Finding the answer to this question is not a simple matter. Definitions are found in State Law, in the Code of Construction, and in manufacturers' literature. Rarely do these definitions agree.
Even within the industry, people are often confused by terminology dealing with water heating devices. What is important for our purposes, is that contractors, equipment owners and the enforcement
authority for the State agree on a common definition. According to the Oregon Boiler Law: Oregon Revised Statute (ORS) 480.525 defines water
heaters which are exempt from the Oregon Boiler Law as: "Domestic water heaters, designed for heating potable water, equipped with an approved pressure relieving device, containing only water and
that do not exceed:
(A) Capacity of 120 gallons;
(B) Water temperature of 210 degrees Fahrenheit;
(C) Pressure of 150 pounds per square inch gauge pressure; or
(D) Heat input of 200,000 BTU per hour
This definition agrees with that found in the Oregon amended Uniform Plumbing Code. Confusion begins when pressure equipment seems to fall within the parameters of the water heater exemption,
but is not intended for the same purpose. Pressure equipment which exceeds these parameters, or is not intended by design for the heating of potable water, must be constructed in accordance with
the ASME Boiler and Pressure Vessel Code, Section IV (heating boilers), and consequently is classified as a "boiler".
Two types of boilers frequently mistaken for "water heaters" include hydronic boilers and copper fin-tube pool and spa heaters. The manufacturers of pool and spa heaters frequently advertise
their products as "water heaters", even though the units are built and stamped in accordance with the ASME Code Section for Heating Boilers.
To add to the confusion, ASME Section IV Part HLW deals with construction of, you guessed it, potable water heaters! The scope of part HLW is for construction of water heaters
which have BTU input exceeding the scope of the Uniform Plumbing Code, but which are not constructed as hot water boilers.
From what has been explained, we can see that the Oregon Boiler Law does regulate water heaters. But they are water heaters built to the ASME Code, and intended for industrial use,
where large volumes of potable water are required.