What is it: Interim international guidelines for stove performance, including efficiency, total emissions, indoor emissions, and safety.  The goal is to provide a common and easy-to-understand terminology for governments, donors, investors, and consumers to make decisions about technology options.

How was it developed:  International Workshop Agreements are a streamlined process in the International Organization for Standardization (ISO) that can be a first step towards formal ISO standards.  IWA 11:2012 Guidelines for evaluating cookstove performance was unanimously approved in February 2012 by over 90 participants from 22 countries.

What do the Tiers mean:  The IWA framework rates cookstoves on four (4) indicators (efficiency, indoor emissions, total emissions, safety), each along 5 Tiers (0: lowest performing to 4: highest performing).  For each indicator, the Tiers boundaries are defined by quantitative values determined by laboratory testing.  The protocol that has been mapped to tiers is the Water Boiling Test 4.2.3 and the Biomass Stove Safety Protocol 1.1, although the IWA framework was designed to accommodate other protocols.

The goals of the IWA are to

  • set aspirational goals
  • provide clarity to non-technical audiences
  • communicate progress
  • allow organizations and countries to select specific indicators and tiers based on local priorities
  • harmonize different protocols.

The emissions rates that define Tier 4 for Indoor Emissions (the highest performing tier) were determined based on the World Health Organization’s Guidelines for Indoor Air Quality for pollutant concentrations.  Other Tier boundaries for Indoor Emissions were defined to be progressively lower relative to Tier 4.  This linkage from WHO and ISO guidelines demonstrates how performance standards can be used as an implementation strategy for health or environment goals.

What the tiers do not mean:  

  • The Tiers were not designed to be combined.  There is no “Tier 3 stove.”  Instead, the indicators are kept separate to provide flexibility for governments and organizations to set different goals.  For example, a stove might be “Tier 2 for efficiency, Tier 3 for indoor emissions, Tier 2 for total emissions, and Tier 4 for safety.”
  • Tier 4 is not the only acceptable level of performance.  Governments and organizations have a combination of environment, health, and livelihood goals, as well as different goals for affordability and scale.  The Tiers provide a flexible framework to evaluate the likelihood of technologies to achieve these goals.  The multiple Tiers from 0 to 4 were also designed to support incremental improvement over time.
  • The Tiers are not meant to replace the underlying quantitative metrics.  The Alliance supports public reporting of Tiers together with the quantitative metrics.
  • The IWA is not finalISO Technical Committee 285 is incorporating lessons learned from the interim application of the IWA as well as progress in protocol development (e.g. durability, charcoal stoves, griddle stoves).  Working Group drafts will be completed by the end of 2015.  
  • Tier 0 is not equivalent to the performance of a traditional stove.  Some improved stoves can have Tier 0 performance.  It is possible under certain usage conditions to achieve performance better than Tier 1 with a traditional stove.  
  • The Tiers do not completely predict environment and health impacts.  The Tiers define best possible stove performance.  Specific environment and health impacts are also determined by how often the stove is used, how the stove is used (including the quality of fuel), displacement of the traditional stove, and other behavioral factors that will influence exposure.

Tiers associated with WBT 4.2.3 and BSSP 1.1

The overall Tier is the minimum Sub-tier value within an indicator category.  For example, the Indoor Emissions Tier is the minimum of the Sub-tiers forPM2.5 and CO emissions.

More details, download:  

Full IWA document
Full IWA document from ISO