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Wood pellets...pellet size matters

Post in 'The Pellet Mill - Pellet and Multifuel Stoves' started by ChrisWNY, Feb 13, 2012.

  1. ChrisWNY

    ChrisWNY Feeling the Heat

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    So I've been burning pellets for over a year now in my Fahrenheit Endurance 50 furnace (sorry, haven't posted in here in awhile, been real busy), and over that year I wanted to share an observation of mine that may be redundant information that most everyone already knows (I apologize if this is the case). I searched the forum a few times and couldn't find too many topics dedicated to wood pellet length (other than long pellets causing augers to jam up), so I thought I'd post my own thoughts on the subject here and find out what others think about the conclusions that I am drawing here on pellet size (length)...

    By "short" length pellets, I'm referring to bags that contain pellets that are on average shorter than 1" long (avg. seems to be 1/2"). Long pellets generally consist of pellets that avg. 1" or longer in length in a bag/batch.

    * Longer pellets produce less heat than shorter pellets - I'm no combustion expert, but the reason for this likely relates to surface area and how the auger moves pellets to the burn pot. Smaller pellets provide more surface area exposed for burning, therefore they seem to burn with more intensity than longer pellets, hence producing more heat in a shorter time span.

    * Longer pellets feed more slowly than shorter pellets - at the same burn level (my furnace has levels 1-5, with the "levels" generally referring to lbs/hr burned), longer pellets seem to feed more slowly than shorter length pellets. It seems that I'm refilling the hopper more frequently when my hopper is loaded with short-length pellets. This is another reason why shorter pellets likely produce more heat than longer pellets, they are feeding more quickly at the same burn level (more slip into the burn pot when the auger turns). One thing remains consistent however, longer pellets result in a cooler burn.

    * Longer pellets produce different ash characteristics - ash from short-length pellets (at least in my Fahrenheit unit) is almost as white as snow. Longer-length pellets produce darker colored ash. However, ash characteristics still vary widely based on pellet manufacturer and batch. I've had hot-burning batches produce darker ash while cooler burning batches produce a gray/white ash.

    Now, this may just be a characteristic (aka feature) of my particular Fahrenheit furnace, but I definitely seek out wood pellets that are shorter in length as they consistently seem to produce more heat than pellets that avg. 1" or larger in size in a bag or batch, but at the cost of more being consumed per hour to achieve that additional heat output. In fact, I've found that longer length pellets produce roughly the same amount of heat on level 4 that short length pellets produce at level 2. If I crank my furnace to Level 4 while burning shorter-length pellets, my entire 2500 sq. ft. home roasts (downstairs climbs to 78°F+). My observations of pellet length spans at least 6 or 7 differing pellet brands (AWF, Wood Fibers Inc., Fireside Ultra, Stove Chow, Lignetics, Pennington, just to name some that I've burned, at least 10-15 bags or more).

    It may seem that the hotter burn characteristics of shorter pellets boils down to shorter pellets seemingly feeding at a faster rate. However, on really cold days, I've noticed that my furnace produces much more heat when burning "short" pellets at a lower burn level, allowing me to lower that burn rate, ultimately using less pellets in a day than I would use burning longer-length pellets at twice the feed rate. I also thought I read somewhere that pellet grades (i.e. premium , etc.) are supposed to include length specification. Perhaps this observation of mine is old news...

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  2. tjnamtiw

    tjnamtiw Minister of Fire

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    You've observed one of the most overlooked variables in running a pellet stove. So many people here think that a pellet is a pellet is a pellet. They fail to realize how pellet length affects the burn and heat output of their stove. They will look at a hundred other things to blame when, in fact, the first thing they should do is adjust their stove to suit the pellet they are burning. With Quads and others, it is the flame height on HIGH heat setting.
    I think that shorter pellets allow more mass to be conveyed while long pellets hog space in the auger and can't be packed as densely. This then requires an increase in feed rate be it opening the feed adjusting plate or whatever means is available for your stove.
    Don't know about the color of the ash being related to pellet length though. I would think it has more to do with what the pellet is made of.
  3. ChrisWNY

    ChrisWNY Feeling the Heat

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    Agree 100%, tj. I think a lot of woes would be solved if people adjusted feed rates on their stoves based on the avg. length of pellets they are burning. If you're dealing with long-length pellets, crank that feed rate up a notch or two and heat output improves while overall consumption likely stays nearly the same as it did when burning shorter pellets at a lower feed rate. You're probably right about ash color, it's probably related to the composition of the pellet itself, and which woods were used. Pellets producing light gray/white ash however seem to burn a little hotter (generally speaking) than pellets that produce a darker colored ash, but that's not always the case in my past experience.
  4. aaronnoel

    aaronnoel Member

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    Agree as well, short pellets burn the hottest, my North American pellets are very short and burn real hot, I have found that they also burn faster and I wonder if that a product of real shot pellets as well. Most of N.A's pellets are under 1/2 inch in length.
  5. HD41

    HD41 Member

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  6. jtakeman

    jtakeman Minister of Fire

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    The fella down at the boxstore told me all these here pellets are the same and even bagged at the same place even. Gollie gee who'da thunk we see a difference in them there wood pellet thingies?

    Wonder iffin the bulk density matters?

    :cheese: running for cover! :lol :cheese:
  7. SmokeyTheBear

    SmokeyTheBear Minister of Fire

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    Anyone out there still think that pellet stoves feed by weight?
  8. jtakeman

    jtakeman Minister of Fire

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    Well heck ya! Says so right in that there manual thingie I be reading. Also say I musta clean this here stove. Why'd ya need to do that? :gulp:
  9. Czech

    Czech Minister of Fire

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    I use that ignorance to my benefit. The guys in the yard don't know the difference between the more expensive and better softwoods from the junk lot of ash whatever pellets. I know what I have them load in my truck!
  10. jtakeman

    jtakeman Minister of Fire

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    Did you ever hear this one?

    ;-)
  11. pete324rocket

    pete324rocket Feeling the Heat

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    Thank you for addressing this topic and putting your conclusions all together in one post.
    My observations: My longtime source for pellets started chopping their pellets about half of what the length used to be and it was mentioned to me by the delivery man and the information just blew by me. I now find that the stove is consuming a bag of pellets faster than any brand ever before. I also notice a rise in temperature at the lowest setting. My only conclusion in my mind is that more pellets are being fed thru the auger (because they are choped finer) and as a result is the rise in temperature. The pellet bags also seem "less full" even though the weight is the same , so it seems more compressed pellet material is occupying a smaller volume, and that is not to hard to comprehend. For the dealer, it could "appear" that the pellets have more heat and are "hotter", and I can't say I 'd blame any manufacturer for being smart like that(to encourage brand favoritism) but I'd have to say that I bet not very many people are aware of it.
  12. jtakeman

    jtakeman Minister of Fire

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    If your stove has a thermostat? It will only run until the temp satifies the stat. Its the pellet size/density equalizer. Or save them pupies for the cold season and find some longer/less dense stuff for the shoulders. Look for puffy full looking bags while pellet hunting! Skinny bags are the first key while looking for the stuff that should crank some decent heat! You'll also get more of the skinny bags into the hopper.

    Some of the newer stoves have feed trim adjustments to compensate. Quad has a fuel gate in the hopper which works to reduce feed of the fuel to the pot. Think there are a copuple more, But I have CRS bad on Mondays!
  13. gymrat0663

    gymrat0663 Member

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    Great info for us newbies!

    Thanks for posting this!
  14. Snowy Rivers

    Snowy Rivers Minister of Fire

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    Let me add this little tid bit that confirms your theory.

    I burn hazelnut shells in my two whitfields.

    This stuff is more granular in consistency, with the largest pieces about the size of your little fingernail and the smallest pieces maybe 1/8th inch chips.

    The auger feeds this stuff at a far different amount than it would pellets.
    The average delivery per auger cycle is probably a teaspoon full each cycle.

    I rarely run the stoves past the number one setting.

    The BTU per pound is similar to most premium wood pellets.

    The heat output is far higher than the same setting using most pellets.

    Reason being, the material can burn faster and hotter than the larger pieces.

    Think of it as comparing a "Kindling fire" to a large log slowy glowing away and the firebox.

    Just some thoughts.

    snowy
  15. ChrisWNY

    ChrisWNY Feeling the Heat

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    Thanks, glad this post is of some value to new pellet burners. I know I didn't realize pellet length was a factor when I first had my Fahrenheit pellet furnace installed over a year ago. During that time I was busy trying out different pellets from different manufacturers to find out which burned best/hottest/cleanest, and there are plenty of threads on this forum that compare pellet brands that help others to decide on which brand to buy. What I found was that out of the various pellets I bought last year, the ones that burned the hottest were the shortest. My furnace seems to have a high burn efficiency, no matter what type of pellet I feed it, it burns with very little ash left behind.

    I can go 2-3 weeks burning at least a bag a day without dumping out my ash pan (the Fahrenheit's ash pan is huge but it's still amazing how little ash is produced from an entire 40 lb. bag of pellets. I'd estimate less than 4 oz. of ash per bag on avg). It didn't make too much difference of what brand of pellets I bought, they all seemed to produce about the same amount of ash, the only big difference I noticed was the heat output when burning shorter pellets. I've noticed some pellet manufacturers seem to be "dicing" up their pellets more so than they did a year ago. This year I bought 1 ton of AWF pellets before the season started (mid Fall), the pellets were medium length, on average 1/2-1" long. Just yesterday I bought 15 bags of AWF, the pellets were all diced up, very few being longer than 1/4". Dumped a bag in there yesterday, they're burning hotter than hell. Pellets seem to be exact same color and of the same materials of the older (last year's) batches, length seems to make all the difference.
  16. tjnamtiw

    tjnamtiw Minister of Fire

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    That was my point. If they feed faster, you are putting more lbs/hour into your stove and therefore getting more heat. It's a simple law of physics. That's again why you must adjust your stove to get the correct feed rate (lbs/hour) as prescribed for your stove. If you don't do that, you stand the chance of overfiring your stove, which could result in warping, cracking, or otherwise destroying your stove.
  17. tjnamtiw

    tjnamtiw Minister of Fire

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    From reading many of the posts and seeing some of the pictures of warped, cracked stoves, yes I do, Smokey. :p
  18. IHATEPROPANE

    IHATEPROPANE Minister of Fire

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    Yup right on about the t-stat...I learned about the feed being about pellet size and density soon after I got my stove.....I was experimenting with a bunch of brands and the temp was within the ball park for all of them on the infrared. I then got to Currans blend....they were coming up 50 degrees hotter....I couldn't believe it.....then I noticed the bag lasted half as long....disappointed indeed....this year got the stat to even things out
  19. HD41

    HD41 Member

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    Early on I did heat output temperature comparisons on several single bags of different pellets (including an unnamed frequently bashed brand) and found significant differences in heat output on the same setting. I noticed size and feed differences but left the more detailed analysis to other members.

    I have settled on Somerset and Lignetics that perform well and have always been available and reasonably priced. I had to lower my feed rates to compensate. The only other pellets I burned in quantity were AMF American Wood Fibers, they produced less heat but this may have been because of size. Never had an auger jam or burning problems.

    Pellet reviews are helpful but are often mixed, If some brag, some bash and others say the same pellets are shoulder season they are probably ok if the price is right. I might want to try a single bag in my stove first.
  20. Easternshore Bob

    Easternshore Bob Member

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    My Mini loves short pellets!!!!!
  21. ironpony

    ironpony Minister of Fire

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    And remember boys and girls if you had a HarmAn stove
    none of this would matter
    as HarmAns are regulated by exhaust gas temp
    so ALL pellets put out the same heat


    runs and hides under pellet stash
  22. jtakeman

    jtakeman Minister of Fire

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    Maybe thats why they say their all the same? They musta been usin a Harmon(I know its spelled Harman-just bustin ironpony)! ;-)
  23. ironpony

    ironpony Minister of Fire

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    you good sir, have now opened the flood gates of spelling correctors

    let the posting begin
  24. jtakeman

    jtakeman Minister of Fire

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    ~~~~~~~~~~~~~IronPony~~~~~~~~~~~~~
    ^^^^^^^^^^^Back at this fella^^^^^^^^^^

    %-P ;-P :p :coolgrin:
  25. tjnamtiw

    tjnamtiw Minister of Fire

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    Why would you be disappointed about a bag lasting half as long when you were getting twice as many btu's per hour? :)

    Also, yes the thermostat turns the stove off or down but if you are over-firing when it's running,........................... OMG, enough is enough. Hot pellets, cold pellets, shoulder season pellets!!!!!!!!!!!!!!!!!!! Grrrrrrrrrrrrrrrrr. :zip: :snake:

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