Saturday, March 5, 2016

Fire Layouts (Firing Up, part 2 of 3)



Rumford-style fireplace with V-fire
Basic skills are super-important for building self-reliant communities.  Managing fire is a basic skill, but it's not necessarily simple.

I told you in Part 1 that I'd use this post to say more about how to light a clean fire in any stove.
These tips are gathered from many sources, and confirmed by our personal experience: Ernie's time in the Midwest, Alaska, and North Pacific; Erica's physics degree and alpine-camping family, and of course our decade of working together on heaters, ovens, and fire science demonstrations.

Fire Laying Tips:
There are three common mistakes people make with fire.

"Grid" fire -
often used with
smoky, wet fuel

The #1 mistake is to use wet wood.
Don't do it.
As I said in the last post, it starves the fire of air, robs heat, worsens smoke and creosote problems, and is generally like trying to drive your car with both brakes on.
Think of your wood shed as kind of like a food dehydrator.
Get your wood in to dry about a year in advance.
The spring thaw, when your woodshed is at its lowest (NOW) is a great time to put up fuel for next year.

Second, don't forget fuel-air balance:
Many people think more air makes a cleaner fire. Sometimes it does, sometimes it doesn't. (Imagine lighting a match in a wind storm, for example.)  Every experienced fire-tender knows the spacing between the wood matters, and it's more a matter of instinct than measurement.
I'd guess that in an open fire, I usually leave ½ inch to 1 inch between pieces of wood, depending on their size.  Maybe half the thickness of each piece. With very small kindling sticks, or a rocket mass heater with its powerful draft, the sticks can just pack in as a bundle; the natural variations in shape allow in plenty of air.
Don't forget to close down the air slightly toward the end of the fire; even with no visible smoke, excess air cools the coals, and you get more carbon monoxide (CO) and less energy from the coals.

Third: Arrange the fire to suit its purpose.
If you only know one way to build a fire, it may not be the best option for every situation.  We use specific fires for light, cooking, or steady heat; to conserve wood, reduce smoke, or make tasty smoke for curing food; and to create specific impressions like security, elegance, or bravery. 
Let's look at the Grid, the Candle, the Tipi, the V-fire, and some specialized shapes for particular fireboxes like the Chimney/Rocket fire.




"Grid" fire - like Mom taught us
The Grid:
When I was growing up, we learned to make a sort of grid-stack, with kindling on the bottom (between a couple of bigger logs, if you don't have a grate). The biggest wood goes on top of the kindling, so the flames from the kindling will light the bigger wood (after warming it up and drying it out, if your wood pile is not well-sheltered). Using bigger logs to shelter the kindling is not a bad idea out in the wind, but the problem is that big wood on top: cold, unburned wood cools the flames, making smoke instead of fire. To see this without a fireplace, try sticking a spoon in a candle flame: it interrupts the clean burn, producing soot and smoke.
"Grid" fire -
with smoke escaping
from ends of logs

Cold big logs with a wimpy flame under the middle of them also tend to push steam and smoke out both ends, which doesn't catch easily when it's too far from the fire. The unburned smoke at the edges makes fellow campers miserable, or coats your chimney with creosote, instead of fueling the fire. 
  The fire will usually "catch" this way - and if it doesn't, it's easy enough to keep shoving newspaper underneath the whole pile until you dry it out enough to finally catch.  But it's never going to be a smokeless fire.


Smokeless fire is important for efficiency (as we discussed in Part 1), for safety, and for healthy air quality; and it's important for our final step in part 3 to safely store heat. 

Fox stove
(image from Art of Fire)
Before we cared about all these sensible goals, the most urgent motivator for smokeless fire was probably stealth.  Folks who run a smoky fire can be seen from miles away.

For thousands of year, humans have built specialized smokeless fireplaces, using simple tools like a shovel or stick, while discteetly passing through inter-tribal conflict zones.  A trace of smoke would lead your enemy right to your position.  Some of these stoves are underground, so that even the ashes can be hidden easily while breaking camp.  In civilized areas where we don't have to worry about raids by traditional enemies, our higher populations mean that we are subject to air stagnation warnings and burn bans.  You can make enemies by burning a noxious, smoky fire on the wrong day.  


"Candle" or "Upside-down" fire:
a cleaner starting grid fire,
recommended for box stoves
and masonry heaters
Candle Fire/ "Upside Down Fire":
For a less-smoky grid option, try a candle-style fire. The small kindling and paper at the top is the “wick,” and the bigger fuel below is the reserve, like candle wax.
Put your big logs on the bottom. Rack smaller logs above that, and nice dry kindling and paper at the top. (Tie newspaper in a “Nantucket knot” to get it to stay put.) Light the kindling first, get it going with a bright flame. The burning coals from the kindling and smaller wood will fall down and ignite the larger stuff; and the flames above will catch and burn the smoke from the smoldering logs.
The candle-style fire is recommended for masonry heaters and most wood stoves.
Grid fires in general are used when you want to fill a box and burn a lot of wood at once, or to make a big batch of large coals for extended campfire cooking or pit-roasts.  (For quicker grilling or cooking tasks, see the "chimney fire," below.)


Tipi Fire:
Another candle-like fire design, for campers, is the old scouting “tipi” fire.  I've seen it done magnificently by Forest Service personnel, but I've also seen it serve as a frustrating distraction that takes hours to assemble successfully.  (A useful option if you are a scout leader needing to keep the kids busy while you unpack or tend to other things, but not so great if you are out with friends you want to impress with your woodsman skills.)
Tipi fire
- clean, but tricky:
Sometimes it behaves
(like this);

Sometimes it collapses (like this).
If you have a lot of experience, or a big stone fire back to lean things against, or approximately one brave child per stick, the tipi fire works great.  It is often used for storytelling, entertainment, or signalling, where you want to create a lot of light and a strong updraft.

V-fire:
Similar to the tipi, but laid on its side: the V-fire is much easier and more flexible, and is commonly used in actual tipis, Rumford fireplaces, Dakota fire pits, earthen ovens - anywhere with one distinct air/access opening.  If you want nice bright flames for hours, or if space is limited, use a “V” fire.
Laying the V-fire


Bring the ends of some sticks together, like a sloppy corner on a split-rail fence. If you have your back to the wind, the sticks will naturally funnel the wind to the heart of the fire, and the stacked ends support the flames like a chimney. Lean kindling up inside this V and light it with tinder in the center. Your burning log ends deliver their smoky fuel right to the heart of the fire, and you can gradually feed in more wood from the cool ends as the fire burns – or even grab two sticks in each hand and move the fire somewhere else.

You can burn long sticks or logs this way on a camp fire, just watch out they don't get left burning where they can roll away outside the fire circle. This is a great fire for ovens, for most cookstoves, for Rumford fireplaces (you can light a small fire in one corner, or a big fire leaning against the whole back of the fireplace), and for campfire storytelling.

"Chimney" fire -
a vertical fire chamber
to concentrate heat & draft
Chimney Fire:
Then there's the “chimney fire,” or primitive rocket stove.  A creosote fire in your actual chimney is a dangerous nightmare, but the same powerful forces can be very useful for fast-starting your barbecue or boiling some tea or coffee.
You can actually make the combustible "chimney" with nothing but wood (see our 3 Mini Stoves document), but most people do it with steel cans.

Take both lids off a coffee can, punch a few holes near the bottom, and fill it with paper and kindling. Light it with a match from underneath or a hole in the side, and as the sticks start to burn down, fill the space with briquettes or charcoal from previous fires. The “chimney” keeps the fire together, the holes let air in to feed it, and very quickly all the sticks become glowing coals for roasting things. Dump the coals out onto a bed of ash in the bottom of the grill when you are ready to cook, or the coals will be gone before you get a chance to use them. To boil water on high heat, put the pot right on top of the “chimney” and use it like a stove; you'll need a big enough hole at the bottom to keep feeding in more wood for extended cooking.
There are a lot of rocket stoves for camping or cooking that are basically like this, with a little side opening to feed in more wood. Ideally they are insulated with fire-proof insulation, or wood ash, but sometimes people don't even add any insulation and still call it a "rocket stove."

All the above appear in our booklet The Art of Fire, some in greater detail (there's a stick-by-stick view of the V-fire, for instance.)


In a rocket mass-heater's J-shaped firebox, we apply the same principles to lighting the fire.  We run a candle or "upside-down" fire, but sideways/upside down.  (Clear as mud, right?)

Rocket mass heater:
J-style firebox.
Sticks never go down the tunnel,
only the occasional priming paper.

Once the fire is going,
larger fuel is added behind,
so its smoke/gas output is
drawn through the clean flame.
In the J-style firebox, fuel is fed vertically into a short firebox, then the flames are pulled sideways down a burn tunnel toward the taller "heat riser" or internal, firebox chimney.

All new fuel is colder than the fire, so where do we need to load it to keep the fire burning bright and hot?
We keep the burning fuels forward (I use long barbecue tongs for this), and load new logs from the room side, behind and above the hot coals and flames.
The volatile gases from the new wood get warmed up, mixed with incoming air, and finally ignited as they reach the flame party in the burn tunnel. Within a few minutes, the lower ends of the new logs will be fully involved, but the fire stays where it should be, and does not creep back up the colder ends of the sticks.

Of course, there are many other ways to lay a fire for particular purposes.  As you reconfigure for your own needs, keep in mind the key ideas that all these layouts have in common:
-Keep the flames hot and concentrated.
-Don't interrupt the flames with cold wood: instead, bring the new fuel in from “behind” the fire.  This can be from underneath, from the side, or from wherever the air intake happens to be.

This approach is super-helpful for reducing smoke and creosote, and getting the full benefit out of the work you put into fueling and tending the fire.
A really advanced approach to these efficient fire-paths is demonstrated in “circular kilns,” which are a fun reading topic in their own right.


A lot of people seem to be convinced that wood heat will always, inevitably, make a lot of dirty smoke. After seeing yellow and brown haze over wood-heated cities, these same people are convinced that electric, gas, or oil heat is “clean.” (And that's a whole 'nother rant. Our current fossil-fueled grid is subsidized to hide the true costs, and leaves our communities vulnerable to utility blackouts and economic manipulation.)

It's true that areas with a lot of wood burning stoves often have major smoke issues.
Is that because operators just don't know about the stuff above?
Or is it because they are deliberately doing the opposite?

The really big issue in smoke pollution is trying to run a slow fire, unattended, for the 6 to 8 hours to get a decent night's sleep. An experienced operator can make even a new, certified woodstove burn dirty and inefficient if they are determined to do so. This is dangerous not just because of the risk of creosote fires from all that smoke, but because the fire itself is burning unattended, with all sorts of natural variables at play.

In rocket mass heaters, we have the ultimate trick for solving that problem, permanently. I bet you already know what I mean, but there are ways to use thermal mass for greater comfort and efficiency with a wide range of stoves and heaters.
This is already quite a long post, so I'll save that for our next one.

Are these kinds of general fire tips useful?
Or do you have a specific question or topic you'd like us to address?

As always, you can leave a comment here on the blog, via email, or on our Facebook page (Ernie And Erica Wisner).

Yours,
Erica W