Starting my second season with an Oslo .I have a 26 foot exterior chimney . Using hardwood aged two and a half years this thing just eats wood. Lights really easy.I tried putting a baffle in my stovepipe and it only helps a little. It gets hot when wide open but the temp drops when i cut the air past halfway. Only get 3 to 4 hours out of a load. Disappointed in the lack of overnight burn.
I get more than that out of my much smaller F3 (~1.1cu feet I think, compared with ~2.8cu feet for the F500) with hard woods. With soft woods, I can get 5 hours of heat often if loaded up to the max and I have a 28 foot chimney (interior though). Now if you're talking big flames, I can get 1.5-2hours out of soft wood, but it'll be rocking away at 350-400 degrees 3 hours in even with soft wood.
Jotul does also say in the manual that if your wood is TOO seasoned, you won't get significant efficiency improvement through using the stove. Although I don't think anyone but Poindexter has ever had that problem in reading the forums
. Therefore I REALLY doubt that's the issue.
Here is the money quote:
page 14 of the F3CB manual
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The F 3 CB is designed to burn natural wood only. Higher efficiencies and lower emissions generally result when burning air-dried, seasoned hardwoods, as opposed to softwoods, green or freshly cut hardwoods. Wood that has been air-dried for a period of 6 to 14 months will provide the cleanest, most efficient heat. Wood seasoned more than 2 years will burn too quickly to take advantage of the stove’s low end efficiency strength.
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Some questions that come to mind as I read through this:
What's the wood moisture content? (freshly split, middle of the piece)
Any block off plate or insulation? (you said it's an exterior chimney.)
What temps are you getting? (wherever you're supposed to measure it by the manual)
Dollar bill test negative?