Equivalence of direct radiation
Measured in square feet, the reference standard for EDR is the mattress radiator invented by Stephen J. Gold in the mid 19th century.
EDR was originally a measure of the actual surface area of radiators. As radiator (and later convector) design became more complicated and compact, the relationship of actual surface area to EDR became arbitrary. Laboratory methods based on the condensation of steam allowed for very accurate measurements.
- http://www.heatinghelp.com/newsletter.cfm?Id=157 mattress radiator
- Harding, Louis Allen; Willard, Arthur Cutts (1929). Mechanical Equipment of Buildings. Vol I. New York: John Wiley & Sons.
- Emerick, Robert Henderson (1951). Heating Design and Practice. New York: McGraw-Hill.