Energy Efficiency and Your Wood-Burning Appliance

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How is Efficiency Measured for Residential Wood Burning Appliances?

There are different types of efficiencies often calculated for wood burning appliances.

  • Combustion efficiency represents a calculated measurement (in percent) of how well the wood burning device is converting the wood into useable heat. It does not reflect how much of the useable heat produced is transferred to the home.
  • Overall efficiency is the percentage of heat that is transferred to the space to be heated when a load of fuel (e.g., firewood, pellets) is burned.  Actual efficiency will vary depending on factors such as wood moisture, appliance operation and installation (e.g., outside piping, chimney height).

Overall efficiency is a better measure than combustion efficiency of the amount of heat that is delivered to the home.  Often advertisements will list combustion rather than overall efficiency since it is the higher of the two calculated efficiencies for any given device.  For example, an advertisement on a website or brochure may say “85% efficient” and although not specified, it is the combustion efficiency. The overall efficiency may be 10 % to 20% lower.  If you encounter an unspecified efficiency, you can check to see if the overall efficiency number for the specific device is included on EPA’s certified wood stove database.  If not, you may want to contact the manufacturer or ask your retailer to provide you with documentation of overall efficiency.

Where Can I Find Information to Compare Overall Heating Efficiencies of Wood-Burning Appliances?

The EPA requires manufacturers of all wood heating appliances subject to the 2015 air emission rules (i.e., any wood stove manufactured after May 1, 2015) to test and report overall efficiency as part of the EPA-certification process.  EPA has a list of certified wood heaters, hydronic heaters and forced air furnaces that include the overall efficiency by manufacturer and model. However, not all models on the list include an efficiency number if they were tested before 2015. If the efficiency number is missing, you may want to contact the manufacturer and ask for the “overall measured efficiency as measured using the Canadian B415.1 test method.” Beginning on May 16, 2020, all models on EPA’s certified wood stove, hydronic heater and forced-air furnace lists will have an overall efficiency listed. 

Is My Wood-Burning Appliance EPA-Certified and Energy Efficient?

To identify an EPA-certified appliance, look on the back for a metal tag, refer to your owner's manual or check EPA's list of certified appliances.   Note that wood stoves without glass doors are generally older models.  Wood heaters manufactured before 1990 burn wood less efficiently, which wastes fuel, pollutes outdoor air and creates dust in your home.  Replacing an old wood heater or fireplace with a more energy efficient EPA-certified appliance can save fuel, money, and protect you and your family's health. To learn more, visit Choosing Wood Burning Appliances. 

What are the Benefits of an EPA-Certified Stove?

  • Up to 50% more energy efficient
  • Save money, time and resources
  • Use 1/3 less wood fuel for the same heat
  • Reduce creosote build-up and the risk of chimney fires
  • Lower wood smoke pollution both inside and outside, including carbon dioxide (CO2), methane (CH4) and black carbon (particle pollution)

Compare old vs. new appliances in the Dirty Little Secrets brochure. 

Are Fireplaces an Efficient Method to Heat a Home?

Generally, a wood-burning fireplace is a very inefficient way to heat your home. Fireplace drafts can pull the warm air up the chimney, causing other rooms to be cooler. If you use central heat while burning in a fireplace, your heater will work harder to maintain constant temperatures throughout the house. Also, fireplaces do not burn as cleanly as EPA-certified wood heaters, creating 20 times the amount of air pollution. 

For more efficient heating with less smoke, ask your local retailer about gas, pellet, or EPA-certified wood fireplace inserts. You can also add gas log lighter kits to your existing fireplace. These devices make it easier to light a wood fire and provide more efficient start up. EPA is also working with manufacturers to bring cleaner burning fireplaces to the market through the voluntary fireplace program.

Tree Species: Energy per Cord

Trees at the top of the list have the most energy per cord, while those at the end have the least.

Hardest (long burning)
Ironwood
Rock elm
Hickory
Oak
Sugar maple
Beech
Yellow birch
Ash
Red elm
Red maple
Tamarack
Douglas fir
White birch
Manitoba maple
Red alder
Hemlock
Poplar
Pine
Basswood
Spruce
Balsam

Although they are less dense, the species in the lower half of the list can be excellent firewood for spring and fall because they make heat control easier and don’t tend to overheat the house.

Source:  Government of Canada, Burn It Smart

How Does the Moisture Content of Wood Affect Efficiency?

Wet wood can create excessive smoke which is lost heat.  Make sure firewood is dry, or “seasoned.”  Moisture meters allow you to test the moisture level in wood, and can be bought at hardware stores or on the Internet.  Properly dried wood should have a reading of 20% or less.  To properly dry wood:

  • Split wood into pieces 6 inches in diameter or smaller for faster drying.
  • Stack off the ground, split side down.
  • Cover top of stack to protect the wood from rain and snow.
  • Store for at least 6 months for softwood, and at least 12 months for hardwood.

If you smell smoke inside or see smoke coming out of the chimney, you may be burning wood that is too wet or have a problem with your stove or fireplace. If the smoke persists after burning dry wood and opening the damper to get a full fire going, find a Chimney Safety Institute of America (CSIA) or National Fireplace Institute (NFI) professional in your area.

If you burn wood pellets, make sure they are certified by the Pellet Fuels Institute (PFI) and always keep your pellet heater clean and well maintained.

What are the Benefits of Weatherization?

Sealing and insulating cracks and crevices in your home can help reduce overall heating needs and heating bills. Caulk around windows, doors, and pipes to seal air gaps and add weather stripping to doors and windows. Check out EPA's ENERGY STAR home improvements for additional tips. 

 

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Last updated on August 28, 2024