Burning Technique

[Heat Transfer Guy]

Here is some contradictory basic info I found online from reliable sources:

1) Generally, it is better to burn Less wood with MORE air to get the most out of your stove or fireplace. The wood is utilized in the best way when the air control is fully open and the flames are intense.

2) A fully open air control will lead to more heat being sent straight up the chimney rather than into the room (which reduces efficiency).

My background:
I'm using a Voyageur Grand insert with well seasoned wood. This is my second season using wood for heat. I understand what the desired secondary combustion flames at the top of the insert should look like. Although I'm in Southern California, sometimes we get a couple hours below freeing during the early morning hours. Oh yeah, almost forgot, I love my insert and it keeps my home really warm really cheaply!

My questions:

1) At times, we simply desire maximum heat output from our wood burner. We choose a large load of wood for this. The basic question is, more air for more flames or less air for less heat up the chimney? My guess is use maximum air, perhaps adjusted down just to prevent overheating the stove?

2) Other times we desire maximum efficiency from our wood fuel, i.e. the most heat output per split. For this are we setting air control as low as possible to just get minimal secondary burn flames? If the secondary flame sometimes goes out for a second or two is this ok, or is more air needed to raise efficiency?

3) Sometimes we need minimal heat output and maximum efficiency. Use more wood with less air, or less wood with more air? Too little wood might give too little heat, and prevent secondary combustion? Obviously less wood means opening insert more often to refuel.

My disclaimer:
Perhaps this has already been discussed to death on this forum. Instead of directing me to a further search, please be positive and provide a link to the previous discussion with your favorite answers if you don't want to add to the repetition. I understand there might not be definitive answers, and experience helps. Perhaps best rules of thumb can be provided for rookies? What to look for, what to avoid?

 

[firefighterjake]

Here is some contradictory basic info I found online from reliable sources:

1) Generally, it is better to burn Less wood with MORE air to get the most out of your stove or fireplace. The wood is utilized in the best way when the air control is fully open and the flames are intense. Mostly wrong . . . to start with the fire will typically need more air, but as the temp in the stove comes up you should reduce the air control to achieve the secondary, burn cleaner and send less heat up the chimney. With the air control all the way open, it may seem like you have an intense fire based on the view of the flames . . . and you do . . . kinda . . . but a good part of the heat is going up the chimney. If you shut down the air you would get an even more intense fire (i.e. Portal to Hell flames.)

2) A fully open air control will lead to more heat being sent straight up the chimney rather than into the room (which reduces efficiency). Mostly right.

My background:
I'm using a Voyageur Grand insert with well seasoned wood. This is my second season using wood for heat. I understand what the desired secondary combustion flames at the top of the insert should look like. Although I'm in Southern California, sometimes we get a couple hours below freeing during the early morning hours. Oh yeah, almost forgot, I love my insert and it keeps my home really warm really cheaply!

My questions:

1) At times, we simply desire maximum heat output from our wood burner. We choose a large load of wood for this. The basic question is, more air for more flames or less air for less heat up the chimney? My guess is use maximum air, perhaps adjusted down just to prevent overheating the stove? Start the fire with the air open . . . as the temp in the insert comes up start backing down the air control . . . depending on the installation and weather conditions you may be able to get to the quarter closed mark or more . . . at which point you will typically see the secondary flames and the heat will really start to pump out.

2) Other times we desire maximum efficiency from our wood fuel, i.e. the most heat output per split. For this are we setting air control as low as possible to just get minimal secondary burn flames? If the secondary flame sometimes goes out for a second or two is this ok, or is more air needed to raise efficiency? Same advice as above . . . me . . . I burn for maximum heat and maximum efficiency with the stove I have . . . hence I do the exact same thing every time. The only time I change things up a bit is during the shoulder season when I may not need a lot of heat . . . and in this case I moderate the heat output by the amount of wood I put in the woodstove, type of wood (I tend to go with wood that will burn hot and fast vs. coaling wood), etc. BrotherBart often says secondaries are not necessarily the end-all, be-all. Me . . . I like secondaries . . . but be aware that there are different types -- ghost flames, propane BBQ grill jets of flame, Bowels of Hell, fireworks, etc. I would suspect if you have bursts of secondaries you are OK, but you can also open up the air a touch to see if you get a sustained secondary.

3) Sometimes we need minimal heat output and maximum efficiency. Use more wood with less air, or less wood with more air? Too little wood might give too little heat, and prevent secondary combustion? Obviously less wood means opening insert more often to refuel. See above . . . a little trickier with a secondary burning stove . . . cat stoves do this very, very, very well. When I just need to take the chill out of the air I do one quick, hot fire (often with some chunks, softwood, etc.) and do not reload the stove . . . I let the stove heat up and then let the heat radiate off the stove.

My disclaimer:
Perhaps this has already been discussed to death on this forum. Instead of directing me to a further search, please be positive and provide a link to the previous discussion with your favorite answers if you don't want to add to the repetition. I understand there might not be definitive answers, and experience helps. Perhaps best rules of thumb can be provided for rookies? What to look for, what to avoid? Folks here are pretty friendly . . . we don't mind offering advice.

 

[Starstuff]

Everything that firefighterjake said is exactly what I do (and probably what most people around here do). I wonder if the advice you found regarding burning with air open is for burning in a non-epa stove (aka "smoke dragon"). That would make more sense, as more air would make it burn more efficiently and keep it from smoldering.

 

[jatoxico]

Sometimes we need minimal heat output and maximum efficiency. Use more wood with less air, or less wood with more air? Too little wood might give too little heat, and prevent secondary combustion? Obviously less wood means opening insert more often to refuel.

Jake covered it. I'll just add that when I need less heat I build a smaller fire that won't last too long. But you still have to burn hot to burn clean. To do that I use small, sometimes kindling sized wood and build the fire loose and airy. Air control tends to be a little more open since draft isn't always so strong in warmer weather.

Another option if you have it, is to use less dense wood like pine or poplar. These woods are sometimes called shoulder season woods around here because they can be used to make short but pretty intense fires.

 

[Heat Transfer Guy]

Firstly, thanks to all three of the above replies, I have gotten valuable information I was looking for from each. Sometimes nothing beats getting your own specific question answered instead of general instructions. Much appreciated. I am now on track with the idea of a hot fire burning for a shorter period on warmer days instead of my thinking of a cooler burning, too small fire.

...I wonder if the advice you found regarding burning with air open is for burning in a non-epa stove (aka "smoke dragon"). That would make more sense, as more air would make it burn more efficiently and keep it from smoldering.

When I started this thread, I took two sentences from two sources, then put them together because they both promoted more air. I do not think my picking out each sentence from context changed the intent of the original writer because they are both described as general tips.

The less wood, more air sentence came from an article dated 9/15:
https://www.hearth.com/talk/threads/tending-a-wood-fire-how-to-master-the-element-of-fire.147665/

The next sentence about control fully open for more air came from a book published in 2011. So no reason to think that info would be pre EPA stove era either:
(broken link removed to http://jotul.com/int/guides/eight-tips-for-burning-wood)

So now you can see why I described both sources as "reliable."

 

[Corey]

A modern stove is really like the carburetor on an engine, it needs 'just the right' amount of air at all times for best operation. More wood / less air can lead to a cool, smoky fire just like more fuel / less air leads to rich and smoky combustion in an engine. Too much air can cool the secondaries and put out those flames just like like it can lead to lean mis-fires in an engine.

Usually you will find the stove getting hotter and hotter as you CLOSE the air down, then at some point the temperature will start to drop as you close the air even more...that is the ideal point where you have 'just' enough air and max efficiency.