MEMORANDUM

DATE: February 20, 2013

SUBJECT: European Wood Heating Technology Survey Explanation of Data for Solid Wood Stoves 

and Boilers

FROM: Alden West, EC/R Inc.

Glenn Meganck, EC/R Inc.

TO: Gil Wood, EPA/OAQPS

David Cole, EPA/OAQPS

The ExcelTM spreadsheet (included as an attachment in this e-mail) provides data for solid wood stoves 

and boilers from the European Wood-Heating Technology Survey1(EWHTS). Both the stoves and boilers 

tables are provided in the format presented in the EWHTS and as a “sortable” table. A PM emission rate 

in grams per hour (g/hr) was calculated by multiplying the nominal load (MBtu/hr – converted to 

MMBtu/hr) by the TSP emissions (lb/MMBTU – converted to g/MMBTU). 

The data in the European Wood-Heating Technology Survey are useful for development of the 

Residential Wood Heaters NSPS although not all of the data are directly comparable to some of the data 

previously compiled for the NSPS. Some differences should be kept in mind: (1) The EWHTS provides 

emissions data as “dust” or “total suspended particulate (TSP),” which is defined as particles with a 

diameter of 45 micrometers (μm) or less, while the NSPS data is provided as particulate matter (PM), 

defined as particles with a diameter less than either 10 μm (PM10) or 2.5 μm (PM2.5). Both measures need 

clarification; the EWTHS test method does not use a dilution tunnel and thus the EWHTS “dust” does not 

include the condensibles [products of incomplete combustion] that would be measured by EPA Method 

28. This difference is believed to be very small for the higher combustion efficiency heaters that have less 

products of incomplete combustion. Although neither the EWHTS test methods nor EPA Method 28 

distinguishes between TSP and PM10 and PM2.5, studies have shown that over 85% of residential wood 

smoke emissions are PM2.5 or less. (2) The EWHTS provides data for European solid wood boilers, which 

often are low-pressurized systems whereas many current U.S. hydronic heaters are not pressurized. 

(3) The EWHTS provides data on stoves that burn wood in Austria, Denmark, Germany, Norway and 

Sweden; some of the tree species in these countries are different than those in the United States and 

therefore may have somewhat different emission characteristics when burned. (4) The EWHTS 

characterizes wood heaters based on “nominal load” (MBtu/hr). Although nominal load is believed to be 

similar to the “maximum capacity” as defined by NSPS Burn Rate Category 4, both EPA Method 28 and 

EN303-05 currently allow the manufacturers to specify the rated output capacity goal for the tests. This 

may not be a significant difference since most manufacturers use the highest value the heater can achieve 

for the durations specified in the owner’s manual. 

 

1 European Wood-Heating Technology Survey: An Overview of Combustion Principles and the Energy and 

Emission Performance Characteristics of Commercially Available Systems in Austria, Germany, Denmark, Norway, 

and Sweden, New York State Energy Research and Development Authority (NYSERDA). Final Report April 2010.
It should also be noted that the EWHTS ranked the top performing wood stoves based on the efficiency of 

the stove and CO emissions (as an indicator of combustion quality), whereas the top performers in the 

NSPS data are currently ranked solely based on PM emissions (grams per hour). Therefore, if wood 

stoves in the EWHTS data have low PM emissions they may still be excluded from the EWHTS “top 

performers” if they are inefficient or generate high CO emissions from incomplete combustion. Also, it 

should be noted that forced-air furnaces are not included in the EWHTS because European manufacturers 

and consumers consider forced-air furnaces to be an inferior technology/system compared to the other 

systems that can perform better.

Also, note that the efficiencies in the EWHTS tables are for gross combustion values, i.e., using the high 

heating value of the wood burned rather than the net combustion values, i.e., using lower heating value of 

the wood as typically advertised in Europe. The NSPS is expected to require testing and reporting of the 

gross values.