The phrase describes a tool used to determine the necessary flow rate for a point-of-use or whole-house water heating system that lacks a storage tank. Gallons per minute (GPM) is the unit of measurement for the volume of water that flows through the heater within a minute. This calculation is vital for ensuring the selected heater can meet the hot water demands of a household or business. For example, a shower might require 2.5 GPM, while a washing machine needs 2.0 GPM. Understanding these individual requirements allows for the selection of a water heater that can simultaneously support multiple hot water applications.
Accurate assessment of needed water flow is paramount in preventing unsatisfactory experiences like cold water bursts during showers or delays in filling bathtubs. Using a tool to compute the required GPM helps ensure the appropriate size of the tankless water heater is chosen. Historically, reliance on guesswork or averages led to under- or over-sized units, resulting in either insufficient hot water or unnecessary expense. The ability to accurately estimate the needed flow capacity offers a pathway to energy efficiency, lower utility bills, and user satisfaction.
