Overdraft and barometric damper on a Napoleon HMF200 / Continental CHMF200

Caydel Posted By Caydel, Dec 7, 2018 at 9:34 AM

  1. Caydel

    Caydel
    Member 2.
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    Oct 3, 2011
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    Loc:
    Ontario, Canada
    Hi all!

    Last summer, I had a Continental CHMF200 wood furnace installed. Continental is Napoleon's sister brand - this furnace is identical to the Napoleon HMF200 with the exception that some things are optional on the Continental instead of standard as on the Napoleon.

    Anyways, last year, we went through a ton of wood, and I suspected I had a problem with the stove. My burn times were poor (2-3 hours), we went through a ton of wood, I had high chimney temps etc. Given the height of the chimney (probably 30-35' from the furnace vent to the top) and our high winds, I figured it was a draft issue.

    This year, I installed a manometer (a Dwyer Mk II Model 25) to monitor my draft, and I definitely have a signifigant overdraft.

    The manual for the stone calls for an operating draft between -0.04" and -0.06", with lots of warnings that draft should never exceed -0.06".

    Now, I've been measuring the draft for the past week since I installed the manometer, and I'm seeing the following:

    0C (32F) - still air - draft between -0.08 and -0.10. Flue temp ~400F
    0C (32F) - slight breeze - draft between -0.10 and -0.13. Flue temp ~450F
    -9C (15.8F) - still air - draft between -0.12 and -0.15. Flue temp ~525F (right now)

    It gets a whole lot colder and a whole lot windier here as we get into winter proper.

    Now, the manual does allow for a barometric damper, but with a list of warning including rapid creosote buildup and uncontrollable chimney fires :eek:

    So, at this point, I'm looking for some advice. Should I install a barometric damper and just be prepared to check the chimney every few weeks? Should I just accept the loss of efficiency and high flu temps?

    Does anyone have any rough idea how much a barometric damper will cool stack temps? I know my wood this year isn't *great*, so stack temps are cooler than they would be with 'proper' wood. However, I also ordered two pallets of ecologs, which will obviously burn *very* hot to mix with my less than stellar wood.

    Seems that either way, I'm at risk of a chimney fire if I don't stay on top of the creosote buildup.

    On another note - the only way to clean the chimney is from the bottom inside our utility room, which is a hugely messy proposition. I'd like to be able to keep to cleaning once per year. If the barometric damper means I need to clean several times per year due to cooled stack temps... I'd almost consider just eating the cost of extra wood!
     
  2. wood butcher

    wood butcher
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    Jan 16, 2011
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    Loc:
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    I have a very simular set up and often wonder if I am loosing too much heat up the chimney. I haven't doen anything about it as overall I'm pleased with what I have but improvements are always welcome.
    I'm in Perth county and we have high winds from Lake Huron so we never have a lack of draft.
    I've just discovered cracks in the welds in the firebox on the part that takes air from the front of the furnace to the secondary tubes. Out of interest do you have anything that shields the corner welds, top left and right just inside the door?
     
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  3. velvetfoot

    velvetfoot
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    Dec 5, 2005
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    Now, hopefully someone will chime in that knows something. :)

    You could put in a barometric damper and see how things shake out. If worst came to worst, you could maybe take it out and put a blank in its place, or otherwise deactivate it without doing a bunch more work.

    Assuming you don't have the oil burner option?

    There's no forced draft fan with this heater...just natural draft.

    Do you have the outside air setup?

    The manual seems to say that secondary air comes from inside the house, but maybe not.
    (Note that secondary combustion air enters through two inlets on the front of the furnace either side of the ash lip tray and is not adjustable).

    My personal opinion is that these things are designed for some norms, and regulations, and if you're outside of the norms, like high draft, it's not good. I found a way to limit the air intake on my wood stove to control the raging secondaries, and it works great now, but it's a wood stove, not a furnace.

    Maybe contact the manufacturer?

    Good luck!
     
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  4. Caydel

    Caydel
    Member 2.
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    Oct 3, 2011
    26
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    Loc:
    Ontario, Canada
    I don't have the oil burner option, though I have a Continental propane furnace as the backup. My wood furnace is in the 'Add On' configuration.

    Yes, I have the outside air kit installed. Secondary indeed comes from inside the house, via two ports in the front face of the stove that are not adjustable. The draft really is the thing that controls combustion on this stove, and it's way too high.

    As it is, I hate the primary air control design as it's back asswards. It's run 100% by the thermostat - if the thermostat is calling for heat, the primary air is wide open. If the thermostat is *not* calling for heat, it's closed. So, in effect, you only get efficient secondary burn if the house is already hot enough. If you have a cold house, it will run the primary wide open until it's satisfied, which from my observation gives me no secondary burn, but 800 degree flue temps and a firebox burn down time of 1 hour. There is a high limit switch that shuts the primary air intake if plenum temps get above 250 degrees, but I've never seen that kick in, as the blower keeps the plenum sufficiently below that level.

    In practice, I keep the thermostat low all the time so that the primary air intake wants to stay closed, then manually block it open long enough for the stove to get up to temperature before I let it close down to encourage secondary burn.

    Now that I have numbers for the draft, I've contacted the contractor who installed the furnace to see about what we can do. It shouldn't have been installed in such a way that the draft runs 2-3X the maximum allowed in the manual.

    I want to get the draft situation resolved before I complain too much about the rest of the design - it might be that everything I dislike about this furnace works better when it's not being run harder than designed.
     
  5. Caydel

    Caydel
    Member 2.
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    Oct 3, 2011
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    Looks like mine has a reinforcing plate of some sort added. I feel now like I need to unbolt it to look for cracks...
     

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  6. brenndatomu

    brenndatomu
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    Aug 21, 2013
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    I would...in a heartbeat. You've got to get that draft under control, you are overfiring the furnace, and that leads to cracks, and poor efficiency, as you already know!
    If they are so dangerous why do many manufacturers require them? Heck, some even come with them! Now it is true about the chimney fire thing, to some degree...but if you burn dry wood, and keep your chimney clean, very little risk of a fire.
    Buy a Sooteater...do a bottom up cleaning using the plastic over the cleanout hole, with a shopvac stuffed in a hole through the plastic...not messy at all.
    Another neat trick I've seen is to cut the bottom off a milk jug, stuff the sooteater through the hole, again, shopvac taped into a hole in the milk jug.
    Only enough to get the draft down to your preset #...in other words, the draft goes high, the baro opens, cools the gasses a bit, draft drops, baro closes...so on and so forth...only it happens so fast that the baro doesn't really open and close...just kinda flutters gently...more so when its windy.
    In my opinion, you will get the most buildup right after the baro because that's where the air is the coldest...once it mixes with the hot gasses from the furnace, it will warm back up some.
    Many wood furnaces have this same issue...you need to visit the link at the bottom of my post...look through the glossary where it talks about the temp controller hack...go to the big Tundra thread and learn how to do it. It basically utilizes a programmable temp controller to overide the Tstats call for heat as long as the flue temps are within range...or you do as many of us have, not use a Tstat, just install a bath fan timer to call for heat long enough to get the firebox up to full temp, then just let it go...kinda like a manually operated stove. It works really well as long as you have dry wood!
     
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  7. Caydel

    Caydel
    Member 2.
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    Oct 3, 2011
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    Loc:
    Ontario, Canada
    Ok, the Sooteater looks amazing! Of course, I've already spent the same amount on a manual brush and rods... but the milk jug idea seems like the trick to do it much cleaner.
     
  8. wood butcher

    wood butcher
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    Jan 16, 2011
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    Thanks for the picture.
    I think that is what I am getting sent from Napoleon. I don't see how that will seal a cracked weld but I will see what I get. If it wasn't for the warranty I would grind and reweld it then put the plate on.
     
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