Ensure safety first, then higher efficiency is possible

To operate your wood heating system efficiently, you must have confidence that it is safe. Efficient operation means burning each load of wood hot for a short period. Worries about safety can force you to keep temperatures too low, which leads to low efficiency, high pollution and the potential for chimney fires. Have your system inspected by a qualified technician and upgrade it to meet safety codes before using the tips provided here. If you live in the US, contact the National Fireplace Institute to find a qualified technician near you. If you live in Canada, contact Wood Energy Technology Transfer Inc. to find a qualified technician near you.

How to buy or prepare good firewood

Whatever wood species you use, it will burn more efficiently and be more convenient to use if it is properly seasoned. Here are some tips for firewood preparation.

1.    Very hard woods like oak and maple are good fuel for long burns in very cold weather, but not as good for the relatively mild weather in spring and fall because their high density makes controlling heat output more difficult.

2.    Softer woods like poplar, aspen, willow, spruce and pine are better when heat demand is low because they light easily, burn quickly and don't leave a long lasting charcoal bed.

3.    The lighter firewood species should be processed in early spring to be ready for burning that fall. However, hard woods like oak and maple take more than a full year to season, except in arid climates. Drying in damp maritime climates takes longer.

Img1-cutolength4.    Piece length should be about 3" shorter than the firebox.

5.    Shorter pieces are easier to handle and make fire maintenance easier; 14" to 16" is a good length.

6.    Split the pieces into a variety of sizes, from 3" to 6" at the largest cross sectional dimension. Most commercial firewood is not split small enough for convenient fire management. 

Img2-split7.    The larger the stove or furnace, the larger the pieces can be, but never larger than 8" diameter.

8.    Tree tops and wind falls can be used for firewood down to less than 2" diameter.

9.    Never leave firewood in a pile on the ground for more than a couple of days. Wet wood on the ground quickly attracts bugs and mold.

Img3-windsun10.   Wood should be stacked in an open area exposed to sun and wind for the summer. Green wood will not season properly in a wood shed or in deep shade.

11.   Stack wood on rails to keep it off the ground.

12.   The triangular shape of split pieces wedge together as they are stacked and help to make the pile stable.

13.   The more quickly the surface of the pieces dries, the less chance there is of molding and bug infestation.

14.   Cover just the tops of firewood stacks.

15.   Avoid stacking more than four feet high because tall piles become unstable.

16.   Shorter firewood pieces (12" - 14") make for narrow tippy stacks; use sticks propped against each side of the piles so wind doesn't blow them over.

17.   When seasoned, usually by late September, the wood can be moved to winter bulk storage where it should be fully sheltered from rain and snow.

18.   The ideal winter storage is close to, but not inside, the house.

19.   Avoid storing large amounts of wood in the house because mold spores and moisture can affect indoor air quality, a potential problem for people with asthma and other lung diseases.

20.   Bring in wood to warm up before burning, but only a few day's supply at a time.

How to build foolproof wood fires

1.    The function of the kindling fire is to quickly heat up the chimney and the brick and steel of the firebox to create the environment for a stable, brightly burning fire, without having to open the loading door several times to adjust it.

2.    The edges of firewood pieces heat up and ignite first. The more edges close together in your kindling fire, the faster it will ignite. Do not use unsplit rounds when starting a fire because they don't have edges so they are slow to ignite.

3.    Softer woods like pine, cedar, spruce and poplar make better kindling than harder woods because they are easier to split up fine and they light more readily.

4.    Logs from which kindling is split can be cut as short as six inches to make splitting and fire building easier. Straight grain conifers like cedar and pine work well as kindling.

5.    Before building a fire, remove excess ash from the firebox; never let ash build up to more than two inches.

6.    Open the air control(s) fully and open the bypass damper if the appliance has one.

7.    When building a kindling fire, avoid a structure that collapses, smothering a struggling fire. Following are two popular approaches to avoiding the collapsed kindling fire.

Img4-topdown2A top down fire ready to light.

8.    Two parallel logs: Place two split logs parallel to each other in the firebox with a space between. Fill the space with newspaper and fine kindling and place several larger kindling pieces crosswise on top. Light the paper.

9.    Top down fire: Place a layer of standard firewood pieces first, a few pieces of heavy kindling next, and finally, fine kindling. Roll up single sheets of newspaper corner to corner, tie a loose knot in each and place four or five on top of or in front of the kindling. Light the paper. This type of kindling fire can provide two or more hours of effective heating without having to open the door to add wood or adjust the fire.

10.   Leave combustion air inlets wide open at least until the firebox is full of flame and the wood is charred black and the edges are glowing red.

How to maintain wood fires for heating efficiency

1.    The objective in maintaining wood fires is to prevent the wood from smoldering because any smoke that passes out of the firebox will condense as creosote in the chimney and/or be emitted outdoors as air pollution. Smoke is not a normal byproduct of wood combustion. Smoke is waste resulting from poor combustion. There will be no visible smoke from your chimney if the wood burns with bright, active flames.

2.    After an overnight fire you will find remaining coals at the back of the firebox, furthest from the combustion air inlet. This is the time to remove a small amount of this ash.

Img5-ashrake1Ash at front; coals at rear. Img6-ashrake2Remove ash. Img7-ashrake3Rake coals.

3.    Avoid spreading the charcoal out evenly and placing the new load of wood on top because this can lead to extended smoldering before the wood ignites.

4.    Find where the combustion air enters the firebox; for most stoves, fireplaces and furnaces this is at the front where the loading door is. Rake the coals toward the air inlet. Place the wood on and behind the coals.

5.    Pokers are for decorative fireplaces. A properly-built heating fire should not need poking.

6.    A rake is the best stoking tool for heating fireplaces, stoves and furnaces. A simple rake can be made from a 3/8" steel rod 20" - 25" long with a 1/8" thick steel rectangle measuring 1 1/2" x 3 1/2" welded to the end.

7.    About 1/5th of the heat from the burning wood should be given to the chimney to produce strong, stable draft, the pressure difference which drives the system. Efforts to prevent heat "loss" to the chimney are counterproductive because they lead to wasteful and dangerous smoldering.

8.    Avoid adding a log each hour in the attempt to produce a steady heat output. Wood burns best in cycles. A cycle begins when a new load of wood is placed on and behind a coal bed and ends when that wood is reduced to a similar-sized coal bed.

9.    To produce low heat output in mild weather, use small loads of soft wood placed in a crisscross formation.

Img9-FireeastwestEast-west log orientation.10.   To produce high heat output in cold weather, use larger loads of hard wood placed compactly in the firebox.

11.   Long burn times are not an indication of efficiency or effectiveness. In fact, peak efficiency and heating effectiveness are usually achieved with burn cycles of eight hours or less.

12.   If your firebox floor is roughly square, you can load the wood east-west so the combustion air reaches the side of the logs, or north-south so the air approaches the ends of the logs. An east-west load breaks down more slowly, so is a good orientation for overnight fires in spring and fall when heat demand is low. A north-south load can be larger, but breaks down more quickly, so it is good for high output, long lasting fires in cold weather.

Img10-FirenorthsouthNorth-south log orientation.13.   When rekindling from coals, rake the coals towards the air inlet, place fuel behind the coals, and always place the smallest, driest piece of firewood directly on the coal be to act as the 'igniter'. Your igniter should begin flaming almost immediately and as it burns it will ignite the larger pieces.

14.   Leave the air control wide open until the firebox is full of flame, the new wood is charred black and the edges are glowing red. Turn down in two or three stages.

Dealing with wood ashes

1.    Remove a small amount of ash frequently. During 24 hour heating in cold weather, it may be appropriate to remove a small amount of ash each morning before the new fire is kindled to make raking coals and kindling loads throughout the day more convenient.

2.    Ashes often contain live coals which can stay hot and give off carbon monoxide for days. So, put ashes in a metal container with a lid and place the container outside the house and away from combustible material.

3.    Some ash can be used as a lawn and garden fertilizer to provide soil nutrients and reduce acidity. It can be used on compost piles to maintain neutral acidity levels. Some people use ashes to provide traction on icy driveways and sidewalks. Excess wood ash can be taken to garbage disposal sites.

The biggest single efficiency booster: upgrade to an EPA certified stove

Img11-epalogo1.    Although the EPA wood heater certification program was created to reduce air pollution, it resulted in added benefits like higher efficiency and increased safety. On average, EPA certified stoves, fireplace inserts and fireplaces are one-third more efficient than older conventional models. That's one-third less cost if you buy your wood and a lot less work if you process your own.  

2.    Because advanced technology EPA certified heaters burn the smoke before it leaves the firebox, they extract more of the energy in the wood. This results in higher efficiency and less air pollution in your neighborhood.

3.    Less smoke in the flue gas means less creosote (which is condensed smoke) in your chimney. Using an advanced technology wood heater reduces maintenance costs because your chimney will need sweeping less often.

4.    The chimney deposits that do accumulate are much less combustible, which greatly reduces the chance of having a dangerous chimney fire.

5.    EPA certified heaters are easier to use because their fires ignite and burn more reliably.


Gulland Associates Inc. 2004

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