Prepacked burn: a strategy for older stove for maximum efficiency and indoor air quality
I have an old Fabco, a 1991 EPA stove that was before the age of secondary fire tube or cat. It’s able to have some secondary fire via the heated baffle.
I have been thinking efficiency and chimney cleaniness a lot. For the older non-cat, non-reburn stove like this, the most efficient mode of operation would be a roaring flame that would burn all the combustible gas and keep chimney clean as well. The optimal combusiton efficiency according to my EPA chart on the stove is with primary air half closed. Still enough air to fully burn everything, but not too fast to cause all the heat to leave the chimney.
This lead to my second thought. Normally, a cold start is inefficient. HOWEVER, in a stove that is intermittently operated, the thermal mass of the stove and its surrounding hearth can help absorbing additional thermal energy and re-radiate it to the house later, whereas in a continuous burning stove those heat would escape the chimney.
And then my third thought, which is the fact that while reloading is awesome for efficiency, it’s absolutely awful for indoor air quality due to flue gas coming into living space.
So with those thoughts in mind, I’ve been trialing this burn algorithm.
I think of my burns as prepackaged, with around 5-6 splits, using the top down method, with the largest splits at the bottom arranged north/south and arranged into a grid of squares. I aim for around 20lb of wood I think, around 200000 BTU.
I then use a very large amount of kindling (brown paper + small wood kindling) to create a very, very large, fast and hot burn off to one side. Think of it as the Ulam-Teller hydrogen bomb and the kindling is your primary which will ignite the secondary that is your main masses of wood.
The key is to have the fire going very hot as soon as possible, and top down fire heats up the flue and baffle fast (mine is metal) to allow optimal combustion and flue draw. I then gradually over around 3-5 mins shut down the primary air to 50%
The next part is important. Since owners of old stove like me cannot burn low and slow, we must extract as much thermal energy as possible while keeping flue temp above 500F at the stove top or so. I find the best way to do this is to turn the blowers to max and extract as much heat from the fire box as possible. This has the added benefit of preventing overfire.
With experience, you should be able to find the happy medium of your stove where you can achieve a 3-4 hour burn cycle with 1-1.5 hrs of flame time on even an old stove. I try not to reload with any flame left and instead just aim for one or two fires a day and use heatpump to supplement.
I hope this help you find the sweet spot of highish thermal efficiency, lowish chimney maintenance requirement and no reload which help with indoor air quality (my stove has an outside air supply)
![[Hearth.com] Prepacked burn: a strategy for older stove for maximum efficiency and indoor air quality](https://www.hearth.com/talk/attachments/trim-45f7ae2e-81f6-4f58-a041-29eab326f61e-gif.342986/ "[Hearth.com] Prepacked burn: a strategy for older stove for maximum efficiency and indoor air quality")
I have an old Fabco, a 1991 EPA stove that was before the age of secondary fire tube or cat. It’s able to have some secondary fire via the heated baffle.
I have been thinking efficiency and chimney cleaniness a lot. For the older non-cat, non-reburn stove like this, the most efficient mode of operation would be a roaring flame that would burn all the combustible gas and keep chimney clean as well. The optimal combusiton efficiency according to my EPA chart on the stove is with primary air half closed. Still enough air to fully burn everything, but not too fast to cause all the heat to leave the chimney.
This lead to my second thought. Normally, a cold start is inefficient. HOWEVER, in a stove that is intermittently operated, the thermal mass of the stove and its surrounding hearth can help absorbing additional thermal energy and re-radiate it to the house later, whereas in a continuous burning stove those heat would escape the chimney.
And then my third thought, which is the fact that while reloading is awesome for efficiency, it’s absolutely awful for indoor air quality due to flue gas coming into living space.
So with those thoughts in mind, I’ve been trialing this burn algorithm.
I think of my burns as prepackaged, with around 5-6 splits, using the top down method, with the largest splits at the bottom arranged north/south and arranged into a grid of squares. I aim for around 20lb of wood I think, around 200000 BTU.
I then use a very large amount of kindling (brown paper + small wood kindling) to create a very, very large, fast and hot burn off to one side. Think of it as the Ulam-Teller hydrogen bomb and the kindling is your primary which will ignite the secondary that is your main masses of wood.
The key is to have the fire going very hot as soon as possible, and top down fire heats up the flue and baffle fast (mine is metal) to allow optimal combustion and flue draw. I then gradually over around 3-5 mins shut down the primary air to 50%
The next part is important. Since owners of old stove like me cannot burn low and slow, we must extract as much thermal energy as possible while keeping flue temp above 500F at the stove top or so. I find the best way to do this is to turn the blowers to max and extract as much heat from the fire box as possible. This has the added benefit of preventing overfire.
With experience, you should be able to find the happy medium of your stove where you can achieve a 3-4 hour burn cycle with 1-1.5 hrs of flame time on even an old stove. I try not to reload with any flame left and instead just aim for one or two fires a day and use heatpump to supplement.
I hope this help you find the sweet spot of highish thermal efficiency, lowish chimney maintenance requirement and no reload which help with indoor air quality (my stove has an outside air supply)
