This chapter shall not apply to the following boilers, unfired pressure vessels and domestic hot water tanks:
(1) Boilers and unfired pressure vessels under federal regulation or operated by any railroad subject to the provisions of the interstate commerce act;
(2) Unfired pressure vessels meeting the requirements of the interstate commerce commission for shipment of liquids or gases under pressure;
(3) Air tanks located on vehicles operating under the rules of other state authorities and used for carrying passengers, or freight;
(4) Air tanks installed on the right-of-way of railroads and used directly in the operation of trains;
(5) Unfired pressure vessels having a volume of five cubic feet or less when not located in places of public assembly;
(6) Unfired pressure vessels designed for a pressure not exceeding fifteen pounds per square inch gauge;
(7) Tanks used in connection with heating water for domestic and/or residential purposes;
(8) Boilers and unfired pressure vessels in cities having ordinances which are enforced and which have requirements equal to or higher than those provided for under this chapter, covering the installation, operation, maintenance and inspection of boilers and unfired pressure vessels;
(9) Tanks containing water with no air cushion and no direct source of energy that operate at ambient temperature;
(10) Electric boilers:
(a) Having a tank volume of not more than one and one-half cubic feet;
(b) Having a maximum allowable working pressure of one hundred pounds per square inch or less, with a pressure relief system to prevent excess pressure; and
(c) If constructed after June 10, 1994, constructed to American society of mechanical engineers code, or approved or otherwise certified by a nationally recognized or recognized foreign testing laboratory or construction code, including but not limited to Underwriters Laboratories, Edison Testing Laboratory, or Instituto Superiore Per La Prevenzione E La Sicurezza Del Lavoro;
(11) Electrical switchgear and control apparatus that have no external source of energy to maintain pressure and are located in restricted access areas under the control of an electric utility;
(12) Regardless of location, unfired pressure vessels less than one and one-half cubic feet (11.25 gallons) in volume or less than six inches in diameter with no limitation on the length of the vessel or pressure;
(13) Domestic hot water heaters less than one and one-half cubic feet (11.25 gallons) in volume with a safety valve setting of one hundred fifty pounds per square inch gauge or less;
(14)(a)(i) Miniature hobby boilers that have been certified by an inspector as of June 7, 2018; or
(ii) Miniature hobby boilers that have not been certified by an inspector as of June 7, 2018, but that receive certification from the chief inspector prior to being placed in service.
(b) For the purposes of this subsection, “miniature hobby boilers” means those that do not comply with the code requirements of the American society of mechanical engineers adopted under this chapter and do not exceed any of the following limits:
(i) Sixteen inches inside diameter of the shell;
(ii) Twenty square feet of total heating surface;
(iii) Five cubic feet of gross volume of vessel;
(iv) One hundred fifty p.s.i.g. maximum allowable working pressure; and
(v) The boiler is to be operated exclusively not for commercial or industrial use.


FindingIntent1994 c 64: See note following RCW 70.79.095.