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Barometric damper

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by brickman, Feb 19, 2009.

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  1. brickman

    brickman Member

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    I am installing a Clayton 1600 furnace. I have been told by some people to use a barometric damper to control my draft, and others have said not to because it will lower your flue temp and cause more creosote. Can anyone give me some more information on these types of dampers?

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  2. pybyr

    pybyr Minister of Fire

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    Talk to the manufacturer and do what they say.

    Opinions as to what to do or not do with barometric dampers on solid fuel appliances are like a bad mix of politics and voodoo.

    I spoke to the manufacturer of my unit (Econoburn 150) and they said to definitely put one on, as the unit had been designed to work with one, that efficiency would be less without it, and that it would be safe.

    So I did.

    For my own peace of mind, I put it right at the place where the flue pipe from the boiler meets the chimney's vertical section. And I put it in a tee & elbow arrangement so that the damper is about a vertical foot lower than the run of flue pipe. That way any cooling effect does not take place until the combustion gases have made much of their travel, and are ready to go up the chimney, and since the damper is lower than the flue, backdrafting out the damper is much less likely.
  3. mtnmizer

    mtnmizer New Member

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    Anyone able to explain how to properly adjust a barometric
    damper? Mine has a sliding weight and and a scale
    of numbers. I have it set in the middle......I think some
    sort of instrument is needed to set it..
  4. ssupercoolss

    ssupercoolss Member

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    need to set it with a manometer. you can actually get one from grainger for about 30 bucks that will do the job. insert it in between the furnace flue and the baro. with a nice fire going adjust the baro until you get like .02 - .04, something like that. the manufacturer propbably has a recomendation on that. lots of info about baro's over at nepacrossroads.com (coal forum)
  5. pybyr

    pybyr Minister of Fire

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    Yes, you should set the damper up with a draft gauge-

    commercial draft gauges are expensive, but here's a great description of a DIY one that I copied and pasted from the YahooGroup "altfuelfurnace" (where they focus on converting standard-type oil burners to be able to run on used vegetable oil and other waste oils)

    <START QUOTE> :

    Construction details for the inclined draft manometer follow below:


    Most domestic boiler manufacturers specify .020" of water column vacuum
    "over the fire", or a slight vacuum close to that figure. Although
    draft gauges are made for measurement of low vacuum levels, an inclined
    manometer suitable for the purpose can be made at almost no cost.


    Since .020" of water column is hard to measure with a conventional
    manometer, make up one from small diameter glass or clear plastic tubing
    that is slanted almost to the horizontal. For example, make the rise 1"
    in 10" of length. I made one many years ago on a piece of plywood
    nailed to the wall. Connect a piece of chem lab rubber hose to the
    lower end (1/4" glass tubing in my case), and run it into a "well",
    like a 35mm film can also tacked to the plywood. Make the height of the
    well about half below and half above the low end of the manometer
    tubing. Connect the top end of the manometer to a longer piece of
    rubber tubing to reach the boiler inspection port. Pour the well about
    half full of water, suck gently on the long rubber tubing, and you will
    pull water in to the manometer tube by siphon action. If you fill the
    well about half full, the water height equilibrium in the manometer tube
    will be about halfway up the incline.


    The point of the incline is the following: 1" of rise in 10" of
    manometer tubing multiplies the sensitivity of the manometer by 10. If
    you draw .020" of water column vacuum at the top end of the manometer,
    the water meniscus will move up the tubing by .200", easy to discern.


    Put a piece of 1/4" copper tubing in the remaining end of the long
    rubber tube, and you are done. Insert the other end of the copper
    tubing into the combustion chamber inspection cover small hole. Move
    the damper counterweight by unscrewing just enough to move it, and
    position it to get the water meniscus to move upwards (vacuum pulls it
    up) by .200" in the example slant given. Take the sampling copper
    tubing in and out of the boiler port to confirm .200" movement of the
    water meniscus.
  6. pybyr

    pybyr Minister of Fire

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    If/ when, as with my Econoburn, the manufacturer specifically recommends it in the installation manual, and when I call up to check, they verify that, and say that the unit was designed to be most efficient _with_ the damper, then- even though I tend to be one to ask questions- I have to assume that they are doing this for something other than a random reason.

    I purposely "pause" my damper temporarily with a little weighted steel strap for when I am starting a fire or loading the firebox, so as to keep the damper closed and boost the draft temporarily at those times.

    As to quality of fire, I've played around with leaving the barometric damper blocked off during a main burn. Draft gauge (which I leave connected all of the time) goes way too high, flue temps go higher than makes sense for good efficiency, and I get less heat per unit time per unit wood than when I let the damper operate. You can hear the difference, too, of the fire whooshing through faster. Less time spent by the fire in the boiler's heat exchangers means less heat extracted from the fire.

    So- for appliances like low-tech devices where a barometric damper is specifically not recommended, well, don't use one!

    For units where the manufacturer recommends a barometric damper, or for high efficiency units like the gasifiers, don't let the apparent prevailing assumptions talk you out of it, as long as you install it correctly and set it up correctly! Hansson from Scandanavia, who visits the Boiler Room, confirms that barometric dampers are the norm on gasifiers there. Since the Scandanavians pioneered this technology, and are pretty methodical, and into efficiency, one has to assume that they're onto something...
  7. LeonMSPT

    LeonMSPT Minister of Fire

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    Have a New Yorker WC90 wood and coal boiler. Conventional "dutch oven" type water jacket boiler.

    Manufacturer recommended Barometric Draft Damper (BDD). Contractor doesn't like them on wood burners, period. I didn't either, for the same reasons. "If" there is a chimney fire, it will feed air to it and will not limit or control the fire at all. So, I had him install the boiler and connect it with regular old galvanized pipe.

    Here is what I've learned since:

    1. My chimney is 35 ft tall, 6x6 stainless liner, inside of an 8x8 double brick masonry chimney. When I first lit the boiler, it made tons of gross smoke... awful thick black stuff. It took what seemed like forever to come up to temperature. Gobbled wood and coal like it was going out of style. Reloads on wood every three to four hours. Reloads on coal every 5 to 6 hours. Numerous "puffbacks" and coal gas "explosions" occurred all the way from the boiler door to the top of the chimney. Blow dust and junk out of every crack in the pipe joints and shake that end of the house.

    2. Enter the education phase, when I begin to question what I was doing based on my results. Researched the issue here, and at NEPA. Coal users over there said, "No BDD, you're going to go through coal like it's going out of style."

    3. Creosote deposition depends on more than temperature alone.
    Particulate concentration is one issue. The higher the concentration, the more deposition, regardless of temperature.
    Stack velocity is another. The faster the exhaust is moving through the stack, the less deposition you will have. The slower it is moving through the stack, the more deposition, regardless of temperature.

    4. We all know that fire and combustion depends on three things. Heat for combustion, fuel to burn, and oxygen to supply the fire. If the unit is "airtight", and a chimney is pulling on the chimney stack at a rate five times the called for draft, it's trying to burn the fuel in a vacuum. Unburned gasses and heavy particulates are dragged out of the firebox and into the chimney before they get a chance to burn.

    5. When I added the BDD.

    Fire brightened in the firebox immediately. Smoke was lighter both in the firebox and coming out of the chimney.
    The boiler came up to temperature much faster. Wood and coal consumption went down by 30 to 40 percent.
    Stack temperatures went from 300 degrees at idle and 650-675 degrees at high fire, to 125 at idle and 425 at high fire.

    Loading without smoke running back into the room is no problem. I have the draft adjusted to 0.02 inches. If I open the door when there is a load of logs burning in there I get a face full of smoke and some fire. No helping it. If I need to open it in that situation, I jam the BDD shut with a pair of needle nose and open the door slowly. Never forget to remove the jammer and allow the damper to function properly. If I simply wait until the fire burns down to near coals, but still making heat, I open and close the door without any smoke in the house at all. Not even the smell of it.

    What is the end result?

    I piped the chimney connector with "T"s and end caps on the horizontals. Cleaning takes ten minutes from start to lighting the fire. I clean it whenever I see there is anything building up in it. Considering that the BDD absolutely dilutes exhaust from the boiler with fresh air that cools and reduces concentrations. If I am to have a chimney fire in this chimney, it will be because I had a chimney connector fire that spreads into the chimney. With the BDD in place, the highest temperatures in any burn cycle I have observed were 425 to 450 degrees a foot from the boiler. Not hot enough to autoignite creosote, and with the baffle plate in place and air adjustment appropriate on the combustion blower I do not get flame protrusion into the chimney connector. Needs service and maintenance? Yes. Anybody that minds service and maintenance shouldn't be burning wood or coal.

    With the BDD, the danger is "if" there is a chimney fire. Without it, the danger is "when" there is a chimney fire. Because with a solid pipe and no BDD, at least in my situation, it would only be a matter of time. Not to mention burning more wood and coal than necessary only to sweep the larger part of the heat out of the chimney and connector every two to four weeks all winter. And the misery I'd be giving my neighbors... which I am not now.

    Have some pictures if you're interested.

  8. laynes69

    laynes69 Minister of Fire

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    I have one. I found it lowered my wood consumption, and increased heat output with the unit. We have a large masonary chimney and we had an overdraft. High stack temps, and so so heat output with the woodfurnace. Now we have even heat, and better combustion due to the fire has a chance to burn everything up! They do make a difference. Just check your flue and chimney when needed and you won't have any problems.
  9. CrappieKeith

    CrappieKeith New Member

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    There's some good answers here.

    It's pretty simple really.A good drafting flue wants to run at .08"WC. A BDR will slow the draft.Set at .03"WC you should have a flue gas temp of 400-425 degrees.
    Allowing your unit to exchange heat is the idea.Smoke which is a gas will not condense at 400 degrees, but it is important to have a good flue to keep the stack temps up.
    Cycling burn rates will also give you longer burn times but set on an idle for too long can let the stack temp drop too much causing condensation.
    A manometer is the tool to read water column. Anyone burning wood should probally own one. Sure there's the ole eyeball trick,but why guess? Sorry that was rhetorical.
  10. Wood Pirate

    Wood Pirate Member

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    LeonMSPT I would love to see your pics if possible. I have a WC90 that I installed in the fall with a BPR but have to take all the piping apart to clean it.

    Thanks
  11. LeonMSPT

    LeonMSPT Minister of Fire

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    Make sure you've got plenty of draft, as the "T's" are "draft hungry"... so far it's working well. I clean it every other week or so, just to be safe.

    Attached Files:

  12. LeonMSPT

    LeonMSPT Minister of Fire

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    One small detail.

    I do not know of any maker of smokepipe that makes a "T" with two female ends on the straight, and the male on the side. Usually, it's male and female ends and female on the side.

    A little "surgery" with a drill and rivet gun solves the problem... :) Oh, when you rivet the female part back on... do it from inside out. You'll see why when you're doing it.

    (Put them outside in, and you can't slip the male pipe into the female outlet... ;) )
  13. CrappieKeith

    CrappieKeith New Member

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    Good post Wood Pirate....really good post.
  14. oldmilwaukee

    oldmilwaukee New Member

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    pybyr,

    thanks for posting the info on how to build a manometer - I'm going to the basement to build one just like it right now. I suspect the draft on my Tarm is _way_ too strong. (8x8 tile flue, 40 feet tall) I have a BDD on it now, but just guessing at the setting until I get a real reading.

    The instructions you posted... doesn't the # one gets have to be multiplied by two to get the real answer? Just wondering, based on what has been posted about U-tube manometers at the following links. I know the design is different, but still... I dunno.
    http://en.wikipedia.org/wiki/Pressure_gauge
    http://www.komar.org/faq/manometer/
  15. oldmilwaukee

    oldmilwaukee New Member

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    OK, sorry to wonder out loud, but I guess the # you read is the actual pressure, according to these fellows:

    scuba board
  16. pybyr

    pybyr Minister of Fire

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    As I understand it, you'd only multiply with the U-types, not with one that is a single tube
  17. pybyr

    pybyr Minister of Fire

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  18. oldmilwaukee

    oldmilwaukee New Member

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    thanks pybyr. I finally built something and measured my draft with actionable results....

    I ended up making a u-tube from a 3' piece of 1/2" clear pex (dug it out of the trash). nailed it to a 2x4 and put the 2x4 on a 45 degree angle, so the # I read was the actual number. stuck a 1/4" piece of fuel hose into one end of the Pex (fit perfectly), ran the other end of the fuel line to the hole in my flue that my stack temp probe usually occupies. Using a tape measure and squinting a lot, it looked like I have a "heavy 1/16th" (.07 or .08") of WC for my draft. When I let the barometric draft damper do its thing, I had a light 1/16th to a 1/32nd (.05 to .03) depending on where I adjusted the thumb screw. This was with the Tarm running full bore in gasification mode. I took my best guess at .04 and left it there. More squinting, bifocals, smaller tube, colored water, and a shallow incline would have made for more accurate measurements, but I just used what I had in the basement. In fact, I filled the u-tube with water bled out of the boiler. :)

    My stack temps are often 700 degrees, my HX tubes are clean, and I'm satisfied the draft is right, so I think it's time for turbulators.
  19. muleman51

    muleman51 Member

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    I've put a BD on my stack but I can't seem to get it adjusted. When I start the fire I get a lot of flopping and smoke and it seems to take a lot longer to get the fire to level out and quit stinking so bad. My stack temp runs in the 450-550 range so that seems about right and I do think it takes less wood although that is somewhat hard to access now that it is slightly warmer and only building a fire twice a day. All I do know is that it will fill my boiler room with smoke out the damper pretty fast before it quits flopping. I'd be dead if I had this thing in my house if not from the smoke from my wife , I wouldn't blame her either. I'm about ready to take it back out., but maybe someone has the answer on how to fix this. Thanks Jim
  20. LeonMSPT

    LeonMSPT Minister of Fire

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    Stack temperature is about right...

    Sounds like you're laying in a fire, lot's of wood on top of kindling and paper. Lighting it off, closing her up and letting her rip.

    Decent approach, but when the weather is warm and humid, most chimneys don't draw too good. When you light a fire, smoke and gasses accumulate and burn off "WHOOOF" and shoot smoke out the BDD and the vents in the door.

    I get around this by lighting a smaller fire with kindling wood, to heat the chimney up without producing huge amounts of water vapor and smoke. When that burns down to near coals but still open flames, I load the firebox. Big fire, no backpuffs...

    The flopping is a clue, it's going from negative to positive because the flow in the chimney isn't established yet...

    Leon

  21. muleman51

    muleman51 Member

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    The flopping seems to be the most when I add wood to a bed of coals. The wood seems to start to cook and make smoke before it flames. I burn mostly all rounds and use very little kindling only when I have very few coals.I'm very glad my boiler has outside air to the combustion damper so it doesn't blow smoke out there also.
  22. ohbie1

    ohbie1 Member

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    I agree with Leon on making a small HOT fire to get the draft going. I also use a small piece of magnet to hold the damper closed (actually the back of a small speaker), when I first light the fire. One more thing, when you light the fire, get the door closed fast. I noticed on my manometer that when you have the door open, the draft drops to zero. I now light the starter paper, and turn on the fan after I close the door.......no more smoke problems.
  23. Piker

    Piker Minister of Fire

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    In my experience with my indoor wood boiler, I have found, like others, that during the shoulder seasons, the draft in the chimney isn't all that great. This year I haven't used any thermal storage, and when the boiler comes out of Idle, I get a faint puff of smoke out of the barometric damper. It's not an issue because the smoke doesn't seem to come up into the living area, but draft seems to get better when I crack a window in the basement. I have not actually checked the draft to tell you what it is, but the puffing doesn't seem as prevalent.

    cheers
  24. LeonMSPT

    LeonMSPT Minister of Fire

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    Biggest snort I've had, short of a coal gas explosion which is a cat of a different color entirely but not totally unrelated... Loaded a monster load of wood in on top of a bed of coals... cool, but not "cold" out... kind of foggy.... smoldered awhile and then when it lit.... "PPHHHHHHOOOOFFFF" looked like I'd launched a rocket out of the chimney.

    Kind of need actual fire, and a hot stack, before you load it big...


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