Top down burning?

[amateur cutter]

Okay, I'm sure this topic has been discussed here before, but the search didn't find the answer. Basically, how to in a wood furnace. I've heard it's very efficient & makes the fire burn longer. I've got a older longwood furnace with a 4' deep firebox. Would appreciate instructions, opinions, experiences, etc. Thanks much. A C

 

[soupy1957]

You state a "wood furnace" and I'm gonna ask for clarification. If you are talking about a wood burning unit that sits outside, it has dynamics to it that are somewhat different than an indoor wood stove.

Just talking about the way to BUILD a fire, another topic, I've done both, and it's totally arbitrary. I may "top down" on some occasions and may do it differently on other occasions. There is no set rule really..........it's just about what you feel comfortable with, and what works best in your system, by trial and error.

-Soupy1957

 

[amateur cutter]

Indoor wood furnace, long round firebox. The furnace is in my shop if that matters. I'd heard of people getting longer burn times with the topdown burn, which would be really nice. A C

 

[vvvv]

yes top down by whatever means. bottom up burn results in an accelerational fire where the load gets heated & may not have enough combustion air as it gets hotter & offgases faster

 

[LLigetfa]

I must be missing something. Top-down is just a way to start a fire. Once the fire is going, it becomes a bottom-up fire from then on.

I can't see shovelling out all the coals, putting wood in, and then putting the coals on top of it.

What I often do is a front-back fire. I pull all the coals to the front and put the wood behind it.

 

[cityhick]

You can find the top down fire method at woodheat.org

 

[oldspark]

Just when you think you have seen it all..........

 

[firefighterjake]

I'm surprised a search didn't bring up any info on top down fires . . . especially since I just had a thread that contained info on the top down method of starting a fire.

Here's the basics . . . the top down method of starting a fire is simply one method of starting a fire . . . and starting a fire in a wood furnace, woodstove, fireplace or fire pit is pretty much the same regardless of what is holding in the fire.

The top down method is not really efficient in terms of creating a fire that burns longer or burns hotter, but it does have some perks compared to other methods of fire starting -- namely it establishes a draft early on, it burns from the top down so that unlike the "teepee" or "log cabin" method you don't tend to have wood that collapses on itself causing the fire to smolder or suffocate and the really nice aspect is that once lit the fire pretty much burns with a large load of wood until you are ready to reload the firebox -- there's no opening the door to stick on another piece or two of wood.

How to . . . put 2-3 splits on the base, leaving some room between them. On top of this place 2-3 smaller splits. On top of this place kindling or firestarter of your choice. Light kindling/fire starter, keeping air control open (you may also need to keep the door open slightly depending on your set up). Once the fire gets going shut the door . . . and when it really gets going start closing down the air until you achieve the perfect balance of good heat, good burning and good temps in the stove/flue.

 

[Mushroom Man]

Does this method work in a downdraft gasifier? I tried it once but failed. I am certainly willing to admit that my wood wasn't the driest and that may have been a reason for the failure.

It would be great to avoid the collapsing and smoldering issues in favor of a sure start.

 

[firefighterjake]

Does this method work in a downdraft gasifier? I tried it once but failed. I am certainly willing to admit that my wood wasn't the driest and that may have been a reason for the failure.

It would be great to avoid the collapsing and smoldering issues in favor of a sure start.

Not really sure . . . never having burned in one of these . . . perhaps some other folks who may have had experience will chime in . . . it seems to me that starting the fire in any of these stoves is about the same . . . the difference occurs when the air is cut back and the real "magic" begins by using downdraft tech, secondary burns or cats.

 

[vvvv]

I must be missing something. Top-down is just a way to start a fire. Once the fire is going, it becomes a bottom-up fire from then on.

I can't see shovelling out all the coals, putting wood in, and then putting the coals on top of it.

What I often do is a front-back fire. I pull all the coals to the front and put the wood behind it.

yup missing a lot, foremost that this is not an epa burner otherwize= a load of wood on a bed of coals results in the bottom of the wood offgassing & burning first. as it gets hotter, the wood above heats up & also offgases which results in accelerated fire that wants more combustion air to burn fully.
ma nature sez= colder air rushes to the hotspot so to displace the hotter air emanating from the hotspot & this is called air BUOYANCY. this also explains how an EPA stove can bring in primary air from the top of the firebox next to the firebox outlet & it still feeds the fire instead of going directly up the closer & drafting flue!
coals to the front is the practical way no doubt

 

[oldspark]

I must be missing something. Top-down is just a way to start a fire. Once the fire is going, it becomes a bottom-up fire from then on.

I can't see shovelling out all the coals, putting wood in, and then putting the coals on top of it.

What I often do is a front-back fire. I pull all the coals to the front and put the wood behind it.

yup missing a lot, foremost that this is not an epa burner otherwize= a load of wood on a bed of coals results in the bottom of the wood offgassing & burning first. as it gets hotter, the wood above heats up & also offgases which results in accelerated fire that wants more combustion air to burn fully.
ma nature sez= colder air rushes to the hotspot so to displace the hotter air emanating from the hotspot & this is called air BUOYANCY. this also explains how an EPA stove can bring in primary air from the top of the firebox next to the firebox outlet & it still feeds the fire instead of going directly up the closer & drafting flue!
coals to the front is the practical way no doubt

OK, how do yu do a top down fire if not just to start it, in layman's terms please not blimp talk!

 

[Skier76]

Top down is really only for starting. When the stove is warm and there are coals, I throw kindling up front, and bigger splits in the rear...then cross a medium split over the top.

I had only marginal success with the top down in our Jotul. I think it was mostly due to firebox size. That baffle plate made it tough to do a true top down. I'd build the fire like a top down, but stick birchbark somewhere under the small kindling to get that going.

 

[vvvv]

I must be missing something. Top-down is just a way to start a fire. Once the fire is going, it becomes a bottom-up fire from then on.

I can't see shovelling out all the coals, putting wood in, and then putting the coals on top of it.

What I often do is a front-back fire. I pull all the coals to the front and put the wood behind it.

yup missing a lot, foremost that this is not an epa burner otherwize= a load of wood on a bed of coals results in the bottom of the wood offgassing & burning first. as it gets hotter, the wood above heats up & also offgases which results in accelerated fire that wants more combustion air to burn fully.
ma nature sez= colder air rushes to the hotspot so to displace the hotter air emanating from the hotspot & this is called air BUOYANCY. this also explains how an EPA stove can bring in primary air from the top of the firebox next to the firebox outlet & it still feeds the fire instead of going directly up the closer & drafting flue!
coals to the front is the practical way no doubt

OK, how do yu do a top down fire if not just to start it, in layman's terms please not blimp talk!

you cant so pulling coals to front is next best thing

 

[oldspark]

So LLigetfa was not missing a lot?

 

[vvvv]

So LLigetfa was not missing a lot?

just the general understanding of how fire & stoves work, which i tried to explain somewhat

 

[oldspark]

So LLigetfa was not missing a lot?

just the general understanding of how fire & stoves work

Is that all? :cheese:

 

[LLigetfa]

...which i tried to explain somewhat

Is that what you call it? I guess you will have to explain your explanation.

 

[Jags]

To the OP - FFJ pretty much hit the ball out of the park. Will it make a fire last longer?? Probably not noticeable if at all. Well, it could, but it would have to sacrifice btu creation in some way (meaning that if the fire lasts longer, it does not burn as hot). The btu content in a pound of wood is pretty consistant.

The real advantage of a top down is with EPA stoves. The fire will start to immediately heat the re-burner (tubes or cat). It doesn't have to travel through the wood pile.

I have tried every way from Sunday, and I always revert back to my boyscout days. Tinder, kindling, wood, except now I replace the tinder and kindling with a fire starter and a stick lighter. POOF - 10 min - big flame. Ugg, ugg, fire good.

 

[fossil]

Yup..."top down" refers only to a method of starting a fire from cold. It's not a "method of burning"...just an alternate way to get a fire going. After the fire is going, "top down" has no meaning as to how the burn progresses, or how the hot reloads are done. Rick

 

[vvvv]

Yup..."top down" refers only to a method of starting a fire from cold. It's not a "method of burning"...just an alternate way to get a fire going. After the fire is going, "top down" has no meaning as to how the burn progresses, or how the hot reloads are done. Rick

now consider the functioning of a downdrafting gassifying boiler

 

[Delta-T]

Yup..."top down" refers only to a method of starting a fire from cold. It's not a "method of burning"...just an alternate way to get a fire going. After the fire is going, "top down" has no meaning as to how the burn progresses, or how the hot reloads are done. Rick

now consider the functioning of a downdrafting gassifying boiler

I'm not "in the know" about gasification boilers, so, cut me some slack on this, but isn't the downdraft a function to increase residency time in the combustion system? You still need the bed of coals under the fuel to cause the outgassing, and then the down draft forces the gasses back through the coals to increase the combustion temps to over 1000 in order to get the VOCs to combust, no? In theory, i think if you could create and sustain a fire where the coals rested atop the fuel you wouldn't get the kind of combustion that would be desirable.

Of course, I could be very very wrong.

 

[vvvv]

Yup..."top down" refers only to a method of starting a fire from cold. It's not a "method of burning"...just an alternate way to get a fire going. After the fire is going, "top down" has no meaning as to how the burn progresses, or how the hot reloads are done. Rick

now consider the functioning of a downdrafting gassifying boiler

I'm not "in the know" about gasification boilers, so, cut me some slack on this, but isn't the downdraft a function to increase residency time in the combustion system? You still need the bed of coals under the fuel to cause the outgassing, and then the down draft forces the gasses back through the coals to increase the combustion temps to over 1000 in order to get the VOCs to combust, no? In theory, i think if you could create and sustain a fire where the coals rested atop the fuel you wouldn't get the kind of combustion that would be desirable.

Of course, I could be very very wrong.

boiler is equivalent to upside down stove= load in boiler is surrounded by water jacket which keeps the top of the load cooled, bottom of load sits on coals & burns. draft pulls the pyrogas down thru the coals & secondary air is thereafter brought in & this is highly efficient & smokeless. imagine the boiler upside down & its similar to EPA stove burning from the top down which is ideal but impractical , & thus the coals are raked to the front. if the EPA stove had a full bed of coals & a load of wood was put in, the bottom wood,sitting on the coals, would ignite first & the load would heat from the bottom up, accelerating its gassification & requiring more combustion air for stochiometric burn. this is true for non-EPA burner also....ithinx, but the EPA has the overhead tubes which create the fire on top or the hot zone

 

[Jags]

Yup..."top down" refers only to a method of starting a fire from cold. It's not a "method of burning"...just an alternate way to get a fire going. After the fire is going, "top down" has no meaning as to how the burn progresses, or how the hot reloads are done. Rick

now consider the functioning of a downdrafting gassifying boiler

I'm not "in the know" about gasification boilers, so, cut me some slack on this, but isn't the downdraft a function to increase residency time in the combustion system? You still need the bed of coals under the fuel to cause the outgassing, and then the down draft forces the gasses back through the coals to increase the combustion temps to over 1000 in order to get the VOCs to combust, no? In theory, i think if you could create and sustain a fire where the coals rested atop the fuel you wouldn't get the kind of combustion that would be desirable.

Of course, I could be very very wrong.

boiler is equivalent to upside down stove= load in boiler is surrounded by water jacket which keeps the top of the load cooled, bottom of load sits on coals & burns. draft pulls the pyrogas down thru the coals & secondary air is thereafter brought in & this is highly efficient & smokeless. imagine the boiler upside down & its similar to EPA stove burning from the top down which is ideal but impractical , & thus the coals are raked to the front. if the EPA stove had a full bed of coals & a load of wood was put in, the bottom wood,sitting on the coals, would ignite first & the load would heat from the bottom up, accelerating its gassification & requiring more combustion air for stochiometric burn. this is true for non-EPA burner also....ithinx, but the EPA has the overhead tubes which create the fire on top or the hot zone

Translation from Pookese:

It won't work as well in a downdraft gassifier. The smoke needs to be pulled through the hot coals.

 

[Delta-T]

hmmm, I am familiar with these principles. have you seen the "afterburner" (which i think they now call the Fire Dome) that Harman uses? Seems similar to this gasification boiler concept = no tubes, combustion air from the upper front of the stove body, drafting into lower back section, extra air added= clean burn. Had to say stochiometric didn't you? Now I gotta break out the dictionary. S...S....st.....sto....