Friday, June 6, 2014

A Review of Heating Fuel Calculators: The best and the biased

 Updated on August 22, 2016 - Most people who heat with wood or pellets do so partly because it saves them money.  To demonstrate this, stove manufacturers and retailers often include heating fuel calculators on their websites so consumers can estimate their actual savings.  So far so good.  The problem is that unlike fossil fuel furnaces, wood and pellet stove efficiencies are reported in a variety of ways and most stove manufacturer calculators are biased.  If you are a consumer, this blog will help you find reliable calculators and reliable typical efficiencies of hearth products.

The Alliance for Green Heat reviewed scores of the most popular fuel calculators and found many of them to be hard to use and biased.  Not surprisingly, we found that most heat calculators on commercial sites were biased in favor of the fuel or the stove technology that they were connected with.  Of the dozens of calculators we reviewed, we recommend two that are good for calculating savings with wood and pellet heating appliances: the USDA Forest Service and (We used to also recommend the Energy Information Agency calculator, but they removed it because of too many controversies over efficiency values, especially from the air source heat pump sector.)

 1.,  is run by independent hearth professionals and uses efficiency values that are based on available data, extensive knowledge and experience. The efficiency values are on the conservative side, reflecting estimated real world efficiency over time.   Users enter their own price for cord wood or pellets and then can use the suggested efficiencies provided by   Unlike the USDA calculator, uses an estimated 60% efficiency for EPA certified non-cat stoves and for older, uncertified stoves they estimated between 25 and 50% efficiency, depending on if its air tight or not. They provide realistic estimate of 55 - 65% efficiency for uncertified pellet stoves and 65 - 80% for certified pellet stoves.

2. The newly updated USDA Forest Service calculator is notable for including estimated values for both commercial and residential wood and pellet systems.  Like, it also provides more options for wood and pellet heaters, such as for uncertified (exempt) pellet stoves, so we recommend it over the EIA calculator. It also uses the outdated EPA default efficiencies, so we recommend using the updated efficiencies below, or the more conservative ones in

We think it’s important for heating fuel calculators to be transparent and show what stove efficiencies and fuel prices they are using, something many industry calculators usually don’t do.   While consumers can easily put in their own fuel costs, it is usually impossible for a consumer to put in an accurate efficiency level of a particular stove.  Few major US manufacturer provide a reliable efficiency of their stoves to their consumers that are clearly American (HHV), not European (LHV) heating values. Consumers should not rely on the efficiency numbers posted by manufacturers. We encourage consumers to use the average efficiency values listed below.

Many fuel calculators that focus on wood and pellet stoves do not disclose the efficiency numbers they use in the calculation so the consumer cannot know what the values and assumptions are.  Harman,  Quadrafire and Travis calculators are a good example of this.  HPBA and most industry calculators do not include a separate efficiency value for catalytic stoves, which have consistently higher efficiencies if they are used properly.

Data on Efficiency

There are some datasets based on standardized wood stoves testing.  Studies from Houck & Tiegs, Robert Ferguson, and OMNI labs are among the best sources available as of now (they are listed below).  Those studies and data sets indicate that non-cat stoves average between 68 and 72% efficient, significantly above the 63% EPA default efficiency that was set in the late 1980s.  There is little data on catalytic stoves, but we think the EPA default of 72% may not be too far off the mark.  We suspect the average today may be in the 75% range, and the most efficient ones that are listed on the EPA list average around 80%.

Theold   EPA default of 78% efficiency for pellet stoves is by far the most misunderstood, because that 78% only applied to EPA certified pellet stoves, not their less efficient cousins, the exempt pellet stoves.  We now know that the default efficiency was too high for both certified and uncertified pellet stoves.  New, certified pellet stoves average about 72% efficiency. An OMNI study found the average to be 68% and EPA tests referred to in paper by Jim Houck estimate 56% for exempt pellet stoves.  There is extensive misleading information about pellet stove efficiency not only from industry, but also from some US government sites.

Efficiencies of Phase 2 EPA qualified boilers range from 39% to 78%, with an average of 65% according to the EPA list of boilers.  An Intertek report cited a 55% average efficiency for Phase 2 boilers and the State of Maine gave them a 65% average.  Efficiencies for European pellet boilers certified to the EN303-5 standard are likely to be in the 75 – 85% range, although some that are oversized or without any thermal storage could be lower.

Non-cat wood stoves tend to be bunched between 65 - 75% efficiency.  However, pellet stoves can range from 45 - 80% efficiency.  Higher efficiency ones are more likely to be the EPA certified or the European pellet stoves.  Unlike non-cat and pellet stoves, catalytic stoves are much more likely to have reliable, actual efficiency levels posted on the EPA certified stove list and that is an excellent resource to select one of the highest efficiency catalytic stoves on the market today.

Wood stove efficiencies discussed here are derived from tests in strictly controlled lab settings.  For consumers, to get similar, optimal efficiencies it is vital to use seasoned wood (about 20% moisture content).

Our Recommendations

Our recommendations for heating fuel calculator efficiencies reflect values of a new appliance when it is being used with seasoned wood. After a year or two, appliances can lose 5 - 15 points in efficiency if they are not properly maintained, particularly boilers, pellet stoves and cat stoves which need periodic cleaning to maintain the average efficiencies listed below:  

EPA certified non-cat stove         70%
EPA certified cat stove                75%
EPA certified pellet stove            70%
Exempt/uncertified wood stove   54%
Exempt pellet stove                     65%
EPA Phase 2 outdoor boiler        65%
Exempt outdoor boiler                 45%
EN 303-5 pellet boiler                 80%


Ferguson, Robert. An Evaluation of Overall Efficiency for EPA Certified Non-catalytic Wood Heaters. Rep. Ferguson, Andors & Company, prepared for the Hearth Patio and Barbecue Association (HPBA)., 21 July 2011.

Houck, James E., and Paul Tiegs. Residential Wood Combustion Technology Review. Tech. no. EPA-600/R-98-174a. OMNI Environmental Services, prepared for the EPA Office of Research and Development, Inc., Dec. 1998. Web. .

Houck, James E. "Pick a Number, Any Number." Hearth & Home. N.p., Mar. 2009. Web. .

Li, Victor S. Conventional Woodstove Emission Factor Study. Rep. no. Study. Environmental Protection Operations Division,, n.d. Web. .

The Engineer’s Guide to Efficiency Requirements for Wood Burning Appliances. Rep. no. BPEE201-11. Intertek, n.d. Web. .


  1. I'd agree on your efficiency estimates, with the proviso that these were usually measured under laboratory conditions, with 20% moisture fuel.

    In a recent real world study by NYSERDA, an exempt boiler came in at 22%, and a 2 stage European pellet boiler came in at 44% when it was operated at below minimum rated capacity, to match the heat demand of a typical house in Syracuse in January.

  2. Thanks Norbert. That is a really important point and we just added a sentence in the blog about it.

  3. Let's not be too particular about efficiency numbers when the highly variable energy content and water content of the fuel has a larger impact on fuel costs.

  4. The woodstock folks are another woodstove manufacturer that posts efficiency numbers along with BlazeKing.