Equivalent direct radiation. One square foot of EDR gives off 240 Btu per hour on steam and about 150 Btu per hour on hot water at standard conditions. Techs count the radiators, look up the EDR of each by height, columns and sections, total it, and then choose a steam boiler whose net rating matches the connected radiation. Sizing a steam boiler to heat loss instead leaves part of the system cold.
Counted 620 square feet of EDR in the building, so we need a boiler with at least 620 net, never mind the heat loss calc.
On steam, size to the radiation, not the house. It is the opposite of what most hot water techs are taught.
Also heard as
- equivalent direct radiation
- square feet of radiation
Related terms
Rad
Short for radiator, especially the cast iron column or tube radiators of steam and hot water systems.
Boiler horsepower
A boiler capacity unit equal to 33,475 Btu per hour, or evaporating 34.5 pounds of water per hour from and at 212 degrees F.
MBH
Thousands of Btu per hour: the everyday unit for rating heating boilers, burners and heating loads.
Dead men
Steam heating slang for the long-gone engineers and fitters who designed and piped the steam systems that remain in service.