The proper spelling of the term "acid boiler" is "ˈæsɪd ˈbɔɪlər," according to the International Phonetic Alphabet (IPA). This word is typically used to describe equipment used for the production of acidic liquids or gases, and the spelling is based on the English language's traditional spelling and pronunciation rules. Using the IPA can help ensure accurate pronunciation and understanding, especially for non-native English speakers.