OPTIMUM STOVE BURNING**

Question:

"Should a stove owner EVER use unseasoned wood?  If so, is it better to burn unseasoned wood with the vents wide open, or use dry, seasoned wood with the vents shut down?  If we burn the dry wood wide open, the stove gets too hot and the wood burns too quick. Is the best solution to mix unseasoned wood with seasoned wood?"

P.S. "What temperature range is good?"

Answer:

A woodstove or fireplace insert owner should NEVER use wet or unseasoned wood! When you add a piece of wet fuel wood to your fire, the water contained in the wet wood heats up and turns into steam. This mixes with the exhaust gases and extinguishes essential secondary combustion! Secondary combustion is a primary source of heat in all newer stove systems! Regardless of how sophisticated your stove system is, using wet or unseasoned wood will cut down your stove's heat output by at least 50%!

"We have burned 61 different models of wood stove's and fireplace inserts on our test flues over the years. Also, we have kept careful records of how stoves perform in the field. We record our observations of how much creosote we take out of each chimney during our annual chimney inspection and cleaning. We also use customer-supplied performance data.

Our experience shows beyond a doubt that using ANY WET FUEL WOOD AT ALL provides MUCH LESS heat, and causes MUCH MORE creosote to form in the chimney, regardless of the draft-control setting!

Here's why:

Airtight wood stoves extract heat from wood in two ways. The first source of heat from wood is the initial, or primary combustion of the wood. This is the fire you see first. But, the secondary source of heat: is the combustion of those gasses which are released unburned from the primary fire. This secondary gas, (which looks like smoke), is loaded with usable fuel. This fuel is vaporized creosote itself. If your stove can ignite and burn this secondary flue gas before it goes up the chimney, you can literally double or triple the heat out put of your stove!

Unless yours is a very primitive model, you'll find a baffle plate of some kind near the top of your stove. It's between the fire chamber and the flue outlet. This is where the secondary burn occurs. This is where your stove creates a HUGE percentage of the heat it delivers to you! When the secondary gasses are ignited, the internal temperature of the stove may go from 450 degree's to 1600 degree's! That is a HUGE performance increase! But, it DOES NOT mean the wood will burn up faster! Such high temperatures create a powerful vacuum inside your stove. You only need a very small intake hole, (e.g. 1/2 inch in diameter) to provide oxygen. That small intake port provides a high pressure, but very small stream of oxygen which enables you to burn your stove very hot, for a long time. By controlling the amount of oxygen that enters the stove, you prohibit the stove from burning the wood too fast.  Even though it is burning much hotter, you can actually burn the wood you do use for a longer period. The amount of secondary combustion that occurs varies widely from model to model. Largely due to advances in heat extraction technology over the years. A twelve-year-old baffled airtight stove can be presumed to operate at about 40% efficiency, while many of today's EPA approved wood stoves exceed 80% efficiency. The main difference between the older wood stoves and today's wood stoves is in the upper baffle chamber, where newer techniques have been incorporated to re-burn and use the secondary exhaust gases.

When you add a piece of wet fuelwood to your fire, the water contained in the wet wood heats up and turns to steam. This mixes with the exhaust gases and extinguishes the essential secondary combustion! Regardless of how sophisticated your baffle system is, this cuts your heat output by at least 50%! Plus, it results in cool, water-laden exhaust, filled with unburned vaporized creosote, carbon monoxide particles and other polluting exhaust gases. This wet, heavy, high-density smoke travels very slowly up the chimney, where it cools even further. This causes excessive creosote formation. (Creosote condenses in your flue like a hot breath on a cold mirror: out of the wood smoke as it cools). Excessive creosote formation causes chimney fires. So, when you burn wet wood, you dramatically DECREASE your heat output, while you dramatically INCREASE the likelihood of a chimney fire!

Go ahead and turn the draft control down. This actually creates maximum heat output and increases burn time, but be careful not to smolder the fire. If your stove has a viewing window, you can easily see if you're starving the fire for air: because the flame goes out. If you don't have a viewing window, attach a flue gas thermometer to the stovepipe, 18" to 24" above the stove, and keep the temperature above 325 degrees. Remember, oxygen is required to ignite the gases in the secondary combustion chamber, so if you take away too much air by adjusting your draft control too low, you'll lose the benefits of the secondary burn even if your fuelwood is dry. This will evidence itself on the flue gas thermometer, which will quickly fall into the marked creosote zone.

Today's EPA approved wood stoves provide pre-heated oxygen to the secondary burn chamber directly, through a separate intake controlled by the chimney updraft, enabling you to turn your draft control all the way down to control the primary fire without extinguishing the secondary burn. This technology results in fewer particulate emissions, longer burn times and cleaner chimneys, but it is important to remember that steam is still not combustible: even in these state-of-the-art stoves.  They can't burn the gases in the secondary combustion chamber if the fuelwood is wet!"*

*This article was paraphrased from a correspondence with Tom Oyen "The Chimney Sweep Inc." You can visit Tom's site at: http://www.nas.com/~chimneysweep  We acknowledge Tom's contribution with gratitude.

** This article only applies to stoves, or inserts that are vented properly. In most cases that means the flue can be no larger than 8 inches in diameter. Smaller is better. If your insert is unlined, you will never get the performance mentioned here. If a flue system is too large, the flue temperatures can never get hot enough to provide the draw (vacuum) necessary to sustain secondary combustion.

1-800-SWEEP-31       1-800-793-3731