Practical Tips for Efficient Wood Heating

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Photo by Fotolia/Broker
It’s a good idea to take advantage of thermal mass by placing your woodstove near dense building materials such as bricks, stone or concrete. These materials slowly absorb and then release heat.

Save time, energy and money with these tips for efficient wood heating to get the most out of a woodstove. If you decide to heat your home with wood there are a few tips and tricks to consider.

Practical Tips for Efficient Wood Heating

Considering the amount of work involved in full-time wood heating, it just makes sense to burn efficient fires. The payoff is lower cost if you buy your wood and less work if you process your own. When you make smoky fires a thing of the past, you’ll never again worry about flammable creosote causing chimney fires, and you’ll need to sweep the chimney less often. The door glass of your stove or fireplace will stay clear longer, and there will be less chance of smoke roll-out when you open the loading door.

Let’s see: lower cost, less worry, less maintenance and better indoor air quality. Do those advantages make it worth your time to try out some new wood heating skills? I thought so.

The secret to high efficiency wood heating is to pay attention to the smoke. When a piece of firewood is heated, it begins to smoke. The smoke is made up of sticky tar droplets and some combustible gases. If a piece of wood were heated and allowed to smoke until only charcoal remained, more than half of its energy content would be gone — up in smoke, you might say. It is important to burn the smoke because any that escapes from the firebox unburned is wasted fuel that will stick in the chimney as creosote or be released as air pollution. Wood smoke is not a normal byproduct of wood combustion, it is waste. Visible smoke at the top of a chimney is always a sign that energy is being wasted.

Tips for Lighting the Fire

Starting a wood fire can be a frustrating experience, and when a fire fails to catch it can even be embarrassing if anyone is watching. But, by using the right techniques and materials, you can have complete confidence that every fire you light will take off immediately and burn reliably.

First, consider a key rule that applies to all wood burning: The wood must be dry. No fire will light and burn reliably if the wood is damp. By dry, I mean that the wood’s moisture content must be less than 20 percent.

Is the wood dry enough to burn? Here are several ways you can tell:

  • Look for checks or cracks that form at the ends of the pieces as wood dries.
  • Consider the color. Wood darkens as it ages, from white or cream color to gray or yellow.
  • Split a piece, and if the fresh surface feels warm and dry, it is dry enough. If it feels cool and damp it is too wet.
  • Bang two pieces together: seasoned wood sounds hollow, wet wood sounds dull.
  • Burn some: wet wood sizzles and bubbles at the ends and dry wood doesn’t.

The old way to light a wood fire is to bunch up some newspaper, place some finely split kindling on it, put some bigger pieces on that and light the paper. This “bottom-up” approach can work provided enough paper and fine kindling are used. However, this method has two serious drawbacks. First, as the paper burns the pile will collapse and the fire might smother itself. Second, you have to keep opening the stove door to add more wood until you have a respectable fire. I don’t recommend this method because it is too smoky, labor intensive and messy.

Here are three ways to light a fire that I think work better:

  • Two parallel logs. This is a popular method because the fire can’t collapse and smother itself. Place two split logs in the firebox and put some twisted newspaper between them. Add some fine kindling — 1 inch square or less — on the newspaper and more kindling of various sizes across the two logs. This method works well because the two logs give some space for the newspaper and kindling to get a good start. Their burning is usually enough to ignite the two larger logs. After the kindling has almost burned out, more wood must be added to make a full fire.
  • Top down. This is my favorite method. It is absolutely reliable, and when it is done properly there is almost no smoke right from the start. The other great thing about this method is that the fire puts on a show that is guaranteed to surprise, delight and impress anyone who happens to be watching. Just place three or four split logs on the firebox floor. Place six or eight pieces of medium kindling across them. Then put 10 or so pieces of fine kindling across the heavier kindling. Now take four or five full sheets of newspaper and roll each one up corner-to-corner and tie a sloppy knot in it. Knotting the paper helps to keep it from rolling around as it burns. Place the knots on top of the fine kindling. Light the paper and watch as the fire burns down through the light kindling, the heavy kindling and into the bottom logs. Using the top-down method, you can light the paper, close the loading door and relax for up to two hours before it is time to reload.
  • Using fire starters. Many people use fire starters made of sawdust and paraffin wax. You can buy commercial versions or make them yourself. You can even cut up a wax fire log to make starters, or try candle stubs. If the starters are placed within a nest of dry kindling, the fire will start reliably.

No matter which method you choose, as you light the fire, you should open the air control completely. If the fire struggles, either because the stove has a restrictive air control or because the chimney and flue pipe arrangement is less than ideal, you can leave the door open a crack until the fire catches. Don’t leave the stove unattended with the door unlatched because the fire could get out of control.

The kindling fire should accomplish a few goals. It should heat up the chimney to produce strong, stable draft. It should heat up the brick and steel of the firebox to create an environment for clean burning fire. And it should heat the pieces of fuel until a thick layer of glowing char forms. To achieve these goals, leave the air control fully open until the firebox is full of flame and a charcoal layer forms on the wood. It is best to turn the air down in a couple of stages so the fire has a chance to recover from each reduction. If the fire loses most of its flame when you turn down the air control, open it again until the fire recovers before trying again.

Managing the Woodstove Blaze

After you have started the fire, here are some strategies you can use to keep it burning as efficiently as possible.

Burn in cycles. Wood fires burn best in cycles, so it’s not a good idea to add a log every hour to attempt to produce an even heat output. The trouble with that approach is that a single log will not burn cleanly because the firebox cools off too much and flaming combustion cannot be sustained. Instead, you need to add at least three pieces — and preferably more — each time you load so that the heat from one log burning can ignite and sustain the flames on the next log, and so on.

Another thing to consider is that if you have thermal mass built into the area near the heater (dense building materials such as concrete, brick or stone) these materials will absorb some of the heat from the start of a heating cycle and release it later as the fires subsides. Thermal mass and cyclical firing work together nicely.

Burn hot, bright fires. Your fires should actively flame until the wood is reduced to charcoal. If there are no flames, half the wood is being wasted as smoke. In mild weather, you can build brightly flaming fires that don’t overheat the house by splitting your firewood finely and using three or more pieces each time you load.

Before loading, rake your coal bed. The live coals left from the previous load are used to ignite the next. To do this, the main flow of combustion air must reach the charcoal first to make it burn hot, and then reach the new wood pieces. Therefore, rake the coals to where the combustion air first reaches the fire. For most stoves, fireplaces and furnaces, this is just inside the loading door. Place the new pieces on and behind the glowing charcoal. Place the smallest, driest piece of the load directly on the charcoal to act as the igniter.

Ways to Control Woodstove Heat

Everyone who heats with wood struggles with the problem of overheating the house, especially during milder weather in spring and fall. Many people reduce heat output by turning down the air control, but this approach wastes fuel because you’re not allowing the fire to burn efficiently. That means smoke is released unburned while creating a lot of creosote and air pollution. Instead, consider these five different ways to control heat output. Use as many of these techniques as you can.

  • Choose your fuel species. Use lighter, softer woods such as spruce, pine, poplar and willow in mild weather and save harder woods, such as oak and maple, for colder weather. In mild weather, you can build fires using three or more small (3 to 4 inch diameter) pieces of a soft wood and let the fire burn with the air control fully open. The softwood fire will recede within half an hour or so, and you will be left with some coals that can gently warm the space for the following couple of hours.
  • Adjust the amount of wood. Smaller loads of wood make heat output easier to control in mild weather. Larger loads are effective in cold weather to produce longer, higher output burn cycles.
  • Consider the orientation. In fireboxes that are roughly square, the wood can be loaded either east-west (through the door so you see the sides of the logs) or north-south (you see the ends of the logs). Wood placed east-west in the firebox breaks down more slowly than it would placed north-south, so this is a good orientation for extended fires in mild weather. That is, if you want an overnight fire in fall or spring, an east-west loading can help spread the low heat output and leave enough coals to rekindle the fire in the morning. In contrast, north-south placement permits more fuel to be loaded and it breaks down more quickly, which is suitable for high-output, overnight fires in cold weather.
  • Use different configurations. Pieces loaded loosely in a crisscross configuration break down quickly, so this can be a good way to build a short, hot fire just to take the chill off a space without overheating it. The opposite is compact loading, which is effective for long firing cycles, such as overnight in cold weather, because pieces packed together closely tend to break down slowly.
  • When you must, adjust the air supply. Notice that reducing air supply is only one of five ways to control heat output and that it is last on the list. Use all the other ways to reduce heat first, before turning down the air. By using the four previous methods first, you can maintain brightly flaming combustion without overheating the space or creating air pollution.

Some people assume that wood heating is simple and that the skills needed to do it well come naturally. That has not been my experience. I’ve been improving my wood heating skills steadily for more than 30 years and continue to learn new things. If you try some of the techniques suggested here, you’ll see good results almost immediately, and if you practice you’ll get better at it. Wood heating is important enough to be worth doing well.

Necessary Wood Heating Tools

A few simple tools can make life with wood heating more convenient and pleasant. One worthwhile accessory is a sturdy wood box to hold enough fuel for a day or two of heating.

Another necessity is a good tool set for managing the fire. Tool sets for woodstoves need only three things: a rake, a shovel and a brush. The rake is just a steel rod with a small steel plate (about 1 1/2 inches by 3-1/2 inches) welded to the end. Tools for heaters tend to be shorter and more robust than fireplace tool sets.

It’s also handy to have a pair of hearth gloves for protecting your hands while raking large coal beds. Hearth gloves are thick leather with a lining and are available at hearth stores or welding equipment stores.

Wood Heating System Design

Part of my work over the past 30 years has been to search for ways to squeeze more efficiency from wood heating systems. In addition to the day-to-day practices of heating with wood that are discussed in this article, you should also carefully consider the system design to be sure you’re getting the best performance possible.

  • Effective space heating with wood starts with finding a good location for the stove or fireplace. In general, a space heater should be located in the part of the house you want to be the warmest — this is usually the main floor area made up of the kitchen, dining room and living room. Locating the heater in the space where you live, rather than in a basement, can increase comfort and cut your fuel consumption up to 25 percent.
  • The space heater should be one that is certified for low emissions by the U.S. Environmental Protection Agency (EPA) because these stoves and fireplaces not only pollute less, they also deliver up to one-third higher efficiency than the old “airtight” stoves of the 1970s and ’80s.
  • For the greatest efficiency, the flue pipe and chimney should rise straight up from the appliance flue collar into the chimney, and the chimney should rise straight up through the house from there. Straight is best because every elbow or offset in the system acts as a restriction to the free flow of exhaust. Weak draft caused by elbows and horizontal runs in the flue pipe — or worst of all by a chimney that exits a wall and runs up the outside of the house — results in sluggish fires and smoke roll-out when you open the door to add wood.True, a straight up chimney installation may be a little trickier to accomplish, and it may limit your options for the exact location of the stove or fireplace, but the performance payoff is worth the effort.
  • Another thing to consider with stove placement is that a convenient route for fuel wood (from storage to hearth) should be a priority — because wood is heavy and awkward to carry and a whole winter’s supply is a large amount. The ideal is to have your winter storage on the same level as the heater so you don’t have to negotiate stairs. You could also install a wood door in a wall near the heater. A wood door has an opening outside into the wood storage area and a door inside the house. Between the doors is a space in the wall to stack a day or so of firewood. Wood doors save steps and are convenient to use. If your wood storage is on a lower level than the heater, you might consider a wood elevator, which is like an old dumbwaiter for lifting things from one level of a house to another.
  • To level out the ups and downs of heat output from a stove or fireplace, you could build thermal mass into the installation. Thermal mass is just a fancy term for materials such as brick or stone that absorb heat and release it slowly. You can add mass to a woodstove or fireplace installation by using a brick or stone wall and hearth floor coverings. If you are building a new house that will be heated mainly with a woodstove, make the wall behind the heater out of solid poured concrete. If the hearth area also receives winter sun, the mass will play a dual role in helping to cut your heating costs.

John Gulland is a MOTHER EARTH NEWS contributing editor and has written several articles on woodstoves and heating with wood. He has been a wood heating consultant for almost 30 years and is the cohost of Wood Heat.