Vermont Casting 410 Single Venting, Fuel, Backpuffing, Negative Pressure, Conclusion

There should be no more than eight feet of single-wall stove pipe between the stove and a chimney. Longer runs can cool the smoke enough to cause draft and creosote problems. Use double-wall stove pipe for longer runs.

Single Venting

Your stove requires a dedicated flue. Do not connect the stove to a flue used by any other appliance. Chimney draft is a natural form of energy and follows the path of least resistance. If the stove is vented to a flue that also serves an open fireplace or another appliance, the draft will also pull air in through those avenues. The additional air flow will lower flue tem- peratures, reduce draft strength and promote creosote development; overall stove performance will suffer. The effect is similar to that of a vacuum cleaner with a hole in the hose. In some extreme instances, the other appliance can even impose a negative draft and result in a dangerous draft reversal.

Fuel

Even the best stove installation will not perform well if poor fuel is used. If available, always use hardwood that has been air-dried (‘seasoned’) 12-18 months. Softwood burns more rapidly than hardwood and has a high resin content conducive to creosote production. Decayed wood of any type has little heat value and should not be used.

All unseasoned (‘green’) wood has a high moisture content. Much of its heat value will be used to evapo- rate moisture before the wood can burn. This signifi- cantly reduces not only the amount of energy available to warm your home, but also the intensity of the fire and temperature of the exhaust gas. Incomplete combustion and cool flue temperatures promote creosote formation and weak draft.

You can judge the moisture content of wood by its appearance and weight or use a commercially avail- able moisture meter for an exact measurement. Unseasoned wood will be a third heavier than dry wood. Also, look for cracks (‘checking’) in the ends of the log that result from contraction as the wood dries. The longer and wider the cracks, the dryer the wood is. Purchase your fuel from a reputable dealer.

Creosote

Creosote is a by-product of low-temperature stove operations, weak draft or both. It is a tar that results when unburned gases condense inside the flue system at temperatures below 290°F. Creosote is volatile and can generate chimney fire. All of the installation characteristics that adversely affect chimney draft also promote creosote condensation. Consequently, you can minimize creosote accumulation with an effective

Madison Woodburning Stove

chimney design and the use of operational techniques that encourage good draft and complete combustion.

Backpuffing

Backpuffing is a condition that results when the draft is too weak to pull flue gases out of the chimney system as fast as the fire is generating more. Volatile gases build up within the firebox until reaching a density and temperature at which they ignite. With this ignition, you may hear a muffled popping sound and see a bit of smoke forced out of the air inlets.

This condition is most likely to occur in the spring or fall when moderate outdoor temperatures and low intensity fires combine to inhibit draft strength. If your stove backpuffs, open the air inlets to induce a livelier fire and speed airflow through the stove. Avoid large loads of firewood at one time. You should always see lively, dancing flames in the firebox; a lazy, smoky fire is inefficient and will promote draft problems.

Negative Pressure

Good draft also depends on a sufficient supply of air to the stove. The chimney cannot pull more air than is available. Sluggish draft can be caused by a house that is tight enough to prevent the ready flow of air to the stove, or by competition between the stove and other appliances that vent indoor air to the outside; i.e., exhaust fans for range hoods, clothes dryers, bath- room, etc. If the chimney draws well when all such equipment is turned off (or sealed, in the case of the fireplaces and/or other stoves), you simply need to be attentive in timing the use of the other appliances. If you need to crack a nearby window or door to enable the chimney to pull well, you should install an outside- air intake to bring combustion air directly to the stove. Consult your Vermont Castings dealer regarding an adapter to attach to the stove to connect an air duct for outdoor combustion air.

Conclusion

Woodburning is more an art than a science. Art in- cludes technique and since installations, homes and fuel vary, the stove operator must also vary technique, (mostly timing), to achieve satisfying results. Over time, you will become familiar with the intricacies and nuances of your particular installation and you will be able to identify cause and effect in a variety of sea- sonal circumstances.

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