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Harman Invincible burn rate problems

Post in 'The Pellet Mill - Pellet and Multifuel Stoves' started by kaynos, Feb 24, 2008.

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  1. kaynos

    kaynos New Member

    Joined:
    Feb 24, 2008
    Messages:
    2
    Loc:
    North Jersey
    I purchased an harman Invincible T model a few months ago. I have been trying to run this stove at high output and can't seem to get more than a bag every 11 - 12 hours. I believe I should be able to burn double that rate.

    The heat exchangers gets sooted up pretty fast (1 to 2 weeks) with light fluffy black ash. I've replaced the door gasket with 3/8" rope gasket, hopper gasket with some rubber weather stripping. I generally perform a full seasonal maintenance every 1 1/2 to 2 weeks but have yet to achieve a good burn rate.

    The unit is currently direct vented with 3" PV. 1 90 deg on the back of stove, 3ft section going up 1 90 deg to outside, with a 3' section. No cap currently.

    Originally the unit ran hot, and shut down on over temp when I first hooked it up.

    The unit was leaking air through the hopper door, front door, and a small leak in the cover gasket on the side of the auger in the back where the feed rate screw is.

    The main leak was the hopper gasket, causing too much air to enter and it overheated. I am unsure if the hopper in this model should be completely sealed off, which is what I've achieved with rubber weatherstripping.

    I've cleaned and checked the combustion motor several times.

    I've removed the burn pot and checked the gasket and cleaned it out.

    I'm at a loss as to what else I can check.

    I have noticed that the right hand side vent seems to run cooler than the left even when it's just been cleaned, and it gets worse as the week goes on.

    The right side glass also accumulates some black soot.

    I burn ~ 2 bags a day, every day and I can't seem to burn any faster.

    I'm very fustrated and don't know what else to check.

    Thanks for your time.

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  2. webbie

    webbie Seasoned Moderator Staff Member

    Joined:
    Nov 17, 2005
    Messages:
    12,384
    Loc:
    Western Mass.
    2 bags a day is a nice medium rate - about 28,000 BTU input and maybe 20,000 output. But the stove should be able to go higher, maybe up to 3 bags a days.

    My first thought is that your problem lies in air flow, which points to a number of possibilities.....guessing here:

    1. The venting - two 90 degree els and only a 3 inch rise - your vent restricts the air flow to some degree.
    2. Doesn't Harman have a draft adjustment which can be set with a draft gauge to assume proper air flow?

    These two things are related, because you need to push more air through the unit in order to burn more pellets. Also in order to have the over heat not go off.

    Was the unit professionally installed and set up with gauges as per Harman instructions? If not, can it be done?

    There are some Harman experts here and chances are you will get a more detailed answer, but my guess is combustion air flow.
  3. kaynos

    kaynos New Member

    Joined:
    Feb 24, 2008
    Messages:
    2
    Loc:
    North Jersey
    Thanks for your reply.

    The stove is rated at 55K btu. That would be nearly 4 bags a day from my math, but maybe it's not a real world scenerio.

    I have a 90, with a 3 foot rise, then another 90 to outside.

    There is a draft adjustment, but on my model, it sets the idle draft when you aren't calling for heat and the stove is in standby. I've verified the adjustment with a volt meter on the combustion motor.

    Instructions mention guages, but also state that generally it can be left alone and the instructions are from the idle perspective. I'm running full tilt..

    I've measured the voltage at the combustion motor, and I am seeing the full 120v when the feed motor is running.

    I have no trouble feeding more pellets than I can burn.. Generally 4 1/2 turns out from full stop is where I can burn. I've tried at least 5 brands of pellets.
  4. webbie

    webbie Seasoned Moderator Staff Member

    Joined:
    Nov 17, 2005
    Messages:
    12,384
    Loc:
    Western Mass.
    Right, still points to air flow. If you can feed more pellets than you can burn....that points to lack of combustion air to burn them.

    The factory may mention it can be left alone in many cases, but consider that most folks burn 1.5 bags a day. So they rarely, if ever, run up against your problem.

    The stack represents a serious "impedance" to the air flow. Just for illustration, with a wood stove a 90 degree bend is considered to take 5 to 6 feet off the effective height of a chimney. Horizontal sections also impede draft. So take 12 feet off the total height of your chimney....and we have MINUS something feet. Yes, as you see, a pellet stove can overcome this to some degree, but not totally.

    Exactly how you fix this is more for a Harman expert (and there are many here), but generically:
    1. Larger pipe size has less flow restriction
    2. Taller pipe system can help draft, especially if you remove on el
    http://www.hearth.com/econtent/index.php/forums/viewthread/13419/#148730

    3. Adjust gates, dampers, etc. to allow for more air flow.

    Other factors are related more to your specific stove, control board, sensors, etc.
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