Eric is a member of Lopez Labs.  Eric’s involvement in testing is documented, in part, at the link to Lopez labs where you can also find additional tests from others at Lopez Labs.  There are many considerations in testing a Masonry Heater.  Some of the tests examine the materials, design, build, firing cycle and exhaust products.

Recent safety testing of Masonry Heaters governed by ASTM E-1602-94

Testing helps to establish how a masonry heater performs including particulate emissions, combustion efficiency, and overall efficiency.

Particulate emissions:
Particulates, alternatively referred to as particulate matter (PM) or fine particles, are tiny particles of solid or liquid suspended in a gas. In the case of wood burning, PM refers to particulates in exhaust gases (smoke) that exit the chimney and enter the atmosphere. PM consists of ash, tar, and other organic compounds.  The EPA is recently begun regulating PM2.5 which means that the smaller particles are now a concern for emissions regulation.
Combustion efficiency:
This refers the ability of the heater or stove to burn fuel. In terms of masonry heaters, this describes how completely the heater is burning the cord wood fuel load. If a stove is thought to burn clean it will have a high combustion efficiency and low emissions. Combustion efficiency is described as a percentage. For example, a combustion efficiency of 95% would mean that stove is able to burn 95% of the available matter in a given load of fuel, with 5% going up the stack (chimney) as waste, either in the form of gases or particulates.
Overall efficiency:
In wood burning appliances, overall efficiency describes how well the stove transfers energy released from combustion of the wood fuel source into usable heat energy radiated from the heater. In North America, this standard (in terms of cord wood combustion) will always subtract 15% as a loss to compensate for the moisture content in the fuel. As such, by North American standards the highest overall efficiency is 85%. In Europe (where the moisture factor is not subtracted in their testing standards) the highest potential overall efficiency is 100%. This is good to keep in mind when comparing data from North American and European masonry heaters.Summary of Masonry Heater Technical PerformanceThe following summary information comes from the technical data produced from the testing of masonry heaters in North American testing labs. The formal testing of masonry heaters (in North America) began in the mid 1980’s and continues to the present.

Particulate Emissions:
The average of averages for the study data on masonry heaters is 2.9 g/kg PM, with the overall range typically found to be between 1.4 to 5.8 g/kg PM. Every custom built heater is unique to some degree, and used by a different user with individual habits and with varying fuels. Many older, uncertified wood burning stoves average in the range or 12 g/kg PM. Modern EPA Phase 2 stoves average 6 g/kg PM. (MHA/HPBA White Paper, 2008)

Combustion Efficiency:
Most masonry heaters have a combustion efficiency ranging between 95 to 98%.

Overall Efficiency:
A well designed heater will have an overall efficiency between 70 and 85%.

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