Conformity - November 2008 - (Page 43) Part 1—Solid Fuel Wood-Fueled Furnaces Wood stoves have been used for years for primary and supplementary heating in residential buildings. Today there are standalone furnaces capable of heating spaces up to 11,000 sq. ft. There are three different types of furnaces. The central furnace is a self-contained product that delivers heated air through ducts or heated water to the residence. The heated air is circulated by a fan (i.e., forced hot air) or natural convection (gravity feed). The combination furnace uses a combination of solid-fuel such as wood with fuel-oil. These furnaces can burn both fuels separately or simultaneously. They can have a common combustion chamber or separate combustion chambers. The third type of furnace is the supplementary furnace. The supplementary furnace is designed to connect into a common hot air system by means of a plenum, use of a heat exchanger, or directly connected into a boiler. These three types of furnaces are covered by a common safety standard, UL 391. The Canadian standard is CAN/CSA B366.1-M91. Most stoves sold in North America meet both UL 391 and CSA B355.1-M91. UL 391 4th Ed., Solid-Fuel and Combination Fuel Central and Supplementary Furnaces, was last updated in October 2006. This standard applies to manually fueled and solid-fuel furnaces, which are intended to burn fuels such as wood, coal, and other biomass fuels. The 4th edition has the following three changes from the previous edition: • Requirements for electrical convince receptacles; • Corrections to bonding conductor tests; • Miscellaneous references to NFPA 211, ANSI MC96.1, UL 61058 and wire size terminology. Electrical Safety Testing for Wood-Fueled Furnaces Electrical safety testing called out in UL 391 includes Dielectric Withstand testing, Bonding Joint testing and Bonding Conductor testing. Manufacturing and production testing requires that Dielectric Withstand testing be performed on every furnace. Dielectric Withstand testing requires hipot testing at 60Hz for one minute between live parts (mains) and dead metal parts, and between live parts of high voltage and live parts of low voltage. The test voltage between live parts and dead 901 Sheldon Dr., RTP (Cary), NC 27513 USA november 2008 Conformity 3 http://www.productsafet.com http://www.productsafet.com
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