Pellet feed rate vs heat output

[Manly]

I don’t believe I’ve seen this subject discussed in this context. If you increase the pellet feed rate, and the pellets burn well and completely, are you in fact increasing the btu output of the stove or just wasting pellets?

 

[johneh]

If you didn't get more BTU with more pellets they would make the stove non-adjustable
feed rate. One speed for all temperatures Btu are measured by (in this case ) pounds per hour

• Heat output: Pellet stoves can produce 8,000 to 90,000 BTUs of heat per hour.
• The lowest setting will burn about 1 ¼ lbs of pellets per hour, while the highest setting will burn about 5-6 lbs of pellets per hour.
• -------------------------------------- 8000 BTU ---------------------------------------------------------------------------90000 BTU
• You are only waisting pellets if you don't need the warmth

 

[Manly]

If you didn't get more BTU with more pellets they would make the stove non-adjustable
feed rate. One speed for all temperatures Btu are measured by (in this case ) pounds per hour

• Heat output: Pellet stoves can produce 8,000 to 90,000 BTUs of heat per hour.
• The lowest setting will burn about 1 ¼ lbs of pellets per hour, while the highest setting will burn about 5-6 lbs of pellets per hour.
• -------------------------------------- 8000 BTU ---------------------------------------------------------------------------90000 BTU
• You are only waisting pellets if you don't need the warmth

Thank you. That’s what I thought but manufacturers manual doesn’t address the issue directly, although they address flame limits. Pushing our little Francesca to the limit. Running like a deer last couple of seasons.

 

[bogieb]

It depends. If the stove has not yet reached the set point (assuming it has some sort of room temp sensing), then BTU's go up with more pellets (assuming complete burn in the pot).

If the stove has hit the set point, then a lot of stoves will throttle back the actual feed rate to match what it needs to keep the temp. Then if it needs more heat, will up the feed rate. In which case, the BTU's go up and down depending on what the stove is calling for. In this case, the feed rate is only what the stove is allowed to use if needed - but it has the option NOT to use that many pellets.

Or, depending on the stove and settings, it may throw excess heat out the exhaust. In which case, although technically producing more BTU, you do not get the benefit of those extra BTUs.

And of course, there are the boundaries of the stove itself as well as the pellets being used. I would think pot size combined with air flow would be a limiting factor on how many BTU's are actually producible by a stove (thus why a Harman P43 is rated at less BTUs than a P63). And, of course, the type of pellet being burned will also help determine BTUs possible.

 

[Manly]

It depends. If the stove has not yet reached the set point (assuming it has some sort of room temp sensing), then BTU's go up with more pellets (assuming complete burn in the pot).

If the stove has hit the set point, then a lot of stoves will throttle back the actual feed rate to match what it needs to keep the temp. Then if it needs more heat, will up the feed rate. In which case, the BTU's go up and down depending on what the stove is calling for. In this case, the feed rate is only what the stove is allowed to use if needed - but it has the option NOT to use that many pellets.

Or, depending on the stove and settings, it may throw excess heat out the exhaust. In which case, although technically producing more BTU, you do not get the benefit of those extra BTUs.

And of course, there are the boundaries of the stove itself as well as the pellets being used. I would think pot size combined with air flow would be a limiting factor on how many BTU's are actually producible by a stove (thus why a Harman P43 is rated at less BTUs than a P63). And, of course, the type of pellet being burned will also help determine BTUs possible.

Your comment on excess heat going out the exhaust is the concern prompting my original question. Makes sense that the physical size of the stove’s heat exchanger system is a limiting factor along with all the programmed settings. I don’t think I am squeezing extra heat out of my little Francesca by bumping up the feed rate. Undoubtedly the biggest influence on heat output for this stove is the pellets used. Thank you all for your input.

 

[johneh]

Now you are talking efficiency, not heat output
A pellet stove is rated at 75 to 90 % efficient
No matter how you burn it the efficiency remains the same
within that range. Yes the hotter the fire the more
heat lost out the exhaust that can be said for all heating appliances
Burn on a low feed rate on a day when the temp outside is -20
You most likely never get your home warm.