Most Efficient Flame Level

[BitTwiddler]

At what flame level is a pellet stove (I have a Harman Absolute43) most fuel efficient? I am guessing that continuous at just enough feed to keep the room warm, for these reasons:
1. I don't get as much visible smoke at a lower burn, so less fuel escapes without being burned.
2. The exhaust temperature is lower, so less heat is just dumped outside.
3. Compared to "room sense" mode, the combustion fan doesn't run when there is no or low fire so the fan is not just dumping warm air up the exhaust vent.

Also, how much more efficient is the system when the room fan is higher? I know that it *is* more efficient, but I don't know if it's enough to justify the noise it make - having numbers would help figure the best compromise point.

BTW I asked this through the Contact Us link on Harman's web site, but they just referred me to my deal, who has no hard data and apparently cannot get it from Harman, either.

 

[Connecticut Yankee]

That's a great question. I have limited experience with pellet stoves, but I can tell you that the desired inside temperature, the outside temperature, and the rate at which the house loses heat are part of the equation. I am also told that each brand of pellets has different heat characteristics, and there is also a certain inevitable degree of variation between bags of the same brand.

Then there is the question of whether it's more costly to keep the fire going continuously, which requires a certain minimum feed rate, regardless of conditions inside and outside; or to let it go out periodically, which means figuring in the cost of reheating the stove to operating temperature from time to time throughout the day.

The stove's programming also matters. For instance, unlike your Harman's, my stove's combustion fan is always on, if the stove is running; the convection fan is also always on, but its speed varies with the temperature in the room. So far, except for a couple of really cold days, the lowest heat level has been enough to keep the family room close to 80°, but I have noticed that when we bumped up the heat level, the fan speeds also increased. So would it be necessary to know the actual RPM's, or do you think a feel for the relative changes in speed would be enough?

 

[BitTwiddler]

Thanks for the reply. The various temperatures you mentioned are all summed up in " just enough feed to keep the room warm", whatever total heat output that requires. At times that will require more than the minimum flame, and at others minimum flame will be too much.

As to room fan speed, I would think that the question is more like, "Will twice the fan speed extract X times the heat from the same sized fire, or only 10% more?" The converse question would be, "How much faster does the fan have to run to get X times more heat from the same size fire?" X might be 1.3 or 2 or whatever. I know that if I go from 10% fan to 100% fan and only get 30% more heat (X=1.3) I'll probably only run 100% fanwhen I'm not home but if I get 200% more (X=3.0) I'll be running at 100% fan quite a bit of the time and live with ringing ears.

 

[Tonyray]

Pretty sure my Harman exhaust stays on till last ember is gone and beyound.

 

[Ssyko]

 

[Golfeur]

In my case I have a house 3 floors and the stove is in the basement. I put the fan speed to the minimum so that the air comes out warmer and when there is a heat demand in the house the fan speed increases alone but does not increase to the maximum so the air still comes out very hot.
the air being hotter has more easily gravity mounted to the first floor and the second floor.
This is the first year that I'm experimenting with this way of heating and it seems better for me and because the warm air is better on the other 2 floors the temperature in the basement is lower than usual.
I have not seen a change in pellet consumption

 

[rich2500]

Pretty sure my Harman exhaust stays on till last ember is gone and beyound.

Mine does also, only shuts off if the stove has cooled enough before it calls for heat again, now with just glowing embers in the pot the fan kicks way down to the point that ts almost silent but it's still running.