Upside-down fires

[jaunty]

It seems that one can often get much more complete combustion of wood by laying a fire "upside-down" -- that is, by putting large pieces on the bottom, and progressively smaller wood on top.  The top of the firelay is lit, and, if the layers are sufficiently closely packed, coals can't fall to the bottom, so the fire burns its way down gradually. 

http://ca.youtube.com/watch?v=5SHBRVs1LQg

http://www.ozarkdreams.com/fires.htm

The advantage is that the volatiles that are cooked out of unburnt wood are drawn through the flames and ignited before they go up the chimney.  In fact, one might say that it's conventional fires that are really upside-down, because they send much of the fuel in the opposite direction from the hottest part of the flames. 

I'm wondering whether anyone has long experience with this kind of fire in a trail stove.  It might be a safe, clean  way of burning a relatively slow fire, and thereby keeping a tent heated moderately for an extended period.  (I'm interested in keeping the tent heated somewhat at night, if I can do so without taking undue risk or having to load the stove too often.  I do have a relatively large stove.) 

There are variations on the basic idea that, for example, use layers of ash to slow the progress of the fire from one layer to the next beneath it.  I can't see getting that fancy when camping. 

When this approach is used to burn wood chips, I understand that it can sometimes cause considerable heat stress in the firebox, as there can be a sharp temperature gradient at the level at which combustion takes place.  I would hope that that wouldn't be such a problem with larger pieces of fuel. 

But note that I'm not recommending this approach -- any experimentation is at your own risk.   

-- John T. 

[lost_patrol]

Don Kevilus of Four Dog Stoves recommends starting fires with the splits on top of the larger chunks.  Apparently it's the conventional method in Europe.  I've never tried it, but I presume the Europeans wouldn't do it if it didn't work.

[Georgi]

The 2nd link picture is typically how I start a fire, I didn't think that was considered upside down though....

[lost_patrol]

What's upside down about a propane torch?

I love the smell of napalm in the morning . . .

[jaunty]

Georgi -- I agree -- the second link may not provide the most helpful illustration of the method.  I just thought I'd include it as another reference to the technique. 


lost_patrol: Thanks for mentioning Don Kevilus' advice.  Apart from its potential for more complete combustion, putting the kindling on top may help to get the stovepipe warmed and drawing quickly. 


-- John

[jaunty]

I talked to Don Kevilus about this.  He calls it the Scandinavian method, but isn't keen on it.  As he says on his website, small wood is good, big wood is bad.  If you pack your wood in too tightly, it's as if it were in big pieces.  The disadvantage is that it won't get enough air and heat to turn it into proper fuel for the fire. 

To keep a fire going at night, he emphasizes the importance of starting with a good bed of coals, and raking the coals forward so that the new wood will benefit from their heat.  To ensure adequate air circulation, he'll criss-cross his wood slightly, 10-15 degrees one way, then 10-15 degrees the other, but apart from that he'll pack the stove fully.  He doesn't close the damper any more than halfway, so that he'll still get good combustion.  If the door leaks, making the fire hard to control, he uses some tin foil as a gasket. 

[jaunty]

Just thought I'd update this thread, as I happened to notice that since it was active a number of relevant videos have been posted on YouTube. 

Here's one of the shorter ones: 

http://www.youtube.com/watch?v=YLBBFU7Jg3k&feature=related

[Gapahuk]

Hi,

 ( I think there is a significant difference in an open fire and a fire in a stove.)

I always like to build a kind of upside-down fire in my tentstove.
I insulate  the  bottom of the stove with a layer of split logs. On top of these I lay two split logs to the left and to the right. ( All parallel to the length of the stove )
Than I lay small kindling across these two logs. On top of that, I fill the stove criss cross with some bigger kindling/small logs. I open the damper and light a candle and hold it in the  opening between the two logs and under the kindling. The kindling catches fire quickly, I take the candle out and shut the door immediately. At first I leave the air-intake open but because of the roaring fire I have to temper the airflow by reducing the  intake and closing the damper somewhat soon.

In this way the heat in the stove can build up quickly. The opening between the logs allows a good airflow. I don,t have to refill the stove for a while because of  the 'extra' logs from under the fire. In that way I don,t have to open the door (letting cold air in ), or have to ad cold wood, and the heat in the stove will maintain high. That,s important especially in the  beginning before there is a good hot coalbed.

Cheers,Ewout.

[lost_patrol]

Well, I've tried it again, and I've gone back to basics.  Tinder (birch bark, home-made fire-starters, crumpled sections of the Toronto Star or NOW magazine, whatever) on the bottom, small splits above that, then small junks of whatever you want to burn, bigger junks on top of that once the small stuff is going well.

It's not rocket science.  Heat rises, flames rise, fires burn from the bottom up.  And yes, don't pack the junks too close together.  Fires need oxygen as well as fuel.

And yes again, for cooking use small junks and feed the stove often so the fire is consistently hot.

Stay warm.

[chimpac]

A vertical stove is the best to burn upside down fires. The draft to the bottom has to be controlled or it turns into a melt down.
The old timers had the vertical potbelly stoves but they were not tight enough on the bottom for a slow contolled top down burn.
I have experimented quite a bit with top down burning and find I can usually burn steady, long, hot with little smoke. I pack in the biggest pieces I can get in then use some smaller stuff on top.
 My stove has a bottom grate and draft door that is shut to start the burn, the fire gets some bottom air from leakage and if its to much the fire burns to hot and to quick. To start with the fire needs fire starter and small stuff on top to get up to speed. You should always have flames at the top, if not the smoke from the bottom smothers your fire, and will do a smokey pooff when is does ignite again.
My slightly open feed door acts as the upper draft. The upper draft has to be directed at the top hot part of the fire.
 Check my posts to see my homemade stoves.