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How are low temp boilers usually rated?

  1. Gross rated in BTU/hr

  2. Net rated in BTU/hr or EDR

  3. Rated by efficiency percentage

  4. Rated by size and weight

The correct answer is: Net rated in BTU/hr or EDR

Low temperature boilers are usually rated by net in BTU/hr or EDR (equivalent direct radiation) because this takes into account the amount of thermal radiation required to maintain a steady temperature in a given space. Gross ratings, by comparison, only take into account the amount of raw heat output by the boiler, without taking into account the system's configuration. Efficiency percentage, choice C, is a way to compare boilers based on the amount of heat delivered versus the amount of energy consumed, but it is not a common method for rating low temperature boilers. Size and weight, choice D, may be factors in the overall rating of a boiler, but they are not the most important criteria for determining its thermal output.