Wood Burning Stoves

Wood-burning stoves are an efficient source of supplemental and/or zone heating. Their energy efficiency rating is 40-65 percent of available usable heat; by comparison, most furnaces operate at about 70 percent efficiency.

About 70 percent of a stove's usable heat comes from radiation; therefore, it is important that it be made of a metal with a high conductivity rating, be a color that aids heat radiation, and have enough surface from which the heat can radiate. It should be airtight to aid combustion and lined to retain heat for prolonged radiation.

Cast iron and steel have almost identical conductivity ratings and both are suitable for stoves; however, the Insurance Information Institute recommends cast iron. In either case, the thicker the metal, the longer the stove will last.

A flat black finish is best, radiating 90-98 percent of usable heat. Paints and enamels radiate 70-90 percent, while shiny metallic finishes offer efficiencies of less than 60 percent.

The three general types of wood stoves are: box (radiating), airtight (circulating) and pellet-fed.

BOX STOVE

A box stove draws air for combustion through the door, is not tightly sealed, has no damper control and releases a great amount of unburned gases up the chimney. It radiates warmth through the firebox to the surrounding air. A box stove should never be left unattended.

AIRTIGHT STOVE

An airtight stove will have a sealed firebox and tight fitting door. It will have a manually operated or thermostatically controlled air-intake damper to allow air to circulate around the firebox and to control the rate of fuel consumption. It provides slow-burning heat for a long period with relatively little attention.

However, because the airtight stove is slow burning, it can cause heavy creosote buildup in the chimney and pipes. Chimney brushes or soot removers solve this problem.

PELLET-FED STOVE

This pellet-fed stoves are a newcomer on the wood stove scene. They use a processed wood pellet that resembles rabbit food and is fed to the stove's combustion chamber electronically. Pellet stoves have the advantage of having a steady and easily controlled fuel source. The only downside to them is that their electronic controls won't work if the power is out.

SAFETY FACTORS

Wood stoves present potential safety hazards including:

• Excess heat radiating from the stove, stovepipe or chimney.
• Sparks or hot coals flying outside the stove.
• Flames shooting out of chimney cracks.
• Heat conducted from the chimney to a combustible material.
• Flames or hot ashes spurting out of the chimney.

Most of these dangers can be avoided with proper installation. Stove manufacturers include detailed safety instructions with each product.

In addition, Underwriters Laboratory (UL) tests and lists stoves that meet standards developed in cooperation with the Fireplace Institute, the Wood Energy Institute and the National Fire Protection Association.

Other safety suggestions are:

• Read the instructions provided by the manufacturer for proper installation and follow them exactly.
• Allow a clearance of at least 36" on all sides of the stove to prevent scorching or possible fire. This distance can be reduced by installing approved radiation shields. Such shields should be placed under the stove on all surfaces except concrete.
• Keep as much of the pipe as possible inside the house to retain heat. The pipe should be well insulated where it passes through a wall or roof. The Wood Heating Alliance recommends using stove pipe-not galvanized steel ducts-to vent the stove to a chimney.
• To vent the stove into an existing chimney, the chimney should be clean, in good repair, of heavy material and large enough to handle the pipe. Furnace chimneys may not be heavy enough, but fire place chimneys usually are. If a fireplace chimney is used, however, the fire place must be sealed off below the stovepipe.
• The chimney should extend about 3' above the highest point of the roof and should always be kept clean and in good repair (as should the stove pipe).
• A stove designed to burn wood should be used for just that. Do not try to burn coal unless you have a special grate for coal. Some kinds of coal produce far more intense heat than wood and can damage a standard grate and perhaps even the inside of the firebox.

back to top

Check your state and local codes before starting any project. Follow all safety precautions. Information in this document has been furnished by the North American Retail Hardware Association (NRHA) and associated contributors. Every effort has been made to ensure accuracy and safety. Neither NRHA, any contributor nor the retailer can be held responsible for damages or injuries resulting from the use of the information in this document.