10/08/2024
Most steam heating systems were designed in the early 20th century largely in response to the 1918 Influenza pandemic. The airborne illness brought to light the need for a safe, automatically operated, comprehensive heating system to warm every room of a residence while providing ventilation through partially opened windows. Back then, the contractors, engineers, and boiler and radiator manufacturers of the day needed a term to express what quantity and size of radiators could be connected to a boiler to produce an effective result. The term would be used to express both the size of radiator for each room and the output of each boiler size and model. The measurement came to be called a “square foot of Equivalent Direct Radiation”, or EDR, and that’s the term manufacturers use this very day to express the potential output of a modern steam boiler or radiator.
Installing steam in a home or building back then was considered to be a very technical job that rarely fell to anyone other than highly-qualified engineers and installers who were committed to safety and limiting installation costs by carefully calculating all pipe diameters, radiators, and boiler sizes.
Today it’s an installer’s job to match the EDR output of a replacement boiler to the system’s ability to process that steam safely, effectively, and efficiently. The sum of the EDR of all the radiators in the home or building tells us the EDR output of the boiler we need to install.
Mismatching the boiler and collection of radiators creates all manner of lingering problems: banging pipes, hissing air vents, high fuel bills, unnecessary fuel usage, unbalanced heating, frequent boiler failures, and more.
There are some exceptions to this process but they are few and far between. If a potential boiler installer is not doing an EDR calculation in your home or cannot show you the proper math upon request then your replacement boiler size was probably a guess and may not be the most efficient choice for your home.