Does burning with 3-4" of ash in an insert effect the efficiency? When I burn with a lot of ash it takes longer to get the heat up, but the ash also seems to act as an insulater keeping heat longer. I could definitely clean ash out more often, but I don't like to do it when there are a lot of hot coals, so I try to wait until I can't burn for 10-12 hours.
I find that I get better heat transfer from my stove with less ash in the bottom. I believe that gives me better efficiency as I’m not having to run the stove quite as hard (more heat up the chimney) to heat the house... I often let my fire burn down overnight. After a week or so of burning, before getting a fire going again I will shovel ashes into a stainless pan and place in a metal trash can for later disposal... on occasion I will sort ashes from large hot coals prior to a reload and partially empty the stove...
So long as you leave at least 2" of ash in the stove you should be fine. But as for efficiency and the amount of heat, I've never noticed any decrease when the ashes get that deep.
Good question! I’m gonna lay low here myself and see what experiences have to say. I do tend to unload coals from my stove and they have been hot. Now to try and stop that and push the softwoods when I need to gain some space. Typically to just open the air and wait for them to cool down can be a long drawn out process so half my ash is unfinished charcoal. Still need to run it through a screen to get nails out.
The extra ashes might keep the coals from burning up since the air can't get to them. The coals seem to burn up faster if you stir them around and let them come to the top.
So I guess we can address the variables in the OP’s question. There is burning efficiency which I think would not be affected significantly by the amount of ash, except for the need to reload more often due to a infinitesimally smaller load being put in the stove each time. Then there is heat transfer efficiency which I believe is affected by increased amounts of ash, at least in my stove.. I have a blower and my stove is installed as an insert. So I get radiant heat from all sides of the stove, albeit less from the double walled portions on the back and top, as well as convective heat from the air pushed through by the blower. I have firebrick installed on the bottom, back and sides of my stove as well as a baffle in the top which I think provides sufficient insulation to prevent the stove from overheating or warping even if I start a fire with no ash in the stove. So in my opinion, the more ash I have in my stove, the less heat I see transferred via both radiation and convection due to the ash providing an extra ( and in my opinion undesired) insulation layer within the stove. Thus my heat transfer efficiency is less making my stove overall less efficient. Because of this, I will clean out the ashes prior to a cold snap and that seems to help.... one last thing that will affect efficiency is cleanliness of the air inlet and ducts for the blower. Just cleaned mine for the first time in 6months of burning..(last cleaning in Jan-Feb) This most recent cleaning was about 5 months overdue...
I notice that the coals burn down much faster right after the stove is shoveled out. In my stove anyway.
I report this also. The fire is slightly shorter lived towards the last half of it but really because it gains more air exposure below it rather than above
