Heating with Wood

In recent years, many people have begun to use wood for heating. Unfortunately, some have not been careful enough in installing and maintaining their heating systems. This has led to a number of serious fires, some of which have resulted in deaths.

A wood heating system is only dangerous when neglected. When properly set up and cared for, it can be a safe, economical alternative to other forms of energy.

The Heating System

The main elements in a wood heating system are the heater, the smokepipe and the chimney. The heater can be a stove, fireplace, or furnace. Some operate by simply radiating heat. In others, air is warmed by being circulated through the heater and then released back into the room.

Smoke and gases produced in the heater travel up the smokepipe to the chimney and then on up out of the house. The smokepipe is usually uninsulated, at least with stoves and fireplaces.

Causes of Fires

Most fires involving wood heat can be traced to three causes. First, they can result from the use of faulty equipment. This could be equipment that is old and worn out, such as a used stove Other times, it might be equipment that is new but unsuited to the job, such as light pipe used in place of proper stovepipe.

Second, fires can be started by heat radiating from the heater and smokpipe. For example, if the pipe is too close to the ceiling, it can set the ceiling on fire. The same can happen if the smokepipe is not properly insulated where it passes through the ceiling or wall.

Third, fires can be caused by a substance called creosote. This is formed from gases produced as the wood burns. It is highly flammable and usually collects as a sticky liquid on the inside smokepipe and chimney. If creosote leaks from the pipe and runs down the outside of the pipe to the stove, it may catch fire. More often, however, fires are caused by a build-up of creosote inside the pipe and chimney.

Installing the System

Fire prevention begins with using the right materials and installing them properly. In most cases, this involves following the rules outlined below. However, some heaters require different treatment. In these cases, follow the manufacturer’s instructions and, when in doubt, check with your local fire department.

The Heater

  • Check the heater for broken parts and cracks. Have any problems repaired before installation.
  • Locate the heater so that no more than 10 feet of stovepipe will be needed to reach the chimney.
  • Leave a space of at least three feet between the heater and any combustible materials, such as walls and furniture. If this much space is not available, install a protective shield of fire-resistant material around the stove. Leave a space of at least one inch between the protective shield and the walls.
  • Unless the floor is masonry, install an insulating pad under the stove. The pad can be made from 1/4-inch asbestos millboard covered with sheet metal. The pad should extend at least 12 inches beyond the sides and back of the heater. At the front or loading side, the pad should extend at least 18 inches to protect against hot coals that may be spilled during loading. As well, there should be a space of at least four inches between the insulating pad and the bottom of the heater.
  • Do not use brick or stone in place of insulating materials. If they are used around the heater for decoration, insulate them from the floors and walls.
The Smokepipe
  • The smokepipe should be no longer that 10 feet, and preferably less.
  • Use only pipe designed for use as a smokepipe. The pipe should be 24- or 22 gauge metal.
  • Use pipe that is the same size as the heater’s flue collar. Do not reduce the size of the pipe between the heater and the chimney.
  • A section of pipe is usually plain on one end and narrow and crimped on the other. Install the pipe so the narrow, crimped end is closest to the heater. This will prevent creosote from running down the outside of the pipe.
  • For bends in the pipe, use pre-shaped 45- and 90-degree elbows. There should be no more that two bends in the full length of the smokepipe.
  • If the heater does not have a separate damper for the smokepipe, install one in the pipe close to where the pipe joins the heater.
  • Join the sections of pipe together with at least three sheet metal screws at each joint.
  • Slope the pipe upward from the heater toward the chimney. The slope should be at least 1/4-inch for every foot of length.
  • Leave at least 18 inches of clearance between the ceiling and the pipe at all points.
  • If the pipe has to pass through a wall or a ceiling, insulate it with a thimble or firestop designed for this purpose.
  • Fasten the pipe securely where it enters the chimney. Do not extend the pipe into the chimney beyond the flue liner.
The Chimney
  • If an existing chimney is to be used, check it for cracks and obstructions. Correct all such problems before connecting the heater to the chimney.
  • Do not connect the heater to a chimney flue serving another fireplace, or an oil or gas heater or furnace.
  • If a new chimney is needed, purchase one designed for use with a wood heater. Other types will not be strong enough to withstand the heat produced buy a wood fire.
  • Make sure the chimney is large enough for the size of the heater being used.
  • When installing a new chimney, provide adequate clearance between the chimney and the roof, and at least two feet above any section of the roof within 10 horizontal feet.
Operating the System

Once the system is installed, it must be operated properly and receive regular maintenance to remain safe. Proper operation begins with using only paper o kindling to start fires. Never use highly flammable liquids, such as gasoline or kerosene. Also, never use the heater as an incinerator to burn large volumes of light material, such as paper excelsior or pine needles.

Keep flammable materials, such as paper and firewood, well away from the heater. Children should be taught to stay at a safe distance.

If recommended by the manufacturer, provide a layer of firebrick or sand in the bottom of the heater. If the heater is an open-front type that can expose flames to the room, use a screen to prevent the escape of sparks and hot cinders.


All parts of the system require regular maintenance. In the case of the heater, check it for broken parts and cracks before firing it up each Autumn. Periodically recheck and clean the heater during the course of the heating season. Any damage should be repaired as soon as it is found.

Clean ashes into a metal container with a tight-fitting lid. After any live coals have cooled, dispose of the ashes a safe distance from the house.

The smokepipe should also be inspected at the start of each season, and several times during the year. The main problem will be creosote build-up, which can be detected by tapping the pipe. A clean pipe will give a metallic ting, while one with creosote build-up will give a dull thud. If the pipe is dirty, disassemble it and clean with a long-handled wire brush. Do this outside to avoid getting soot on furniture or walls.

While cleaning, check the condition of the pipe. Replace any section that is significantly corroded or weakened.

Chimney Cleaning

The chimney should be checked at least once a year for creosote build-up. Inspections should be more frequent if the heater is operated at very low draft settings, or if softwood or unseasoned wood is burned. Poor draft performance or increased smoking by the heater usually indicates a creosote build-up.

To clean the chimney, first make sure the fire is completely out. Then seal off the bottom of the chimney or smokepipe to keep creosote from getting into the house. A masonry chimney can be cleaned with a wire chimney cleaning brush or a burlap bag filled with straw, wire netting or similar material. The clear should just fit inside the chimney flue. Pulling it up and down inside the chimney should clean away the creosote.

Follow the manufacturer’s instructions for cleaning prefabricated metal chimneys.

The information and recommendations contained in this publication are believed to be reliable and representative of contemporary expert opinion on the subject material. The Farm Safety Association Inc. does not guarantee absolute accuracy or sufficiency of subject material, nor can it accept responsibility for health and safety recommendations that may have been omitted due to particular and exceptional conditions and circumstances.

Disclaimer and Reproduction Information: Information in NASD does not represent NIOSH policy. Information included in NASD appears by permission of the author and/or copyright holder. More