Full Description Preface This is the Sixth edition of ANSI Z21.56 / CSA 4.7, Gas-fired pool heaters. It supersedes the previous editions published in 2014, 2013, 2004, 2001, and 1998. Scope 1.1 This Standard applies to newly produced pool heaters (see Clause 3, Definitions), hereinafter referred to as pool heaters or appliances, constructed entirely of new, unused parts and materials, for heating non- potable water stored at atmospheric pressure, such as water in swimming pools, spas, hot tubs and similar applications: a) for use with natural gas; b) for use with manufactured gas; c) for use with mixed gas; d) for use with liquefied petroleum gases; e) for use with LP gas-air mixtures; f) for installation in applications intended to temper the entire flow of the primary circulating pool loop water prior to re-entering the pool; and g) For installation in applications for pool heaters intended to temper a portion of the primary circulating loop water diverted through the pool heater by mechanical means, and then re-enter and mix with the primary circulating loop water prior to entering the pool. 1.2 This Standard also applies to pool heaters intended for installation at a distance less than 5 ft (1.52 m) from the inside surface of a pool or spa, hereinafter referred to as close proximity heaters (see Clause 3). 1.3 This Standard also applies to pool heaters for indoor installation with draft hoods which are factory equipped with automatic vent damper devices (see Clause 3, Definitions), hereinafter referred to as vent damper devices. 1.4 This Standard also applies to pool heaters of other than the direct vent type which are factory equipped with electrically operated or mechanically actuated automatic flue damper devices (see Clause 3, Definitions), hereinafter referred to as flue damper devices. 1.5 If a value for measurement as given in this Standard is followed by an equivalent value in other units, the first stated value is to be regarded as the specification. 1.6 All references to psi throughout this Standard are to be considered gage pressure unless otherwise specified. 1.7 Clause 7 contains provisions that are unique to the United States. 1.8 Clause 8 contains provisions that are unique to Canada. 1.9 Special construction provisions applicable to a water heater designed for use with an optional listed conversion kit are outlined under Annex D. 1.10 Clause 2, Reference publications, contains a list of standards specifically referenced in this Standard, and sources from which these reference standards may be obtained. 1.11 In this Standard, \"shall\" is used to express a requirement, i.e., a provision that the user shall satisfy in order to comply with the standard; \"should\" is used to express a recommendation or that which is advised but not required; and \"may\" is used to express an option or that which is permissible within the limits of the Standard. Notes accompanying clauses do not include requirements or alternative requirements; the purpose of a note accompanying a clause is to separate from the text explanatory or informative material. Notes to tables and figures are considered part of the table or figure and may be written as requirements. Annexes are designated normative (mandatory) or informative (non-mandatory) to define their application.