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Thelin Gnome & Carbon Monoxide - trouble-shooting

Post in 'The Pellet Mill - Pellet and Multifuel Stoves' started by Andrew Robinson, Feb 4, 2013.

  1. Andrew Robinson

    Andrew Robinson New Member

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    Good morning,

    I have a 4 year old Thelin Gnome pellet stove installed in a 40 foot boat. I use a pipe to bring in outside combustion air. The heated space is quite small ~200 sq ft, but the stove is on low all the time because it is minus 40 outside. (I'm in the Canadian arctic) I have a ventilation fan that gives me about 1/2 an air-change per hour.

    EDIT - I'll add extra info here based on people's responses:
    - I do not operate other combustion appliances (like propane)
    - The stove has a combustion air duct connected to the outside
    - the fresh air (for breathing) comes in around the door
    - I've measured the CO content of both the combustion air and fresh air & they are zero ppm

    A few months ago my carbon monoxide alarm went off and I had to move out because it is my main source of heat. (an electric heater can keep things just above freezing)

    have been trying to fix the problem for over a month and cannot find what is wrong.

    The alarm does not go off, but I have a Testo 327 combustion analyzer & CO meter and can watch the levels creep up - it gets to 40ppm after 8 hours of running on low.

    So here is what I have tried:
    1 - sealed all chimney joints, seams and connections with high temp silicon
    2 - replaced gaskets on door and window glass
    3 - re-sealed combustion fan plate with 2000 deg F fireplace cement

    Questions:

    1 - there is space around the fan shaft - through the plate that keeps the hot gases separate from the ventilation air - is this normal? I imagine that the fan will create a suction effect that "should" prevent gases from escaping, but perhaps some manage to get out?

    2 - is it just "normal" for a pellet stove to emit some CO? Am I just using it in too small of a space?

    Any advice would be greatly appreciated!

    Andrew

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  2. begreen

    begreen Mooderator Staff Member

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    Have you checked for other possible sources of CO like a propane cook stove? Are the pellet stove fumes being sucked into the fresh air intake? Maybe try adding a length of stove pipe to see if that mitigates the issue.

    Also, are there any neighboring boats burning wood or pellets whose fumes are getting pulled into the cabin?
  3. seige101

    seige101 Minister of Fire

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  4. begreen

    begreen Mooderator Staff Member

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    Correction, they ARE expensive. A boat is a hole in the water that you pour money into.
  5. Andrew Robinson

    Andrew Robinson New Member

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    Thanks for the ideas.

    I do have a propane cook-stove, but it is not in use when I get the CO - it is directly related to the pellet stove. Light stove, CO goes up. Stove off, CO goes down to zero. No neighbours either.

    Andrew
  6. Andrew Robinson

    Andrew Robinson New Member

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    Just in talking to Thelin today - all their units have a gap around the fan shaft - so that should not be the problem.
  7. Mdw1219

    Mdw1219 New Member

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    Is your fresh air intake near the exhaust from the stove pipe on the exterior?
  8. Ricks

    Ricks Member

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    I would spend sometime checking your battery charger and the condition of your batteries. It is my understanding that a battery that is being overcharged will give off a gas that will trigger a CO alarm. Given you are using the stove on a boat I would make sure my battery compartment is vented to the outside and not the bilge or cabin.

    Rick........
  9. Andrew Robinson

    Andrew Robinson New Member

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    The fresh air is pulled in around the door. It is somewhat sheltered from the chimney. I have thought this might be the issue, but even when the wind is blowing smoke away from the door, there is still a CO issue.

    Unless CO behaves differently from the rest of the exhaust gases?
  10. Andrew Robinson

    Andrew Robinson New Member

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    Thanks for the idea - but the batteries are in the engine room - behind a weatherstripped door & vented to the outside.

    Andrew
  11. Andrew Robinson

    Andrew Robinson New Member

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    Very interesting thread - similar story to mine. I also wonder how long I have been living with low CO levels without setting off the alarm.

    And I can verify the "hole in the water you throw money into" story ... add "time" as well - that hole in the water sucks up time as well as money!
  12. wwert

    wwert Feeling the Heat

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    Is it possible your outside air intake is sucking in the stoves exhaust?
  13. Andrew Robinson

    Andrew Robinson New Member

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    I was just thinking about that, but the answer is "not possible".

    I'm using a Testo 327 combustion analyzer to measure the ambient CO. It has a probe on the end & I've measured the CO levels in the air coming in the combustion air vent and in the air just around my door where the air comes in. All outside air readings are zero and the levels start going up as soon as I move the probe away from the fresh air.

    Andrew
  14. Shaw520

    Shaw520 Feeling the Heat

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    You need a outside air intake dedicated directly to the stove,... if you are relying on air being drawn in through door crack to supply the stove in may not be sufficient. A 2" flex pipe should feed direct from outside air to the stove's intake pipe.
  15. Andrew Robinson

    Andrew Robinson New Member

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    Sorry - I was not clear. Combustion air comes in through a duct - as you describe. Fresh air - for breathing - comes in around the door.

    Andrew
  16. Mdw1219

    Mdw1219 New Member

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    Is it possible you fan brushes are going bad? The gnome has a dual function fan that has two fans attached to one motor for intake and exhaust. If the fan brushes are going bad you will notice the fan speed fluctuating up and down, end result is not enough to force the bad gases out the vent properly. Also on the control board there are to fan setting dials that allow you to increase the fan speed low and hi maybe by increasing them slightly it will force the exhaust out better.
  17. Andrew Robinson

    Andrew Robinson New Member

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    Interesting idea ... the fan appears to be working well enough, but the CO levels do go down by a couple ppm if I run it on medium speed. Running on medium or high does not solve the problem, though.

    I currently suspect the joint between the cast Aluminum assembly on the front of the stove and the main body. It has a ribbon gasket that might need replacing. Not sure how to dis-assemble that, though it is about the only thing I haven't dis-assembled and re-assembled!

    Andrew
  18. moey

    moey Minister of Fire

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    I found this interesting, I assume you don't smell smoke?

    I always assumed with a pellet stove if you had CO you would have some smoke that you could smell as well. Thats a pretty clean burn if you don't get smoke with CO.
  19. Andrew Robinson

    Andrew Robinson New Member

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    There might be a very faint smell of smoke - more like "hot metal" if you know what I mean.

    My home - a boat - has a very small volume and a low ventilation rate - about 0.25 air changes per hour through the composting toilet fan.

    So I guess even a very small leak can have an effect - where in a larger, leakier house, it would never be noticed.

    A
  20. Andrew Robinson

    Andrew Robinson New Member

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    I did find and seal a very small potential leak in the connection between the pellet stove and the chimney.

    And I sealed around the combustion gas fan with hi-temp silicone - it looked like the hi-temp cement may have cracked along the gap between the fan mounting plate and the exhaust port.

    For a few hours, I had excellent readings of no more than 3ppm which declined to 2ppm. But then, in the morning, the readings on the Testo analyzer were at 90 ppm! My other standard, $40 CO detector read "zero" for another half an hour and then it eventually showed readings of up to 22ppm (the stove was already off by then)

    It is clear that $40 CO detectors are not accurate at low concentrations - if you read the fine print, they even state that they do not work well below 30ppm and below humidity of 20% (in cold weather, our indoor humidity can drop below 10%). But I would expect the Testo to be more accurate.

    So I'm back to 3 options:

    1 - the gap around the fan shaft
    2 - unreliable CO detectors creating false readings - very consistently
    3 - exhaust being sucked back in through the door - although I measure the air around the door with the Testo when I zero it - it did give me a "CO detector is unstable - resample" error once while doing this

    I'll keep trying to let you know what I find.

    A

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