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...
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...
!!
