Turn Your Fire Upside-Down
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Modern EPA Certified wood burning appliances are designed to burn wood with minimal emissions. But it’s possible to burn wood cleanly and efficiently in a fireplace or a fire pit. Taking a little time to lay a top burn fire will result in a long burning fire that releases fewer emissions into the air.
To burn wood with minimal emissions, you must have a fire that burns hot enough to burn the gases created when gasifying the wood. There are a number of things you can do to make a fire that burns as completely as possible.
1. It is essential that the wood you use to build the fire be dry. Freshly cut wood can contain up to 50% moisture by weight. Properly cured firewood should contain no more than 20% moisture. If you put wet wood in your fire, the excess moisture must be boiled out of the wood before it can ignite. This robs your fire of heat and causes it to release more pollutants into the atmosphere.
2. Remove the grate from your fireplace and build the fire on the floor of the fireplace. When you burn wood, anytime, any method, 60% to 80% of the fuel is driven off as flammable gasses. If you burn this wood in an “airtight stove,” nearly all of that fuel goes up the chimney unburned, and is dumped into a cool flue, and condenses out as creosote. When burned in a fireplace on a grate, with kindling or gas lighter below, a big share, but not all of this gas goes unburned. The flames you see are gasses burning, but by starting it from below, the fire is driving the gasses off ahead of the fire, so a lot of them get away without burning. The fire also engulfs the wood as fast as it can, so the wood load burns rapidly. Elevating the fire pulls cold air into the firebox, cooling the fire and carrying these flammable gases up the chimney. This keeps the flue from achieving optimal temperatures and causes flammable gases to condense on the walls of the flue as creosote. The remainder of these gases carry irritating air pollutants into the air of your neighborhood.
When you lay your fire directly on the hearth, and light it at the top, you change a lot of the dynamics, and produce the results detailed further down the page.
3. Build the fire upside-down. To make a successful upside-down fire, you’ll need firewood in several different sizes. The largest, longest pieces of wood should be placed on the floor of the fireplace to form a base for the fire. Lay these logs side by side and as close together as you can get them. Lay another layer of wood on top of the base layer, at a right angle to the wood of the layer below. This wood should be smaller in diameter and shorter than the wood in the previous layer. Proceed upward with successively shorter and smaller pieces of wood for each layer. After three or four layers of firewood, place four to six layers of pencil sized kindling on top of your fire lay. Add a handful of cedar shavings or other fire starting material to the top and light the fire at the top.
A fire built in this manner will burn nearly all of its smoke, resulting in a dramatic decrease in neighborhood air pollutants. Because smoke is fuel that is typically unburned, burning it will give you a longer lasting fire. It is not unusual to have an upside-down fire burn for four or more hours before you have to add any wood to it.
For more information on building Upside-Down Fires, download the following documents for reference.