance for the single wall pipe. The only place clearance was an issue was the first foot up near the ceiling because of a bump-out ceiling molding. Anywho, instead of just running the 2-wall pipe that has a 6 inch clearance (think it is a single wall with a heat shield, not sure technical name for it) only down a foot from the ceiling where the clearance was an issue then continuing the rest of the way with single wall, they ended up running the 2-wall pipe ALL THE WAY down to the wood stove. Now I am finding the wood stove doesn't put off nearly as much heat as it used to with the single wall stove pipe. Will a 2-wall pipe really have that much of a difference when it comes to radiating heat that I would notice it when heating our downstairs. It used to get up to 78 degrees down here within an hour, now it seems to be struggling to even maintain 72 degrees after hours of burning and re-loading with wood.

    any input would be very appreciated.

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  2. oldspark

    oldspark Guest

    This subject can be a can of worms, (many others in the world of wood burning also) and you will see different opinions, but yes it makes a difference and you are one of the first to post a good comparision of the two ways so your results are worthy of noting. They possibably could have put in a heat shield in the problem area and saved you some money and your heat.
  3. firefighterjake

    firefighterjake Minister of Fire

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    I suspect single wall pipe radiates more heat than a double wall pipe . . . but that said . . . with doublewall pipe in my home and an Oslo I have no problem getting the temps into the mid to high 70s. I get the bulk of my heat out of the stove, not the stove pipe.

    It may sound stupid, but could you tell us about how you adjust the air control . . . please bear with me if I sound stupid . . . but some folks don't realize that by cutting down on the air you actually get more heat from your stove as less air goes up the chimney . . . some folks assume more air = more heat . . . with single wall pipe running the stove in this fashion would result in a lot of heat going up the chimney . . . and you would have a lot of heat radiating off the single wall . . . running it in this fashion with double wall pipe would still result in a lot of heat going up the flue, but you may not see as much of a heat gain.
  4. begreen

    begreen Mooderator Staff Member

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    It seems like we may be missing something here. Double-wall pipe still radiates a lot of heat. I suspect there is another variable that may be affecting the situation, but we need more information. What is the stove? Was it recently cleaned? Is this a basement installation? What are the outdoor temps? Has the wood supply changed?
  5. jeff_t

    jeff_t Minister of Fire

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    Also depends on what stove you have. An old smoke dragon could send a lot of heat up the pipe and you would benefit from it. More efficient epa stoves have much cooler flue temps and can benefit from the double walled pipe keeping the heat in, helping to maintain a good draft.

    What stove do you have?
  6. spirilis

    spirilis Feeling the Heat

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    Jake hit the nail on the head imo... Having insulated pipe (double-wall does offer some measure of insulation value I think?) for that whole flue should increase the draft too, and if the air settings aren't being turned down for sustained burns it's possible even more heat is going up the chimney now than was before, only most of this is ending up outside rather than radiating inside. If the chimney is very tall it might be worth getting a manual pipe damper in that double-wall (if they have ones that fit into such pipe) per the thread the other day (see http://www.hearth.com/econtent/index.php/forums/viewthread/86539/)
  7. firecracker_77

    firecracker_77 Minister of Fire

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    I run double for 13 feet, then another 13 approx. of triple to the cap. I agree that single would radiate better, but double ensures higher internal flue temps which will help with drafting especially during shoulder season when it's not as cold outside. The other advantage of double is that you don't have to worry about a little one scorching the crap out of their hands if they touch double. I never really thought about all the more usable heat you'd get from single, but I think having double is worth it too if the flue stays hotter and builds up less soot than if the temps drop too much by the top of the stack.

    Even my little gas Woodstock at home has double wall Duravent recommended by the factory. That is certainly an application where single would make more sense, but that's what Woodstock sells.
  8. cruise1521

    cruise1521 New Member

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    The wood stove is a Bosca Spirit 550. It is EPA approved and has the baffle (think that is what it is called) that burns the gases before going up the stove pipe. I do turn the damper right down, as I always did before. Nothing has changed except going from single wall to double wall. I'm even using the same wood as before. The temperatures outside are the same as they were a week ago when I had the single wall.

    Thank you for all the input!
  9. begreen

    begreen Mooderator Staff Member

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    How long has the stove been running since the new pipe? Just a guess, it could be that the stove size is a bit too small. When the space has been allowed to cool down, it can take a long time to bring the walls, furniture, etc. back up to temperature. Is the stove in a basement or on the first floor? If a basement or if the walls are concrete block, stone or brick, they will soak up a lot of heat. Six degrees is quite a lot, though at least 72F is still pretty comfortable.
  10. tcassavaugh

    tcassavaugh Minister of Fire

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    i would have put in a heat shield....piece of tin and some washers for spacers giving it some air space behind it. that way i could have kept the single wall heating the house too. i run single in the living space in the living room and family room and double wall for the thimbal through the wall in the rec room and up through the cealing in the living room.

    jmho

    cass
  11. cruise1521

    cruise1521 New Member

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    We have a raised ranch, the wood stove is on the first floor. There is no basement and there is one floor above us. When they switched the pipes out we didn't have a fire for only 5 hours, temp only got down to about 63 degrees in the house (35 degrees outside) when they were done installing the doublewall. Then we fired the stove up again. It has got to be the pipe difference that is making such a huge difference because nothing else has changed. I am going to call the company back monday and try to get them to switch it back to single wall.

    Even when we had got back from vacation about a month ago, the inside of our house was down to 48 degrees and we started the fire right up and the down stairs was in the high 70's within a couple hours. That was with the single wall...

    Now with the doublewall we struggle to keep it at 72 degrees downstairs after hours of burning. Yes, 72 is nice but not when you are used to it being 78 or higher under the same conditions. Because now the issue is upstairs is cooler too because downstairs is only at 72. Where before we never had an issue upstairs because it would remain right around 70 up there.

    It has to be that the single wall pipe was just always radiating a lot of the heat too, which helped out greatly with heating. Pipe temperatures of the single wall were usually always between 400 and 550 degrees at the base of the single wall pipe. So 6 foot of 400 degree pipe offered a lot of heating. Obviously the pipe was cooler near the ceiling but still...
  12. HotCoals

    HotCoals Minister of Fire

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    It will make a diff.
    Blaze King says I should have double,but I don't (help keep flue temps up).
    Double would be fine for me during the shoulder season but when it's really cold I want that extra heat from the single.
  13. EatenByLimestone

    EatenByLimestone Minister of Fire

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    The single could have really helped push convection currents around also. As the air warmed up going over the pipe it would have really started moving around.

    Have your burn times changed? Longer/shorter?

    Matt
  14. firecracker_77

    firecracker_77 Minister of Fire

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    Sounds like you know what has to be done. Get that single wall back.
  15. HotCoals

    HotCoals Minister of Fire

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    Good thought. cheers!
    I have way more natural moment of air then I thought I would have.
    I hung two ft. strips of toilet paper from the middle of door ways.
    Interesting experimenting with some doors opened..some close and then trying the fans on the stove while watching the strips.
    Also held a strip near the bottom of door ways to watch the cold air return to the stove room.
  16. begreen

    begreen Mooderator Staff Member

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    Well, the easy way to find out is to return to the single-wall pipe with a pipe heat shield on the top section. Maybe the stove is just quite inefficient and allowing a lot of heat to go up the pipe? FWIW, a normal single wall surface temp on the flue pipe when a modern EPA stove is in secondary burning mode would be about 300-400F. The normal surface temp of double-wall in the same circumstance would be about 150F-250F. I leave it up to the engineers to translate that into btus of heat radiated.

    Question, do you run it with the blower on or off?
  17. HotCoals

    HotCoals Minister of Fire

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    Going to be some exponents and correlations coming up..need to grab me a snack! lol.
  18. begreen

    begreen Mooderator Staff Member

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    LOL, I'll bring the popcorn.
  19. Todd

    Todd Minister of Fire

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    I think I read it was a 10% increase in heating efficiency with single wall verses double wall? But there's limitations length wise where it starts reducing your draft and effects the efficiency of the stove.
  20. cruise1521

    cruise1521 New Member

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    thank you for all the replies. To the person whom asked if we use it with the blower on or off, we have not purchased the blower for it because we never needed it when we had the single wall pipe. It always radiated and circulated heat just fine. Obviously a blower would have probably given it an extra boost though.
  21. oldspark

    oldspark Guest

    IMHO if you only have 6 ft or so of stove pipe the double wall is not going to help the draft that much, no way would I spend the money for my setup with only 5 feet on stove pipe.
  22. HotCoals

    HotCoals Minister of Fire

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    I concur with you.
    I know the heat off the single really helps in the deep freeze.
  23. woodmiser

    woodmiser New Member

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    But... if you have a damper half way up it goes a long way at keeping the lower half of the pipe hot. Trust me.
  24. firefighterjake

    firefighterjake Minister of Fire

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    Good to know it's not the wood or the way you're running the stove . . . but there has to be something going on . . . as I said . . . I have double wall and the temps in the room with the stove are always in the mid to high 70s and in the low 70s to high 60s as you move to the adjoining rooms.
  25. ddddddden

    ddddddden Minister of Fire

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    Air leaks in the new pipe joints?

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