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Maintaining Wood Fires for Heating Efficiency

Maintaining Wood Fires for Heating Efficiency

Smoke with Black Background

How to maintain wood fires for heating efficiency


  • The goal 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 or be released outdoors as air pollution. Smoke is not a normal byproduct of wood combustion but is waste resulting from poor combustion. There will be little or no visible smoke from your chimney if the wood burns with bright, active flames.
  • After an overnight fire you will find the remaining coals at the back of the firebox, furthest from the combustion air inlet. This is the time to remove a small amount of ash.
  • 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.
  • 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.
  • Pokers are for decorative fireplaces. A properly-built heating fire should not need poking.
  • 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.
  • About 1/5th of the heat from the burning wood should be given to the chimney to produce strong, stable draft. Draft is the pressure difference that drives the flow of air and gases through the system. Efforts to prevent heat “loss” to the chimney are mistaken because they lead to wasteful and dangerous smoldering.
  • 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.
  • To produce low heat output in mild weather, use small loads of soft wood placed in a crisscross formation.
  • To produce high heat output in cold weather, use larger loads of hard wood placed compactly in the firebox.
  • 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.
  • 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 arrangement 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.
  • 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 bed to act as the ‘igniter’. Your igniter should begin flaming almost immediately and as it burns it will ignite the larger pieces.
  • 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 the air in two or three stages.

Dealing with wood ashes

  • Remove a small amount of ash frequently. During 24 hour heating in cold weather, a small amount of ash can be removed as often as each morning before the new fire is kindled to make raking coals and kindling loads throughout the day more convenient.
  • 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 on a concrete surface and away from combustible material.
  • Some ash can be used as a lawn and garden additive 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

  • Although the EPA test for wood stoves 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.
  • Because advanced technology EPA certified stoves, fireplaces and furnaces burn the smoke before it leaves the firebox, they release more of the energy in the wood to the house. This results in higher efficiency and less air pollution in your neighborhood.
  • Less smoke in the flue gas means less creosote (which is condensed smoke) in your chimney. Using an advanced technology wood stove reduces maintenance costs because your chimney will need sweeping less often.
  • The chimney deposits that do accumulate are much less combustible, which greatly reduces the chance of having a dangerous chimney fire.
  • EPA certified heaters are easier to use because their fires ignite and burn more reliably.


Created by Gulland Associates Inc.

For more information please visit www.woodheat.org