Another secondary burn question

[leoibb]

hello all , i have my stove burning from the top only , or should i say secondaries only no flames from the wood or not really and red coals, is this good or bad? i was told that the secondaries give more heat hence the reason behind it. i dont have any tubes in feeding air just a vermiculite baffle i created my self instead of the steel one, secondaries seem to work fine but them alone how efficient is it to do it? , i can post links for vids

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[etiger2007]

Do you have smoke coming from chimney while you are burning wood?

 

[WellSeasoned]

That's exactly what secondaries look like. That is burning the gases and is perfectly normal. This is efficient, and why we burn 1/3 less wood.

 

[Corey]

Burning with 'only' secondary combustion is burning 'right on the edge' IMHO. You wood is giving of gas/smoke, but it is not hot enough to burn right at the wood. Once this gas gets to the top of the stove, in the heat, it can then catch fire and burn...the radiant heat from that burn helps vaporize a bit more gas/smoke from the wood and the process continues. It is somewhat like burning a candle in a breeze where you see the flame is detached from the wick by some small distance, but that is a very unstable way to burn as the flame could easily blow out. In your video, it actually looks like that happens around 2:06, then about 2:17 there is a flashover the the flames re-ignite.

Basically when you have flames like that, you're balanced on a knife edge and one of two things will happen. Either you are ahead of the 'thermal curve' and the heat from the secondaries will ignite the wood below and cause flames from the wood to flare up into the secondary combustion zone. Or you are behind the thermal curve and the secondaries go out leaving a smoldering pile of wood in the bottom.

As far as 'more heat' with secondaries that is a bit subjective. Given two identical burns with some smoke going up the flue, add secondary combustion to one, then yes you are getting more heat as you are burning smoke which would otherwise be lost. But do secondary flames alone put out more heat than a fully fired stove with wood, coals and secondaries blazing...most likely not.

 

[leoibb]

thankyou for the imput , ive always found it facinating to get the secondaries burning without the bottom , wasnt sure how efficient it was, but post above is correct i cant keep them going like that for too long .

 

[corey21]

Burning with 'only' secondary combustion is burning 'right on the edge' IMHO. You wood is giving of gas/smoke, but it is not hot enough to burn right at the wood. Once this gas gets to the top of the stove, in the heat, it can then catch fire and burn...the radiant heat from that burn helps vaporize a bit more gas/smoke from the wood and the process continues. It is somewhat like burning a candle in a breeze where you see the flame is detached from the wick by some small distance, but that is a very unstable way to burn as the flame could easily blow out. In your video, it actually looks like that happens around 2:06, then about 2:17 there is a flashover the the flames re-ignite.

Basically when you have flames like that, you're balanced on a knife edge and one of two things will happen. Either you are ahead of the 'thermal curve' and the heat from the secondaries will ignite the wood below and cause flames from the wood to flare up into the secondary combustion zone. Or you are behind the thermal curve and the secondaries go out leaving a smoldering pile of wood in the bottom.

As far as 'more heat' with secondaries that is a bit subjective. Given two identical burns with some smoke going up the flue, add secondary combustion to one, then yes you are getting more heat as you are burning smoke which would otherwise be lost. But do secondary flames alone put out more heat than a fully fired stove with wood, coals and secondaries blazing...most likely not.

+1 i also think that burning like that eat the wood faster then combination fire.

 

[WidowMaker]

Not sure about it eating more wood, but I have found that I cannot sustain the the stove temps needed to heat the house or the internal temp needed to to sustain that burn for continous burn and then itstars to smoke. My stove wants a little primary air to maintain goog burn ad good heat output. That said, a little more chimmney height, more draft, might help my sisutation, I only have about 12ft...

 

[leoibb]

as it happens ive always burned from the top air only however i notice that when open full or nearly full the air blows down the glass fierce and almost blows the flames off the wood, so ive done it different for last day or two, i did open the bottms ever so slightly and lowered the top opener, and the stove feels much hotter and a nice box full of flames not fierce just little bit more than steady away.

 

[begreen]

as it happens ive always burned from the top air only however i notice that when open full or nearly full the air blows down the glass fierce and almost blows the flames off the wood, so ive done it different for last day or two, i did open the bottms ever so slightly and lowered the top opener, and the stove feels much hotter and a nice box full of flames not fierce just little bit more than steady away.

Sounds like you are getting the hang of it. For most of us the goal is to maximize efficiency and heat output. A big flaming light show is pretty, but often less efficient.

When you get a chance can you add your stove make/model to your signature? That is helpful info.

 

[leoibb]

hi thanks for that. it is a titan i believe to be china stove, i have done some very slight mods to it. i wasn't happy with the lining or baffle so i lined it and made new baffle with vermiculite board. i am going to get the burley wakerley stove, ive paid a deposit on it, but since cleaning the flue liner and sealing it this stove is different again as in much better, next job is get a stove thermometer. what temps should the top and pipe be for maximum efficiency

 

[begreen]

Stove top temperatures vary with the fuel and the stove. Ideally you want the flue temps to be below the stove top temps, but not so cool as to promote creosote accumulation. A rough target might be 5-600 on the stove top and 3-400 on the stove top if you can get a direct reading off of it.

 

[Wood Duck]

I think secondaries only is an efficicent way to burn, but like Corey said it is hard to maintain. I try to have enough air that I get a little flame down at wood level. This helps keep the secondaries going steady without flashing on and off.

 

[Corey]

It is a bit hard to tell from the video, but the most 'efficient' burn will happen when you have translucent blue / purple flames in the stove. This is a sign you are burning carbon all the way through CO and into CO2. If you see the typical red / orange / yellow 'candle flame' type flames, this results from glowing carbon soot in the flame and is overall a less efficient burn because there is energy left to recover in the carbon. It's like sending a fine trail of coal up the flue!

So even though you have 'secondary burn' it's only hitting maximum efficiency when the flames become transparent. Sooty/yellow secondary flames help, but still not getting max efficiency.