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  1. RJ Schulz

    RJ Schulz New Member

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    I have a new Jotul C350 fireplace insert that was installed by the dealer. When not in use with the air flow lever fully to the left (closed) I am getting a strong draft out of the lower vent where the fans are located. This does not seem normal. I have the face of the insert covered with a magnetic cover to reduce the draft, but it still lets in a lot of cold air. What could be the problem?

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  2. Fod01

    Fod01 Feeling the Heat

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    Some random thoughts without knowing anything about your setup.....

    Assuming that you had a liner installed, was there also a block-off plate installed? This fills the gap between the old flue opening and your new liner. I dont have a proper plate. I shoved some rockwool in the opening. Makes a difference.

    There should also be a plate at the top of the chimney where the liner exits.

    Please provide some details, and welcome to the forum
    Gabe
  3. mellow

    mellow Resident Stove Connoisseur

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    Sounds like air is coming in via an Outside Air Kit that is hooked to the insert, if that is the case then I would look into finding a damper to install to cut off the air when it is not in use.
  4. Jags

    Jags Moderate Moderator Staff Member

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    OAK - could be coming in from there if one is installed.
    Down Draft - you could possibly have a negative pressure situation causing air to come down your pipe
    Block off plate - if one was not installed, it could allow cold air to travel down to the body of the stove and out.
  5. TradEddie

    TradEddie Minister of Fire

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    I'm always surprised by comments like
    Almost everyone will have negative pressure when the stove or insert is not running, and with an exterior walled chimney, the potential for downdraft. Since EPA stoves inherently cannot fully close the air supply, unless you have an airtight flue damper, there must be some draft of cold air if the insert is not running. What surprises me is that more people don't notice this. I do.

    Despite this, it is more likely that this is not the significant cause of your detectable draft, a block off plate will help, as will ensuring that the top plate is sealed too. I also suspect that in some cases there can be what I call "convection draft", air in the convection passages cools and sinks, drawing air in the top and out the bottom, reversing the direction of the normal convection currents and creating a draft, even if the air is not coming from outside. This might be reduced by block-off plate, but only insulating the old fireplace would really fix it.

    TE
  6. Jags

    Jags Moderate Moderator Staff Member

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    I don't buy it. Warm house, cold outside, air should have a tendency to move out not in unless you have something generating a negative pressure in the house like a power vent water heater or a dryer or vent hood, etc.
    webby3650 and Heatsource like this.
  7. TradEddie

    TradEddie Minister of Fire

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    The stack effect is going to cause the lower level of any building to be at lower pressure than the outside air. Maybe not noticeable in a ranch, but very obvious in anything with two or more floors. Don't believe it? Crack open a downstairs window, feel the draft, then open an upstairs window the same amount, air goes out. Makes air leaks upstairs almost impossible to find.

    TE
  8. Jags

    Jags Moderate Moderator Staff Member

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    You have just explained why air will go out of the pipe, not in. If a stove was at a static state of downdraft you would never get a fire lit without smoking the home out. Unless of course you were to preheat the stack. This is the exception, not the rule.
  9. TradEddie

    TradEddie Minister of Fire

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    One of us is missing something. Air pressure downstairs in a multi-storey house is lower than outside so air from outside wants to come in. The stack effect is not because of altitude, it's the same effect that creates a draft when we light a fire, hot air rises and escapes, drawing replacement in below. A cold chimney does not generate draft in either direction, just facilitates the flow of air from high pressure outside to low pressure downstairs. You don't need to preheat the flue to overcome the stack effect, the heat from kindling will easily do it most times.

    Obviously there are other factors at work, because some people always have smoke problems on startup, others swear they have never seen it. A badly air sealed house will reduce the pressure differential, maybe that's why some don't notice anything.

    TE
  10. Jags

    Jags Moderate Moderator Staff Member

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    Flow = draft. Fluid dynamics at work. You cannot have flow of air without a draft being present. It would be like saying a garden hose is only the conduit so that water can move from end to end without flow - impossible.

    Place a candle in your stove (cold/steady state), right at the opening where your handle is. Crack the door slightly. Does the flame move towards the center of the stove, or towards the door? That will answer the question of which direction the pressure difference is moving. (mine will actually suck the flame towards center and put it out.)
  11. webby3650

    webby3650 Master of Fire

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    That's simply not true. You might have this problem in your home, but most do not.
    Of all the fireplaces and stoves that I clean, (EPA, masonry, or pre-fab) I rarely have a down draft while cleaning it. I sweep a lot of flues from inside, most of the time, the soot is being pulled up the flue, even with a brush in it. When we are installing a new flue system, I can feel the draft in the flue before the stove is even hooked up. If I couldn't, I would be worried.
  12. TradEddie

    TradEddie Minister of Fire

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    In your hose analogy, the question is what pumps the water? A cold chimney does not GENERATE flow, so what is driving air up your chimney when the stove is cold, when the stack effect should be drawing it down? I can say for sure that my chimney drafts down when cold, no wind, no central air, no dryers or fans. So did the chimneys in every other house I've lived.

    Maybe a freestanding stove is different to an insert in this way, perhaps the warm room heats the air inside the stove or stovepipe creating upward draft? Uninsulated liner in an interior wall would also help.

    Got to go do some work.

    TE
  13. webby3650

    webby3650 Master of Fire

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    I will guess that this insert is in a Pre-fabricated fireplace? (sheet metal)
  14. TradEddie

    TradEddie Minister of Fire

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    I'm just looking for an explanation for the source of this updraft.I believe you all, I just don't understand how its happening.

    TE
  15. Jags

    Jags Moderate Moderator Staff Member

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    Temperature differential generates the flow. That is why it is easier to get a strong draft going when it is very cold outside.
  16. TradEddie

    TradEddie Minister of Fire

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    Yes, metal fireplace in an uninsulated semi-exterior wall. I guess the cooling of the metal generates a draft that works with the stack effect to overcome the room heat inclination to go upwards.
    My insert is much colder than the room it's in. Insulating that wall, and filling the "heatilator" chambers with Roxul is an ongoing project that will never see complete success.

    TE
  17. RJ Schulz

    RJ Schulz New Member

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    Good questions. The installer shoved rock wool around the new flue pipe where it enters the old one. He also filled the cavity around the insert to fill the space in the old pre-fab. And there is plate at the top of the chimney. There is no draft around the sides of the insert, just the lower grille.

    Other info: the insert is cast iron. It is installed on the lower level of a three story condo. The chase is on the exterior side of the condo. And I do have a furnace with a blower for the exhaust. But this problem exists even when the furnace is not running. The draft might be stronger when it is running. The problem is most noticeable on very cold and windy days. A common thing here in lower MI.
  18. webby3650

    webby3650 Master of Fire

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    That's what I thought. I would guess that outside air is being pulled down around the outside of the inner flue. This passage is used to keep the pipe cool, it allows air to pass through freely. Since it's in a basement, you are getting a down draft of outside cooling air. Have you tried opening the outside air for the fireplace?

    This seems like the same problem was being discussed in another thread. Is it? I was PM-ing someone about this same senerio.
  19. RSNovi

    RSNovi Feeling the Heat

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    I was the one talking with webby. Mine has a significant cold draft while burning. I haven't really noticed it while not burning.

    I have heard a few people talk about the triple wall chimney having an outer layer for keeping the chimney cool. How would this air enter the house?
  20. webby3650

    webby3650 Master of Fire

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    Hey, there you are.
    The outer air jacket is open to the outside air, as part of the cap. It is also open on the top of the fireplace, this air could come out around the ZC box.
  21. RSNovi

    RSNovi Feeling the Heat

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    I didn't realize that the outer pipe chamber was open at the top of the stove. Is there any way to minimize the air reaching my living room?
  22. velvetfoot

    velvetfoot Minister of Fire

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    I am thinking it is the outside air for the fireplace. I plugged it and it was good. It was on the outside of the chimney.
  23. TradEddie

    TradEddie Minister of Fire

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    This what completely confuses me, if air has a reason to come down the outside of the flue, why do so many people find it so hard to believe that air will come down inside the flue - both passages start and finish in the same place?

    TE
  24. Jags

    Jags Moderate Moderator Staff Member

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    It is possible TE - but that is the exception, not the rule. Yes...some people get a reverse draft. You have been here long enough to witness the posts about "smokey startup", "smoked out my house"...that is what is happening for a good share of those types of posts, but again...it is a small percentage of those lighting their stove, often caused by an external force. High winds coming over the peak of the home, power vented devices in the home, etc.

    The "crack a window" solution or "heat the flue" is often the response. This does nothing more than getting the flue drafting in the proper direction.
    webby3650 likes this.

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