Vermont Casting 1610 Single Venting, Creosote, Fuel, Back-puffing, Draft Testing, 30002850

transfer, and it gives you long-term flexibility for install- ing a different stove without relocating the thimble. There should be no more than eight feet of single-wall stove pipe between the stove and a chimney; longer runs can cool the exhaust enough to cause draft and creosote problems. With prefabricated chimney, bring it down to six to eight feet from the stove. With a masonry chimney, arrange the pipe so that it turns into the chim- ney within eight feet of the stove.

Single Venting

Each ‘airtight’ stove requires its own flue. If an airtight stove is vented to a flue that also serves an open fire- place, or a leakier stove, it’s easier for the chimney draft to pull air in through those channels and performance of the stove suffers. Imagine a vacuum cleaner with a hole in the hose to understand the effect here. In some cases the other appliance can even cause a negative draft through the stove, and result in a dangerous draft reversal.

Creosote

Creosote is a by-product of slow wood-burning. It’s an organic tar that can condense in the flue if it is pres- ent in the exhaust, slow-moving, and cools to less than 290°F (130°C). Condensed creosote is volatile, and can generate chimney fires if it gets hot enough. All the features that affect chimney draft also affect creosote condensation - so use whatever combination of installa- tion features and operational steps that will encourage good draft and minimize creosote production.

Because letting the exhaust cool off and slow down is one of the keys to creosote accumulation, it makes sense to line a chimney to match the stove’s outlet size, for safety reasons as well as performance. Canadian law requires a matching liner to serve any stove or insert vented through a fireplace chimney; in the US, the National Fire Protection Association (NFPA) recom- mends a chimney liner if the flue is more than three times bigger (in square area) than the outlet on the stove or insert. Some localities enforce the NFPA guide- lines as part of their building codes.

Fuel

Even the best stove installation will not perform well with poor fuel. The best fuel is hardwood that has air- dried 12-18 months. Softwood burns, but not as long as hardwood. ‘Green’ wood has a lot of moisture in it; it will burn, but some of the heat potential is used to boil the extra moisture from the wood. This reduces the amount of heat that reaches your home and can contribute to a creosote problem. There are moisture meters available for firewood; you can also judge your wood by its ap- pearance and weight. If you get it green, lift a piece and

Defiant 1610 Non-Catalytic Woodburning Stove

get a sense of its weight; it can lose a third or more of its weight as it dries. Also look at the ends of a log; as it dries it shrinks and often cracks. The more weathered and cracked a piece is, the drier it is.

Dry wood burns readily with a good chimney draft. But with modern stoves, wood can be too dry and too volatile. Smoke and combustible gases can ‘gas out’ from the wood quickly and densely enough to overload the combustion system. If you hear a rumbling or roar- ing noise (like a propane torch) from the stove, that is a sign that the stove is overfiring.

Back-puffing

Back-puffing results when the fire produces volatile gases faster than the chimney draft pulls them out of the firebox. The gases back up in the firebox until they are concentrated enough and hot enough to ignite. If your stove back-puffs, the stove needs to cool down. You should open the damper to let the smoke rise to the flue more quickly, allow more air into the firebox, avoid big loads of firewood and check that the wood moisture is not too low.

Draft Testing

An easy way to test your chimney draft is to close the stove’s damper, wait a few minutes to let the airflow stabilize, then see whether you can vary the strength of the fire by swinging the air control open and closed. Re- sults are not always instant; you may need to wait a few minutes for a change in the air control setting to have an effect on the fire. If there’s no change, then the draft isn’t strong enough yet to let you close the damper, and you’ll need to open it for awhile longer and manage the fire with the air inlet until the draft strengthens. If you keep track of your burning habits and relate them to their effects on the stove’s operation, you’ll be rewarded with good performance and a safe system.

Negative Pressure

Good draft also depends on a supply of air to the stove; a chimney can’t pull in more air than is avail- able to it. Sluggish draft results when a house is tight enough to prevent the ready flow of air to the stove, or by competition between the stove and other equipment that sends indoor air outside - especially power-driven equipment like range hoods, clothes dryers, etc. If the chimney draws well with all other equipment turned off (or sealed, in the case of fireplaces and/or other stoves), then you simply need to be careful with timing the use of the other air consuming equipment. If you need to crack a nearby window or door to enable the chimney to flow well, it may be a good idea to install an outside-air intake to bring combustion air directly to the stove. An outside air kit is available to connect the stove directly to a source of outdoor combustion air.

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