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2 Methodology

2.1 Overview

The project methodology involved a number of discrete processes, including:

  • random selection of wood burners to test

  • development of a protocol for verifying wood-burner compliance

  • communication with interested parties

  • design verification.

Each of these is discussed in more detail below.

2.2 Random selection of wood burners

Wood burners randomly selected for inclusion in the performance review were sourced from the lists of 'authorised' and 'tested' wood burners published on the Ministry website.

At the time the project began these lists contained 66 authorised and 44 tested wood burners, respectively. There were some wood burners on both lists that were clearly the same, and these duplicates were removed before the random sampling took place. Where there were any doubts as to whether a wood burner was duplicated it was initially assumed they were different.

The objective of the sampling process was to randomly select two lists, including a list of 40 wood burners for the design verification testing and a list of 10 wood burners for the full emissions testing process. Wood burners could potentially be selected to be on both lists.

Burners were selected randomly to provide fairness and transparency. Because all manufacturers were open to inspection via either the purchase of a burner for testing or the inspection of a model in retail showrooms, there was no 'targeting' of any specific product. This approach also avoids relying on the goodwill of manufacturers to provide a product for review.

The tested and authorised lists were merged to create an initial list for sampling, which included 90 wood burners. A random number was generated and associated with each wood burner on the list. This list of random numbers was then sorted and the wood burners associated with the lowest 40 random numbers were selected for the design verification phase.

An analysis was then carried out to compare the distribution of randomly selected burners by manufacturer with the numbers of wood burners they have on the tested and authorised lists. Overall, the distribution of burners across manufacturers selected for inclusion was similar to the distribution on the tested and authorised lists.

Once additional detail had been obtained on the wood burners selected, it became apparent that two of the wood burners were duplicated, namely the Kent Insert and the Milan Caldo. These duplicates were then replaced by selecting the wood burners associated with the next two lowest numbers on the list of random numbers. Lists of the wood burners selected are attached as Appendix 1.

2.3 Development of a protocol for verifying compliance

The protocol is the agreed process by which the design verification testing was carried out. This protocol was developed by John Yolland in association with the project partners and a working group supplied by the New Zealand Home Heating Association in April/May 2006. A copy is attached as Appendix 2.

The objectives of the protocol are to:

  • introduce the rationale for the compliance verification project

  • specify the basis for selecting wood burners for verification

  • specify the dimensions that will be measured and the allowable tolerances

  • provide examples of verification failure

  • provide classifications of failure of the design verification phase and recommended remedial or punitive actions.

Given the potentially sensitive nature of this work it was considered to be important to have the support of the industry. The design protocol was reviewed by a working group of the New Zealand Home Heating Association before being finalised.

2.4 Communication with interested parties

As mentioned above, it was important to carry out this project in consultation and co-operation with interested parties. While the prime concern for the main project partners was to determine whether wood burners offered for sale match the wood burners for which approvals had been granted and/or test reports issued, it is also important for retailers to know that they are selling wood burners that are legally able to be installed in the various regions around New Zealand.

The NZHHA assisted in the process of communicating information about this project to member retailers and manufacturers.

2.5 Design verification

John Yolland was the project engineer for the design verification phase. This included developing the protocol and designing the information capture forms, as well as physically inspecting and reporting on each wood burner on the list.

John was supplied with details of test reports, manufacturer’s drawings, installation instructions and relevant documentation for each wood burner. This provided the basis to confirm whether the wood burners in the retailers’ showrooms matched the models for which approval had been granted and/or a test report issued.

John visited retailers in Auckland and Christchurch to locate the various wood burners on the list. He inspected each wood burner and measured relevant components and recorded the details. A brief report was then prepared on each wood burner. Verification was carried out between May and July 2006.

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